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Symposium V: Functional Materials for Chemical and Biochemical Sensors

April 10 - 13, 2007

Chairs

Elisabetta Comini SENSOR, CNR-INFM Brescia University Via Valotti 9 Brescia, 25133 Italy 39-030-3715706		Pelagia-Irene (Perena) Gouma Dept. of Materials Science and Engineering State University of New York-Stony Brook (SUNY) 314 Old Engineering Bldg. Stony Brook, NY 11794-2275 631-632-4537
Vincenzo Guidi Dept. of Physics University of Ferrara Via Saragat 1 Ferrara, 41100 Italy 39-0532-974284		Xiao-Dong (XD) Zhang Center for Materials Science Bose Corporation M/S 415 The Mountain Framingham, MA 01701-9168 508-766-1367

Symposium V presentations will appear in the "Proceedings Library"
of the MRS Website
(www.mrs.org/publications_library)

---

* Invited paper

SESSION V1: Inorganic Materials for Sensing I
Chairs: Elisabetta Comini and Vincenzo Guidi
Tuesday Morning, April 10, 2007
Room 2008 (Moscone West)
8:30 AM *V1.1
Oxide Nanobelt Based Nanosensors. Zhong L. Wang, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia.

Semiconductor nanowires, nanobelts and related nanostructures are unique for sensor applications because of their single-crystalline structure, large surface-to-volume ratio and high stability. Nanowires and nanobelts exhibit optimal structural characteristics for both high sensitivity and long-term stability. They may also possess high selectivity by integrating nanowires of different surface characteristics into an array. In this work, three-dimensional (3D) tungsten oxide nanowire networks have been demonstrated as a high-surface area material for building ultrasensitive and highly-selective gas sensors. Utilizing the 3D hierarchical structure of the networks, high sensitivity has been obtained towards NO2, revealing the capability of the material to detect concentration as low as 50 ppb. Utilizing the coupled piezoelectric and semiconducting dual properties of ZnO, we demonstrate a piezoelectric-field effect transistor (P-FET) that is composed of a ZnO nanowire (NW) (or nanobelt) bridging across two ohmic contacts, in which the source to drain current is controlled by the bending of the NW. This P-FET has been applied as a force/pressure sensor for measuring forces in nano-Newton range and even smaller with the use of smaller NWs. An almost linear relationship between the bending force and the conductance was found at small bending region, demonstrating the principle of nanowire based nano-force- and nano-pressure-sensors.


9:00 AM V1.2
FT-IR and Electrical Characterization of Tin-Oxide Nanowires. Davide Calestani¹, Sara Morandi², Giovanna Ghiotti², Roberto Mosca¹, Andrea Zappettini¹ and Mingzheng Zha¹; ¹IMEM-CNR Institute, Parma, Italy; ²Dip. Chimica I.F.M. and NIS Centre of Excellence, Università di Torino, Torino, Italy.

Chemical sensors based on Metal Oxide nanowires (NWs) have shown excellent properties. Due to the high surface to volume ratio, high sensitivity was demonstrated [1]. In particular, tin-oxide nanowires show a strong luminescence band, whose intensity depends on the presence of particular gas species, so that an optical sensor was proposed [2]. For the application of SnO₂ NWs as chemo-resistive gas sensors the characterization of their electronic and electrical properties is crucial. In this presentation we report about a thorough characterization of tin-oxide nanowires performed by Fourier Transform Infrared Spectroscopy (FT-IR) and electrical techniques. SnO₂ nanowires (with diameters in the 30-100nm range) have been grown on alumina substrates by the physical vapor transport technique at a temperature of about 900°C [3]. For the IR analysis, after a pre-treatment at 500°C in vacuum and in dry oxygen, samples underwent treatments in ethanol, CO or NO₂ at temperatures up to 500°C. After each treatment the sample was cooled down to room temperature and an absorption FT-IR spectrum was recorded. The IR spectra of the SnO₂ NWs show, together with the vibrational absorptions of the test-gas and its decomposition/red-ox products, a very broad electronic absorption with a rather sharp edge at approximately 1600cm^-1 (0.20eV) and a maximum at about 2380cm^-1 (0.29eV). In agreement with previous findings [4], we ascribe this absorption to the photo-ionization of mono-ionized oxygen vacancies (V_O+ + hν → V_O2+ + e^- (C.B.)). The intensity of this spectroscopic feature is found to increase with the temperature of the reducing treatment. For the same temperature and gas pressure the electronic absorption is more intense in the presence of ethanol with respect to CO. On the contrary, the effects of an oxidizing gas, such as NO₂, are not detectable. It is worth noting that in bulk SnO₂ the electronic levels related to mono-ionized oxygen vacancies were determined to lie 0.15eV below the conduction band [5]. In order to verify the respective positions of the electronic absorptions, spectra recorded on SnO₂ NWs are compared to those of a SnO₂ powder prepared in laboratory by a sol-gel method. The shape of the powder absorption is different from that of nanowires, since the edge is broader and the maximum is located at about 1700cm^-1 (0.21eV). Thus the energy level associated to the mono-ionized oxygen vacancy seems to be deeper in the nanowires than in the powder material. Results obtained by FT-IR absorption spectroscopy are compared to those achieved by thermally stimulated current and impedance spectroscopy measurements and discussed with reference to the literature. [1] E.Comini et al., Sens. Actuators B, 111-112(2005), 2 [2] G.Faglia et al., Appl. Phys. Lett., 86(2005), 011923 [3] D.Calestani et al., J. Crystal Growth, 275(2005), e2083 [4] A.Chiorino et al., Sens. Actuators B, 44(1997), 474 [5] S.Samson, C.G.Fonstad, J. Appl. Phys., 44(1973), 4618


9:15 AM V1.3
Growth and Sensing Property of Aligned Cd1-xZnxS Nanowires Arrays Shih-Yuan Lu, Yi-Feng Lin and Yung-Jung Hsu; Dept. of Chemical Engineering, National Tsing-Hua University, Hsin-Chu, Taiwan.

Aligned plain CdS and ternary Cd1-xZnxS nanowires arrays were successfully fabricated via a non-catalytic and template-free MOCVD process, and their sensing ability toward tyrosine amino acid was demonstrated. These nanowires were grown on top of a 1μm thick buffer layer formed in-situ on the silicon substrate. The nanowires were with diameter of 20-30 nm and length of 500-700 nm. With increasing deposition temperature from 300 to 400 oC, the composition of the ternary nanowires became more ZnS-rich. A plausible growth mechanism for the nanowires was proposed and discussed. Basically, the morphology of the growing deposit turned from 2-D film to 1-D nanowire because of the drive for higher surface-to-volume ratio morphology caused by the reduction of precursor vapor supply toward the latter stage of the deposition. The X-ray diffraction (XRD) analysis and selected area electron diffraction pattern (SAED) not only confirmed the plain and solid solution nature, but also showed the hexagonal single crystalline structure of the nanowires. The dominant growth direction in the c-axis was also clearly revealed in the XRD patterns. The x values of the ternary nanowires were determined with the energy dispersive spectrum (EDS) data to be 0.21 and 0.44 for the ternary nanowires prepared at the deposition temperatures of 300 and 400oC, respectively. In addition, as evident from the HRTEM images, the nanowires grew along the [0001] direction of the hexagonal crystalline phase of CdS, consistent with the XRD analysis. The PL emission peaks of the nanowires were found located at 535, 498, and 473 nm for the x values of 0, 0.21, 0.44, respectively, all near band edge emissions and demonstrating the color tunability achieved with adjustment of the composition of the ternary nanowires. These nanowires were further demonstrated their sensing ability toward tyrosine amino acid by using photoluminescence intensity and electric resistance of the nanowires as the detecting measure. Tyrosine amino acid was dissolved in phosphate buffer solution (PBS) and the concentration of tyrosine was controlled by changing the amount of PBS. At the tyrosine concentration of 1mM and pH value of 7, the plain CdS nanowires showed better tyrosine sensing properties than that of the ternary nanowires. At the pH value of 7, the amino group (NH3+) of the adsorbed tyrosine scavenged electrons from the nanowire surface to reduce the PL intensity of the nanowires. This same effect also led to an increase in the electric resistance of the nanowires. The incorporation of ZnS, a wider energy band gap material, reduces the free charge carrier concentrations in the ternary nanowires and thus increases the electric resistance of the nanowires. The stronger bonding between Zn and S than that between Cd and S results in less electron scavenging effect produced by the absorbed tyrosine and thus less sensitivity in detection of tyrosine for ternary nanowires.


9:30 AM V1.4
Low-Temperature Solution Processing of Oxide Nanocrystals and Their Application in the Processing of Improved Chemical Sensors Mauro Epifani¹, Jordi Arbiol^2,3, Elisabetta Comini⁴, Raul Diaz², Eva Pellicer², Pietro Siciliano¹, Guido Faglia⁴ and Joan R. Morante²; ¹Istituto per la Microelettronica ed i Microsistemi, CNR-IMM, Lecce, Italy; ²Departament d'Electronica, University of Barcelona, Barcelona, Spain; ³Serveis Cientifico-Tecnics, University of Barcelona, Barcelona, Spain; ⁴SENSOR Laboratory, CNR-INFM, Brescia, Italy.

The processing of gas-sensing devices by using oxide nanostructures is expected to provide enhanced performances with respect to conventional materials, as concerns, for instance, the sensitivity and the response times of the device. Thus, an increasing effort is being devoted to the synthesis of metal oxide nanostructures by both physical and chemical approaches and the processing of gas-sensing devices. In this work, we present a novel and powerful solution technique for the preparation of metal oxide nanocrystals, together with several examples of their application in the processing of highly sensitive devices. Metal oxide sols were injected into hot (160°C) solutions of an amine in tetradecene, followed by heating for 3 hours. This procedure allows the formation of self-limiting nanoreactors, whose size is determined by the equilibrium between the catalysis and the hindering of the sol-gel transition that simultaneously occur by the action of the amine. Purification of the product and further heat-treatment resulted in pure oxide single nanocrystals, with a size of few nanometers, that were characterized both from a structural and chemical point of view by a variety of techniques (X-ray diffraction, Transmission Electron Microscopy, Fourier Transform Infrared Spectroscopy, Thermal Analyses). The technique has a broad range of applicability, allowing the synthesis of, for instance, SnO₂, In₂O₃, TiO₂, ZnO, Ga₂O₃, Fe₂O₃, NiO, MnO₂, NiFe₂O₄, CuFe₂O₄, CoFe₂O₄ nanocrystals. In this work we have focused on the processing of gas-sensing devices by using SnO₂, In₂O₃ and Pd-SnO₂ nanocrystals. The performances of the resulting devices are outstanding in the sensing of various gases ranging from NO₂ to ozone, acetone, ethanol and carbon monoxide. In particular, responses of several orders of magnitude were obtained from the SnO₂ based devices even at room temperature to NO₂, and at moderate temperatures to O₃. On the other hand, In₂O₃ based devices provided a response of almost seven orders of magnitude to ozone at 350°C, but even at room temperature they can easily reveal 60 ppb of ozone, while they provide high responses to NO₂ at about 200°C. Moreover, both systems provide high respons even to reducing gases (acetone, ethanol) at working temperatures of about 300°C. The results confirm that the reduced size of oxide grains (4-6 nm) can be expected to give rise to high responses, but the results are also an indication about the importance of keeping a porous structure of the sensing layer. We will discuss about the mild processing, without high-temperature treatments, which was employed for preparing the final devices by drop-coating techniques. The whole process is very promising towards the achievement of sensors with improved performances but requires technological improvements in the device-processing step. Many aspects of fundamental interest are disclosed, related to the electrical properties and the surface chemistry of the oxide nanocrystals.


9:45 AM V1.5
Visible-Range Luminescence Study in Indium Oxide Nanowires Davide Calestani¹, Mingzheng Zha¹, Margherita Mazzera¹, Laura Lazzarini¹, Andrea Zappettini¹, Giancarlo Salviati¹, Carlo Paorici² and Lucio Zanotti¹; ¹IMEM-CNR Institute, Parma, Italy; ²Dip. Fisica, Università di Parma, Parma, Italy.

Recently the great potential of metal oxides nanowires (NWs) for gas sensor applications has been studied. SnO₂, ZnO, In₂O₃ were grown in the nanowires form by several research groups and their sensing properties have been tested (e.g. see [1-2]). To understand the sensing mechanism of nanowires-based sensors, the electronic properties and the defects in metal oxide nanowires is currently under investigation. Recently we reported some results concerning the role of oxygen vacancies in SnO₂ NWs [3]. In the present study we tried to get some information about the electronic properties of In₂O₃ nanowires, mainly by mean of an in-depth luminescence characterization of samples prepared in our laboratory. In₂O₃ nanowires were grown by a vapor transport process, starting from In. The nanocrystals were grown directly on alumina and silicon substrates. Morphological and structural properties have been studied by Scanning and Transmission Electron Microscopy (SEM and TEM) imaging and X-Ray Diffraction techniques. Depending on the growth conditions, the obtained nanocrystals have different thickness, ranging from “wide” 1-2μm nanobelts (rectangular section) to very thin 10-20nm nanowires (round section). They are generally single-crystals and can grow up to several hundreds of μm in length. Though bulk In₂O₃ cannot emit light at room temperature (RT), we observed that these nanocrystals are characterized by luminescence emission in the visible range. Both Photoluminescence (PL) and Cathodoluminescence (CL) spectroscopy have been performed on the samples, focusing on large areas and on single nanowires respectively. A wide emission band with maximum at about 580nm has been revealed at RT. Studying its line shape it is possible to observe that the band is the convolution of two or more broad peaks. When the temperature is decreased down to 12K, the integrated emission intensity increases and the band maximum shifts to 615nm, probably as a consequence of the different weights of the component peaks. The origin of this band is not yet clear but we are inclined to exclude the role of impurities because the starting material is 6N-pure, it should be further “purified” by the vapour transport process and the emission is independent on the substrate material. At low temperature another emission band appeared at about 430nm, whose integrated intensity also increases by decreasing the temperature. In agreement with literature data we associated this emission to the presence of oxygen vacancies. This hypothesis has been confirmed by an annealing treatment of the samples in an oxygen-rich atmosphere at 1000°C. This “forced oxidation” resulted in a complete suppression of the emission at 430nm. The results are discussed in order to evaluate their influence on the In₂O₃ NWs properties. [1] Z.W.Pan, Z.R.Dai, Z.L.Wang, Science, 291 (2001), 1947 [2] E.Comini et al., Appl. Phys. Lett., 81 (2002), 1869 [3] R.Mosca et al., Mater. Res. Soc. Symp. Proc., 915 (2006), 0915-R04-06


10:30 AM *V1.6
Gas Sensors Based on Metal Oxides: What One Can Learn About the Surface Reactions from in-situ Electrical and Spectroscopic Techniques. Udo P. Weimar, Physical Chemistry, University of Tuebingen, Tuebingen, Germany.

On the surface of a metal oxide one can find sites (defects, additives, etc.) that can play a role in different processes, namely: gas reaction, charge transfer with the bulk and both. They can be useful for the catalytic or sensor function or just kind of interference. The understanding of their role is, in all cases, useful for both catalysts and sensors. The characterisation of charge transfer between the catalyst and adsorbed species at the surface of the catalyst in working conditions provides important information about the mechanism of the catalytic reaction, it allows to distinguish between: (i) delocalised and localised chemisorption, (ii) donor and acceptor type of the interaction as well as to study electron transfer effects and electron affinity changes and dipole contributions. We use a portfolio of specially adapted in-situ (“operando”) electrical and spectroscopic techniques to characterise the sensors in normal working conditions (total pressure: 1 bar, total flow: 10-1000 ml; relative humidity: 0-90%, operating temperature of sensors: 300-700 K; dosing system for gases: few ppb - 100%): - DC resistance measurements give information about electronic n- or p-conductivity as well as about delocalised phenomena which accompanies the electron transfer between the solid and adsorbed species. - AC impedance spectroscopy provides knowledge on the different contributions (surface, bulk) to catalytic reactions and gives an additional information about adsorbed surface species (due to the dependence of the capacitance C on the dielectric constant, which is influenced by adsorption of molecules with different dipoles. - Work function change measurements provide insight about surface reactions (oxygen species, donor-acceptor interaction); it is happens because the work function changes in-duced by gas exposure follow the change in band bending and electron affinity. - Simultaneous conductance and work function change measurements additionally provide insight about surface reactions where free charge carriers are not involved and surface species that are not carrying a net charge, such as dipoles. The different contributions to the work function change can be determined according to the well known relationsships between them. - On line gas analysis (paramagnetic oxygen analyser, IR gas monitors (CO, CO2 etc.), chemiluminescence NOX analyser, IR ozone analyser, on-line MS) and catalytic conver-sion measurements give additional information about the reaction paths. - Infrared spectroscopy and especially DRIFT measurements are allowing for the identifi-cation of surface species involved in the processes in normal operation conditions. The description of the theory, experimental techniques and results of the case studies (CO and propane sensing (accompanied with catalytic oxidation) on Pd-doped SnO2) will be given in the presentation.


11:00 AM V1.7
Aligned ZnO Nanorod Arrays for Sensor Applications. David Andrew Scrymgeour, Clark Highstrete, Yun-Ju Lee, Stephen Howell, Erik Spoerke, Mark Lee and Julia W.P. Hsu; Sandia National Laboratories, Albuquerque, New Mexico.

Semiconducting zinc oxide is a key material for sensors because it can be grown as nanostructures via solution and vapor phase methods and it possesses important and useful optoelectronic and piezoelectric properties. These properties when coupled with the high surface to volume ratio make nanostructured ZnO an ideal candidate for sensor applications. Here, the impedance response to gaseous species from DC to 50 GHz is examined in dielectrophoretically-aligned ZnO nanorods. Surface modifications have been explored to change ZnO conductivity and provide specificity for dectection.<br /><br /> Piezoelectric zinc oxide nanocrystals are grown by solution techniques in dense vertically oriented arrays on silicon wafers. These ZnO hexagonal nanorods have diameters of ~250 nm and heights of ~3 μm with their [0001] polar axis growing from the substrate. These rods are placed into DI water suspensions by sonication and are then deposited onto the gaps in interdigitated and coplanar electrodes using AC dielectrophoresis. The density of the rods on the electrodes (number per unit distance) has been studied as a function of solution concentration, time, AC frequency, and both AC and DC biasing voltage. <br /><br /> The DC resistive response of ordered arrays of nanorods assembled on interdigitated electrodes when exposed to different gases (H₂, N₂, O₂, and ethanol vapor) have been measured in a gas chromatography system. These responses are compared to the responses of disordered mats of unaligned ZnO nanorods. The high frequency response of ZnO rods are examined by assembling the rods across the gaps between the center conductor and the ground planes of a microwave co-planar waveguide (CPW) so that the rods are aligned with the electric field of the propagating mode of the CPW. The transmission and reflection scattering parameters of arrays of ZnO nanorods have been measured from 0.01 to 50 GHz at room temperature using a network analyzer. Elimination of spurious signals was achieved by measuring two identical independent sets of CPWs, depositing the nanorods on one set while maintaining the other as a control, and measuring both sets again. This redundancy in measurement enables us to monitor and minimize the systematic measurement uncertainty and permits the determination of changes in the scattering parameters due only to the presence of nanorods. From the scattering parameters, the microwave power dissipation can be determined as a function of frequency for the arrays of nanorods. The magnitude and frequency dependence of the fractional power dissipation due to the nanorods will be discussed, especially with respect to high frequency sensor applications. <br /><br /> Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.


11:15 AM V1.8
The Development of Surface Plasmon Resonance Spectroscopy on Conducting Metal Oxides. Crissy Rhodes¹, Alina Efremenko¹, Mark Losego², Jon-Paul Maria² and Stefan Franzen¹; ¹Dept. of Chemistry, North Carolina State University, Raleigh, North Carolina; ²Dept. of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina.

Surface plasmon resonance (SPR) spectroscopy is a surface-sensitive optical technique used to characterize adsorbed biomolecules and to monitor biological binding events. This technique is based upon the detection of a shift in the surface plasmon resonance that occurs after the binding event. Plasmon resonance is a general phenomenon observed in all conductors and is a function of the charge carrier density (n) of the material as approximated by the Drude free electron model. This resonance can be observed as a sharp decrease in the intensity of the reflected light at a specific resonant angle. Typically, gold or silver with relatively large n (10^23 electrons/cm^3) have been used as substrates for SPR with detection in the visible spectral region. Consequently, conducting metal oxides (CMO)s with an intermediate charge carrier density of 10^20-10^21 electrons/cm^3 possess a plasmon band in the mid- to near- infrared region. Therefore, in our study, for detection of the SPR effect in the near-IR region a particular CMO of commercial interest has been chosen: indium tin oxide (ITO). This material is transparent in the visible range, and reflective in the IR range, which offers the possibility of multiplexing detection methods. Preliminary experiments have been performed using simple molecules such as hexadecanethiol, as an initial step toward the identification of the binding of biomolecules. In addition, the material properties of ITO have been varied to examine the dependence of the excitation of the SPR peak on these characteristics. ITO films are prepared by RF magnetron sputtering and the film resistivity is controlled by post annealing conditions in an oxygen atmosphere. One particularly insightful study involved the deposition of ITO films with different thicknesses. Within this thickness series, one can elucidate a direct dependence of the SPR effect on the skin depth. Skin depth is a measure of the penetration of an electromagnetic wave at the 1/e attenuation point and is a key factor for determining optimal thickness for various applications including biosensing and field evaluation of conductors. We have shown that in ITO thin films, the theoretical skin depth must be reached for the observance of an SPR effect and further increasing the thickness has additional effects. With the ease of the custom film deposition of ITO, this substrate seems ideal to study the dependence of the SPR effect on various material properties of the surface.


11:30 AM V1.9
Role of the Synthesis of Nanopowders in the Gas Sensing Behavior of Metal Oxides. Marco Nagliati, Maria Cristina Carotta, Vincenzo Guidi, Cesare Malagu and Giuliano Martinelli; Physics, University of Ferrara, Ferrara, Italy.

This work focuses on the synthesis of semiconducting metal oxides, the most widely used materials in thick films devices for gas sensing. The aim is to compare the sensing performances of metal-oxides powders obtained by means of sol-gel (SG) and hydrothermal (HY) method. The microstructure of powders is a fundamental parameter to evaluate if the material is suitable for gas sensing. Materials for chemical sensors have to be composed by nanometric and spherical shaped grains sintered in controlled conditions aimed to modulate surface barrier heights at inter-granular contacts. Semiconducting metal oxides are able to sense gases upon variations of their energy barrier. Consequently, the most widely accepted detection mechanism is related to the presence of surface states which induce a space-charge layer at the metal oxide surface. Reaction of the adsorbates with reducing gases results in an increase in the conductance in the case of n-type semiconductors. One of the main factors enhancing the detection properties of these oxides is their grain dimension. Sharp increase in sensitivity is in fact expected when the grain size becomes smaller than the space charge width. The same starting materials and hydroalcoholic solution were chosen for both SG and HY method. The work is focused on the different methodology and on the outcome related to the two methods (we describe step by step both of them). HY powders show smaller grains than SG powders maintaining spherical shape. A comparison among different handled HY powders shows the role of dwelling time (at fixed temperature) on the nanostructure of grains. The characterization of the materials will be based on XRD, BET, SEM and TEM analyses. Electrical properties will be investigated, too. Experimental observations on the HY material shows an increase in the response to reducing gases with the increase of grain size. In this work we will provide an explanation for this apparently anomalous behavior. It can be interpreted in the light of an utility factor which takes into account of the attenuation of gas concentration when going inside the porous sensing body.


11:45 AM V1.10
Nerve Agent Simulants Detection By Tin Oxide Nanowires. Andrea Ponzoni, Camilla Baratto, Sebastiano Bianchi, Elisabetta Comini, Guido Faglia, Matteo Ferroni and Giorgio Sberveglieri; Chemystry and Physics Dept., CNR-INFM SENSOR Lab. and Brescia University, BRESCIA, Italy.

In the last years, metal oxide nanowires appeared as one of the most interesting class of materials due to their peculiar morphological and structural features. Their reduced dimensions, which can be scaled down to the nm-level by properly addressing the synthesis parameters, together with their single crystal shape exhibiting well-defined crystallographic surfaces, allow to investigate properties of meso-scaled materials. Focusing on gas sensing, the reduced dimensions and the single crystal structure are promising properties to develop solid state gas sensors featuring high sensitivity together with improved stability. In this work we synthesized tin oxide nanowires by means of Vapor-Liquid-Solid (VLS) process in a tubular furnace preliminary evacuated at 0.01 mbar. We started from tin oxide powders heated at 1350°C, working at constant pressure of 100 mbar provided by an Ar flux. Nanowires grow on alumina substrates covered with Pt catalyst placed downstream at 300-500 °C. Morphology and crystalline degree of deposited materials have been characterized by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) highlighting they exhibit width ranging from 20 to 200 nm, length up to 200 mm and tetragonal phase. Conductometric gas sensors have been prepared depositing by sputtering Pt electrical contacts on nanowires structures and a Pt meander acting as heating element on the back side of the substrate. Gas sensing tests have been carried out by flow through method in a thermostatic chamber with controlled humidity. Dimethyl methylphosphonate (DMMP) has been chosen as target gas. Its importance in gas sensing field is strongly related to its molecular structure, similar to the Sarin nerve agent molecule. Because of this and its reduced toxicity, DMMP is usually adopted as Sarin simulant in the development of Sarin sensitive devices. Sarin Immediately Dangerous to Life or Health (IDLH) value is 30 ppb, so far DMMP has been tested in the concentration range between 20 and 90 ppb. The DMMP molecule, featuring different methoxy and methyl groups can interact in different ways with tin oxide surface, furthermore at high temperatures it can break resulting in more molecules each interacting separately with the sensitive layer. Poisoning effects are also foreseen because of the presence of P atoms in DMMP that, according to catalysis literature, can produce P2O5 molecules that bond to tin oxide surface and prevent further adsorption. Working temperature and humidity effects have been studied. Results have been compared with response obtained by tin oxide thin films synthesized by sputtering method. Short-term stability (few days) has also been studied and work is in progress to provide longer time stability data. Results highlight that both nanostructures exhibit similar performances in terms of best working temperature and response intensity, but improved stability has been observed with nanowire based devices.


SESSION V2: Inorganic Materials for Sensing II
Chairs: Guido Faglia and Vincenzo Guidi
Tuesday Afternoon, April 10, 2007
Room 2008 (Moscone West)
1:30 PM *V2.1
Multifunctional Chemical Sensors based on Wide Band Gap Materials. Anita Lloyd Spetz¹, Kristina Buchholt¹, Doina Lutic², Michael Strand², Per-Olov Kall³, Mehri Sanati² and Rositza Yakimova⁴; ¹Dep. of Physics, Chemistry and Biology, Applied Physics, Linköping University, Sweden; ²Chemistry, School of Technology and Design, Växjö University, Sweden; ³Dep Physics, Chemistry and Biology, Physical and Inorganic Chemistry, Linköping University, Sweden; ⁴Dep Physics, Chemsitry and Biology, Material Science, Linköping University, Sweden.

We have demonstrated SiC based FET chemical sensors, which respond to reducing gases like ammonia and hydrocarbons. These sensors are suitable for applications such as in flue gases and diesel exhaust. A new gate design makes it possible to measure both field effect and resistivity changes by the same device during gas exposure and in this way get more information about a gas mixture. Also, the use of nanoparticles as the sensing layers in FET chemical sensor devices has been explored. Au nanoparticles show an increased response to NO or NO2. Pd showed an interesting fractal particle formation and also increased sensitivity to NO, while Au impregnated In2O3 nanoparticles responded to hydrocarbons or NO depending on the Au content. Results from sensing with SiC/ ZnO devices modified with nanoparticles will be reported as well.


2:00 PM V2.2
Spectroscopic and Optical Characterization of nano-WO₃ as a Gas Sensing material. Krithika Kalyanasundaram¹, P. I Gouma¹, N. Ohashi² and H. Haneda²; ¹Department of Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, New York; ²National Institute of Materials Science (NIMS), Tsukuba, Japan.

There is no clear relation that associates the surface electronic properties of a metal oxide to the selectivity of that metal oxide towards a particular gas.The aim of this paper , therefore is to correlate the surface electronic structure of the metal oxide under study, namely WO₃, to its gas sensing behavior. Nanostructured WO₃ was prepared by using the sol-gel method and was annealed at two different temperatures (400°C and 515°C) to obtain specific polymorphs in the sensing films. Gas sensing experiments carried out revealed distinct differences in the response patterns between the two sensors. Thermal desorption spectroscopy (TDS), X-ray Photoelectron spectroscopy (XPS), Raman spectroscopy, photoluminescence (PL), and infra-red (IR) measurements were carried out on both of these polymorphs and the results will be discussed in relation to the gas sensing behavior of the metal oxide.


2:15 PM V2.3
Quasi-1D Organometallic and Metal Oxide Nanostructures as Gas Sensors: Fabrication, Functionalization and Prototype Devices Andrei Kolmakov, Physics, SIUC, Carbondale, Illinois.

Quasi 1-D chemiresistors made of metal oxides are close to occupy their specific niche in the real world solid state sensorics. Using single crystal individual nanowires and nanowire mats we have studied their performance in model as well as in real world environments. Along with generic high sensitivity, the major advantage of this kind of sensors with respect to available granular thin film sensors will be their size and stable, predictable and reproducible performance in a wide range of operating conditions. The performance of such a gas sensor and especially its sensitivity is determined by its materials-specific surface chemistry as well as the size and shape of its active element(s). The array of methods which allow one to fabricate, functionalize and characterize chemiresistors will be reported. In particular we have developed and tested experimental approaches to tune sensitivity and selectivity of these sensors as well as implemented new methods to monitor the surface processes on individual nanostructures. In particular, the influence of the bulk doping (with donors) and surface sensitization with catalyst particles Ni, Pd, along with radiation induced defects on the surface reactivity and selectivity were directly demonstrated. The above results were compared with gas sensing performance of the individual organometallic nanowires and 2D weblike films. The CuPc nanostructures exhibit excellent sensitivity and selectivity toward NOx in a wide temperature range. The advantages and challenges related with these organometallic chemiresistors will be discussed. Finally the prototypes of nanowire electronic noses and real world nanowire micromachined devices will be discussed and their characteristics will be demonstrated.


2:30 PM V2.4
Analysis of Time Constants Associated to the Chemical-Electrical Transduction Processes Using Bottom up Gas Nanosensors Based on Single Metal Oxide Nanowires. Juan R Morante, Francisco Hernandez-Ramirez, Albert Tarancón and Albert Romano-Rodríguez; Electronics, University of Barcelona, Barcelona, Spain.

The knowledge of the time constants associated to the interaction of gas molecules with the surface of nanocrystals becomes fundamental for the development of new functionalized materials and sensing devices. The main reason for the lack of data or for the shortage of complete models on the surface mechanisms taking place in the metal oxides is the high difficulty to have ideal or nearly ideal single-crystal surfaces in a reproducible way. On the other hand, it is very often that the vacuum experimental conditions do not fit with the application parameters and, as a consequence, the deduced behavior, reduced surface, remains far away from the actual working conditions. The sensing conditions require the presence of air (21% oxygen) which defines a surface properties with bridging oxygen’s and some bringing oxygen vacancies whereas, under vacuum conditions, we will have a reduced surface without bringing oxygen’s and with some “in-plane” oxygen vacancies. For avoiding these drawbacks, we have used nanowires as nanocrystal to study the kinetics associated to the chemical electrical transduction processes. Unlike to the small quasi spherical nanoparticles with not faceted surfaces, nanowires have well defined crystallographic directions as crystal surfaces as well as they are near a perfect monocrystal. No grain boundaries exist. Therefore, the electrical transduction effects induced by the adsorbed gas molecules onto the surface of these nanowires has straightforward been revealed from electrical measured performed on single individual nanocrystals. Nowadays, to study chemical-electrical transduction mechanism onto one individual nanocrystal is still a challenge. In this contribution, single SnO2 metal oxide nanowires have been used to define a bottom-up nanosensor based on single nanowire as individual nanocrystal for studying the temperature and concentration dependence of the kinetics transduction mechanisms. In the range that there is predominant the absorbed atomic oxygen, O-, from 190C to 340C, we have determined that the time constants, associated with the interaction with CO and humidity, show activation energy for both, response and recovery processes. The associated energies values, which present large variation range of several tens of meV, as well as the associated mechanisms will be presented and discussed as elements for improving gas sensor engineering based in metal oxide nanowires.


3:15 PM *V2.5
Photoluminescence in Nanostructured Materials and Applications to Gas Sensing. Pasquale Maddalena^1,2, Stefano Lettieri², Antonio Setaro², Camilla Baratto³ and Guido Faglia³; ¹Physical Sciences Dept., University of Naples, Napoli, Italy; ²CRS Coherentia, CNR-INFM, Napoli, Italy; ³SENSOR, CNR-INFM, Brescia, Italy.

In recent years much attention has been paid on nano-scale materials, because of their peculiar properties. Great efforts have been made in controlling the morphologies of these new structures, in order to tune their physical and optical properties. In particular, the search for nanostructured materials working as all-optical contactless gas sensors awakens great interest because of their potentialities for medical and environmental health purposes. Photoluminescence is an optical phenomenon which is strictly connected to the energy configuration of the material under investigation so that it is dependent on the radiative and nonradiative recombination mechanisms of the photogenerated charges. This is particularly interesting in the study of nanostructured materials since most of them exhibit a strong visible photoluminescence emission even at ambient temperature. Due to the high surface to volume ratio of these materials, charge carriers recombination phenomena are influenced by external conditions (temperature, humidity, surrounding gas) so that photoluminescence properties in controlled ambient can be exploited in view of possible applications in chemical sensing. Indeed, chemical sensing based on photoluminescence quenching in nanostructures, such as metal oxide nanocrystals/nanobelts, has been reported in recent years though the influence of structure defects on the emission process is not yet clear. To better understand the nature of the quenching process, both stationary and time resolved photoluminescence studies have been carried out in semiconducting metal oxide nanocrystals and nanostructured silica. Measurements performed in controlled conditions allow investigation of the role played by the oxygen vacancies as recombination traps in the emission process.


3:45 PM V2.6
Chemical and Biological Sensors Based Upon Polymer Electronics Timothy M. Swager, Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts.

This lecture will describe the conceptual design and optimization of chemical/biological sensors based upon conjugated polymers (CPs) and carbon nanotubes (CNTs). The ability of a CP or CNT to produce amplification in a fluorescence- or resistance-based chemosensor stems from the ability to transport optical excitations or electrical charge, respectively, over large distances. These transport properties provide increased sensitivity over small-molecule chemosensors. By adding new functional diversity, chemoresistive properties have been realized. In fluorescence sensors, the migration of an optical excitation increases the probability of an encounter with an occupied binding site. To impart specificity a variety of molecular recognition schemes, assemblies, and reactions have been employed. Recent applications in biosensory schemes will be discussed.


4:00 PM V2.7
Integrative Chemistry Portfolio toward Designing Vanadium Oxide Microscopic Fibers and Tuning their Sensors and Mechanical Properties Celine M. Leroy¹, Helene Serier¹, Marie-France Achard¹, Nathalie Steunou², Jacques Livage² and Renal Backov¹; ¹CNRS-Universite Bordeaux-I, Pessac, France; ²CNRS-Université Pierre et Marie Curie, Paris, France.

The rational design of complex hierarchical architectures with a preformatted idea about the properties to be reached is a new transversal concept labeled “Integrative Chemistry” that encompasses both the areas of soft matter, soft chemistry and biology.[1] In this issue sol-gel process can be associated to metastable thermodynamic systems (air-liquid or biliquid foams) to design new macrocelluar materials.[2-4] We can substitute this macroscopic pattern by an external field, as it is the case for instance when applying a shear rate over a syringe out coming droplet during an extrusion process. Among inorganic polymers, extensive interest is focused on vanadium oxides mainly for their structural diversity and potential applications in various domains as for instance, heterogeneous catalysis, cathode materials for advanced lithium batteries, visible light photochromism and electro-chromic devices. In this specific context that associates an extrusion process with vanadium oxide gel, first vanadium oxide macroscopic fibers have been generated[5] with longitudinal Young modulus around 15 GPa that corresponds to the values obtained for carbon nanotube fibers. These fibers allow fast cycling insulator-semiconductor properties directly related respectively to the absence or presence of an alcohol vapor source, acting so as a highly sensitive and fast alcohol micro-sensor. Beyond, by tuning the shear imposed to the extruded ribbon used as nanobuiliding blocks, the fibers sensing and mechanical properties can be tuned on demand.[6] Also, the effects of latex nano-inclusions and induced nanoporosity over the mechanical and sensing properties will be discussed. 1- R. Backov, Soft Matter, 2006, 2, 452. 2- F. Carn, A. Colin, M.-F. Achard, H. Deleuze, E. Sellier, M. Birot, R. Backov J. Mater. Chem., 2004, 14, 1370. 3- F. Carn, A. Colin, M.-F. Achard, H. Deleuze, C. Sanchez, R. Backov Adv. Mater., 2005, 17, 62. 4- F. Carn, A. Colin, M.-F. Achard, H. Deleuze, R. Backov Adv. Mater., 2004, 6, 140. 5- L. Biette, F. Carn, M. Maugey, M.-F. Achard, N. Steunou, J. Livage, R. Backov Adv. Mater., 2005, 17, 2970. 6- H. Serier, M.-F Achard, N. Steunou, J. Maquet, J. Livage, O. Babot, R. Backov. Adv. Funct. Mat., 2006, 16, 1745.


4:15 PM V2.8
Gas Sensing Properties of MoO₃ Nanoparticles and Nanowires. Lisheng Wang, Krithika Kalyanasundaram and Perena Gouma; Department of Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, New York.

Molybdenum trioxide (MoO₃) is one of the most promising semiconducting metal oxide materials for functional applications. In this article, two morphologies of MoO₃ nanostructures, including nanoparticles and nanowires were successfully synthesized by sol-gel method and electrospinning method, respectively and then characterized by SEM, TEM and XRD. Gas sensing properties of both products to NH₃ have been measured, indicating that they can detect NH₃ with the concentration down to ppb level with fast response. In addition, responses to other gas exposures including NO₂, NO and CO, have also been detected and the sensing properties to them were compared. Emphasis is paid on the effect of humidity to the gas sensing response of these materials and the relative stability of nanoparticles vs nanowires structures.


4:30 PM V2.9
Hydrogen Detection using NEMS Devices Fabricated from Tunable Microstructure Pd-Ta Nanocomposites. David Mitlin¹, Chris Gilkison¹, Kenneth Bosnick⁴, Colin Ophus¹, Christopher Harrower¹, Reza Mohammadi¹, Ken Westra², Zonghoon Lee³, Ulrich Dahmen³ and Velimir Radmilovic³; ¹Chemical And Materials Engineering and National Institute for Nanotechnology, University of Alberta and NRC, Edmonton, Alberta, Canada; ²Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada; ³NCEM, Lawrence Berkeley National Laboratory, University of California, Berkeley, California; ⁴National Institute for Nanotechnology, NRC, Edmonton, Alberta, Canada.

Macro and micro-scale portable Pd-based resistive hydrogen sensors are considered an established technology. However, because hydrogen needs to both dissociate at the Pd surface and diffuse into the material in a significant quantity, existing portable Pd sensors suffer from relatively slow response times coupled with the requirement of high hydrogen partial pressures for detection. The difficulty in achieving nano-scale sensors, which are intrinsically faster and more sensitive, is related to the difficulty of reproducibly depositing, patterning, etching and releasing very thin Pd lines that have much higher surface to volume ratios. We have developed a family of new thin films based on the Pd-Ta system that have an amorphous-nanocrystalline microstructure. This microstructure is unique and results in materials with exceptional properties including little or no deposition shadowing effects, near atomic level smoothness, very high nanoindentation hardness, zero deposition stress, a tunable elastic modulus, metallic conductivity and the ability to still dissociate and absorb hydrogen. These unique features have allowed us to fabricate resistive hydrogen sensors with nano-scale width and thickness, but a meter-scale total length, all contained within a micron scale device on a silicon substrate. The combination of a short diffusion length and ultra-high surface to volume ratio has resulted in exquisite detection sensitivity and a very fast response time. The sensors are strong enough to be released from their substrates, effectively doubling their surface area to volume ratio, and could also be fabricated into released multilayer stacked arrays. We were also able to employ these alloys to fabricate the first generation of fully released single-anchored nanometer-scale cantilevers, to be used in both static and resonance gas detection mode.


SESSION V3: Poster Session: Functional Materials for Chemical and Biochemical Sensors I
Chairs: Vincenzo Guidi and Xiao-Dong Zhang
Tuesday Evening, April 10, 2007
8:00 PM
Salon Level (Marriott)

V3.1
BaZrO3 Thin Films for Humidity Gas Sensors. XiaoXin Chen, Michael Sorenson, Clayton Butler, Loren Rieth, Mark Miller and Florian Solzbacher; University of Utah, Salt Lake City, Utah.

Microscale (MEMS) gas sensing devices based on transition metal oxides for power plant exhaust gas streams are being developed. Reliable measurement of the target exhaust gases will have great benefits for power plant controls and exhaust gas remediation. Bulk BaZrO3 has been previously found to be sensitive to H2O at high temperatures, but was never studied in a thin film form. This research thrust focuses on undoped BaZrO3 and doped BaZrO3 with Y. Thin films were deposited on oxidized n-type silicon substrates at room temperature from ceramic targets with an Ar sputtering ambient. Various deposition pressures and deposition powers were used for the initial investigation. The structural and electrical properties of the deposited films were characterized to investigate their relationships to the deposition process parameters. X-ray diffraction (XRD) was used to measure the crystal structure of the deposited films, and in particular was used to determine if any crystallographic texture is present in the films. XRD results indicate the as-deposited films are amorphous before annealing. Films sputtered with and without oxygen in the ambient were compared. The crystal structure and morphology of BaZrO3 and BaZrO3 doped with Y after annealing were also determined. The materials changed from amorphous to crystalline after annealing at temperatures of 800 °C and 1000 °C for 3 hours in forming gas (2% H2 balanced with Ar gas). Temperature was found to dominate over deposition conditions in determining the final film structure. Atomic force microscopy was used to examine the morphology of the thin films. Gas sensor test structures using a Pt thin film metallization for interdigitated electrode structures were fabricated for gas sensing measurements. The experiments with the completed test structures measured the materials’ resistivity as a function of temperature and gas concentration. Both materials decrease in resistance with increasing temperature, which is consistent with ionic conduction. Some experiments tested the gas sensitivity and selectivity of the films to the target gas H2O vapor (humidity) and possible cross sensitive gases H2 and CO2. Both materials need further development to evaluate their suitability for thin film sensors. First, the films were found to be highly resistive, making characterization of the electrical properties very difficult. Second, O2 ambient annealing gas will be applied to compare the crystal structure and morphology of both films with an Ar ambient annealing process. Besides crystallizing the films, the annealing process also caused cracks to form in some thicker films. Two possibilities could cause the cracks. One is thermal stress during the annealing process and the other is because of its own material stress.


V3.2
Abstract Withdrawn

V3.3
Designing Chemo-Sensors based on Charged Derivatives of Gramicidin A Ricardo F Capone¹, Steven Blake², Thomas Mayer¹, Marcela Rincon Restrepo¹, Jerry Yang² and Michael Mayer¹; ¹Biomedical Engineering, University of Michigan, Ann Arbor, Michigan; ²2Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, Colorado.

Chemical changes of charge at the entrance of modified gramicidin A (gA) pores can be used to monitor chemically reactive agents with sensitivity up to individual molecules Ref. Here, we discuss the relevant parameters to optimize the sensitivity of such ion channel-based sensors. In order to design an effective sensor that measures changes in charge of a gramicidin A pore, the following conditions should be fulfilled: 1) the synthesis of the sensor (i.e. the derivative of gA) should be simple, practical, and start from readily accessible molecular building blocks; 2) the charge should be placed as close to the entrance of the pore as possible to achieve high sensitivity; 3) the total charge on the gA derivative should be well-defined within the operational pH range; 4) the ionic strength of the recording buffer should be as low as possible while maintaining a detectable flow of cations through the pore (≤ 0.1 M); 5) the applied transmembrane voltage should be a high as possible (> 100 mV); 6) the lipids in the supporting membrane have to be charged differently than the derivative of gA to avoid shielding; and 7) folded bilayers as opposed to painted bilayers should be used. Measuring the single channel conductance of gA derivatives under these optimized conditions showed that, the difference in ion channel conductance of neutral and negatively charged derivatives of gA depends only on the charge at the entrance of the pore; it does not depend on the charge at the exit of the pore. This asymmetric characteristic opens the possibility to design bi-functional sensors that detect the presence or absence of a charge on each monomer of a functional gA pore independently.


V3.4
Integrated Optical Sensing with Desorption Ionization Mass Spectrometry on Chemically Modified Porous Silicon Photonic Crystals Kristopher Alan Kilian¹, Russel Pickford³, Suhrawardi Ilyas², Katharina Gaus⁴, Michael Gal², Michael Guilhaus³ and J. Justin Gooding¹; ¹School of Chemistry, University of New South Wales, Sydney, New South Wales, Australia; ²School of Physics, University of New South Wales, Sydney, New South Wales, Australia; ³Bioanalytical Mass Spectrometry Facility, School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia; ⁴Centre for Vascular Research, School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia.

New methods in mass spectrometry employing solid substrates that assist ionization show promise for small molecule profiling in biology and medicine. Desorption ionization on porous silicon (DIOS) mass spectrometry in particular has been widely utilized owing to a high surface area and matrix-free ionization. Porous silicon based photonic crystals have been used extensively as biosensing transducers but no reports on their integration into DIOS applications have been made. In this work we show detection of peptides on two different optical crystals, microcavities and rugate filters. The structure and optical properties of the crystals are easily tuned during fabrication by modifications to the applied current density, yielding a mesoporous scaffold that exhibits a resonance in the reflectivity spectrum upon incident light irradiation. Introduction of peptides results in a change in the resonant reflectivity position proportional to the change in refractive index. The ionization of peptides from the porous materials is shown to depend on both the nanostructure and surface chemistry. Two different chemical strategies, employing alkene hydrosilylation were compared for their effect on peptide ionization and detection sensitivity. Hydrophobic monolayers were found to yield greater sensitivity to peptide compared to hydrophilic layers. The thickness of the porous structure was found to be critical in the ability of peptide to be ionized in the absence of matrix. The integration of silicon-based photonic sensors with mass spectrometry will enable optical detection of captured molecules and subsequent quantitative analysis, eliminating sample processing steps and providing “smart” analytical components.


V3.5
Abstract Withdrawn


V3.6
Abstract Withdrawn


V3.7
Abstract Withdrawn


V3.8
Optical Resonant Cavity to Detect Chiral Media. Riccardo Milan^1,2, Vincenzo Guidi^1,3 and Sergei Atutov^1,3; ¹Dept. of Physics, University of Ferrara, Ferrara, Italy; ²National Laboratory of Legnaro, INFN, Legnaro (PD), Italy; ³INFN, Ferrara, Italy.

The presence of chiral substances (CS) is important since it could cause some disease like diabetes, it regulates the goodness of some foods like vaccine milk, the health state of particular subjects in presence of drugs or dopant in their blood and it allow the study of Dna. Otherwise the chemical detection of these substances is not simple: the chiral solution reacts only with a chiral agent like an enzyme. An useful chiral agent is the circularly polarized wave in fact it travel through the chiral media with different velocity according to its helicity. Linearly polarized wave, superposition of two circularly polarized waves, travelling though chiral media, emerges with plane of polarization rotated due to the interaction with the medium. It suggests an elegant method to investigate this media based on optical device. A proposal for a Fabry Pérot interferometer (FPI) sensitive to chiral solutes in liquid solutions has been developed. A Fabry-Perot interferometer (FPI) is structured that as a pair of high-reflective mirrors at opposite ends of a cavity. Light reflects back and forth between the mirrors through a small part of that emerges for analysis through one of the mirrors. A typical spectrum of a FPI consists of a series of equally spaced peaks in the frequency domain pertaining to the frequency with which the optical cavity is resonant. We verified that a FPI filled with chiral media presents the spectrum of transmitted components with the peaks splitted in two equal parts. We analyze the normal incidence configuration of light on the strength of major experimental advantage in the alignment of the mirrors. In this configuration there is a problem of compensation of optical activity and we study a possible compensation of this phenomena. The simulations allow to verify the high sensitivity of this device with different chiral parameters and different reflectivity of mirrors. In the experimental analysis we work out with different media inside the cavity: air to align the mirrors, water to verify the operation with a liquid between mirrors (not trivial operations) and finally a chiral solvent into water. We obtain encouraging results of an experimentally achieved spectrum with a solution of 1%-saccarose. We observed split in the spectrum according to theoretical predictions.


V3.9
Abstract Withdrawn


V3.10
Air Reference Free Miniaturized Oxygen Sensor for Combustion Applications. John V. Spirig¹, Prabir K Dutta¹, Jules L Routbort² and Dileep Singh²; ¹Chemistry, The Ohio State University, Columbus, Ohio; ²Argonne National Laboratory, Argonne, Illinois.

Potentiometric internal reference oxygen sensors are created by embedding a metal/metal oxide within a yttria-stabilized zirconia oxygen-conducting ceramic superstructure. Three metal/metal oxide systems based on Pd, Ni, and Ru are examined. A static internal reference oxygen pressure is produced inside the reference chamber of the sensor at the target application temperature. The metal/metal oxide-containing reference chamber is sealed within the stabilized zirconia ceramic superstructure by a high pressure (3-6MPa) and high temperature (1200-1300dC) bonding method that initiates grain boundary sliding between the ceramic components. The bonding method creates ceramic joints that are pore-free and indistinguishable from the bulk ceramic. The Pd/PdO-based oxygen sensor presented in this study is capable of long-term operation and resistant to the strains of thermal cycling. The current temperature limit of the device is limited 800dC. As the sensor does not require reference gas plumbing there is flexibility in placement of sensors in a combustion stream. Furthermore, the sensor assembly process readily lends itself to miniaturization.


V3.11
Studies of TiO2 Based Mixed Oxide Thin Film Materials Prepared by Ion-assisted Electron Beam Evaporation for Gas Sensing Applications. Anurat Wisitsoraat¹, Elisabetta Comni², Giorgio Sberveglieri², Wojtek Wlodarski³ and Prayoon Songsiriritthigul⁴; ¹Nanoelectronics and MEMS Laboratory, NECTEC, Bangkok, Thailand; ²Sensor Laboratory, University of Brescia, Brescia, Italy; ³School of Electrical & Computer Engineering, RMIT University, Melbourne, Victoria, Australia; ⁴National Synchrotron Research Center, NakhonRatchasima, Thailand.

TiO2 is one of the most promising gas-sensing materials due to its high temperature stability, and harsh environment tolerance. However, its low electrical n-type conductivity hinders its practical implementation as a conductometric sensor. The addition of foreign atoms into TiO2 host is one of the most effective means to improve its conductivity as well as gas-sensing selectivity. In this report, various TiO2 mixed thin film materials prepared by ion-assisted electron beam evaporation have been studied for gas-sensing applications. First, four TiO2 composites, TiO2-WO3, TiO2-MoO3, TiO2-NiOx, and TiO2-ZnO, are made by thorough mixing of TiO2 powder with WO3, MoO3, NiOx, or ZnO powders with different concentrations ranging from 1% to 20 %. The mixed powders are then compressed into pellets and the compressed materials are electron beam evaporated with oxygen ion-addition to form TiO2 nanocomposite thin film on glass, silicon, and alumina substrates. Chemical, structural, and morphological characterizations have been performed by means of photoemission techniques, X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Atomic force microscopy (AFM). After annealing in air at 500 deg C, AFM, SEM, and XRD characterizations reveal that various TiO2 thin films have nanocrystalline structure with fine grain ranging from 10-50 nm. In addition, different surface morphologies have been observed. It is found that MoO3 and ZnO inclusions produces precipitates or bright particles on the surface while no such precipitate is formed on TiO2-WO3 and TiO2-NiOx thin film. Photoemission techniques, including X-ray and Ultraviolet photoemission spectroscopy (XPS and UPS) confirms expected elemental composition of Ti, O and addition elements of W, Mo, Ni, Zn on the thin film surface. Furthermore, the oxidation states of these metallic elements has been identified. Electrical and gas-sensing characterizations toward different gases including acetone, CO, and NO2 have been carried out. From electrical characterization, NiOx addition with sufficiently high concentration has proven to produce p-type semiconducting thin film while WO3, MoO3, and ZnO inclusions result in typical n-type metal oxide semiconductor. The gas-sensing sensitivity, selectivity, and minimum detectable concentration can be effectively controlled by different dopants and doping concentrations. WO3 doped TiO2 thin film showed high sensitivity towards NO2 acetone and ethylene at lower working temperature. In addition, TiO2-MO3 material demonstrated good sensitivity towards CO. But ZnO inlcusion deteriorated sensitivity towards all gases. While p-type NiOx doped TiO2 structure show high sensitivity toward ethanol and acetone with distinct behaviours compared to other n-type TiO2 thin films.

V3.12 TRANSFERRED TO V1.5

V3.13
Abstract Withdrawn


V3.14
Gold-Tantalum Nanocomposite as Structural Material for Resonant NEMS Biosensing Cantilevers. N. Nelson-Fitzpatrick¹, C. Ophus², E. Luber², L. Gervais¹, D. Mitlin², Z. Lee³, V. Radmilovic³, U. Dahmen³ and S. Evoy¹; ¹Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada; ²Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada; ³National Center For Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California.

The application of micro-electro-mechanical-systems (MEMS) and nano-electro-mechanical-systems (NEMS) to chemical and biological sensing has been the focus of substantial work in the scientific and engineering fields. Most MEMS and NEMS devices are fabricated from single crystal or polycrystalline silicon, carbides, nitrides or diamond films, with silicon being the most commonly employed [1]. The selective immobilization of molecular species onto device surfaces is however key to the successful development of any given biosensing platform. One method that has been proposed for the biofunctionalization of NEMS devices is to synthesize thiolized molecules that will bind to a biological system of interest, and to exploit the natural affinity of such molecules for a gold structure that has been deposited onto the device [2]. Such steps however introduce additional fabrication complexities for the realization of the device. It has also been shown that the deposition of metal onto a dynamic NEMS device significantly degrades the quality of its resonance [3]. Nanomechanical resonating biosensors could alternatively be machined directly out of a gold material, allowing the direct use of thiol-based chemistry for their biofunctionalization. Metallic materials have however mostly been overlooked given their limited stiffness and hardness, as well as the challenge associated with the nanomachining of a traditionally polycrystalline system. To that end, we have synthesized a series of nanocomposite alloy films of Gold-Tantalum at different stoichiometries using a co-sputtering method. These Au-Ta films feature significantly reduced grain size, as low as 40nm average diameter for a 400nm-thick film, and a roughness of less than 1nm RMS. Additionally, we were able to tune intrinsic stress and control the elastic modulus by varying the Ta concentration in the alloy. All these mechanical and physical improvements were achieved without the loss of the film’s affinity towards thiolized molecules. We have fabricated a series of resonant ultra-thin resonant cantilevers with lengths ranging from L = 1 to 8 um, widths ranging from W = 400 to 800nm, and a thickness of T = 50nm out of low stress Au-Ta (5at. % Ta). These devices possessed resonant frequencies ranging from f = 500 kHz to 10 MHz. From these results, we extracted a root of modulus to density ratio of (E/ρ)^0.5 = 2490 m/s. We will present a full description of the mechanical properties of this alloy as function of its composition. We will also present preliminary results on the binding of thiolized self-assembled monolayers and bacteriophages onto these ultra-thin Au-Ta cantilevers. [1] D. W. Carr, S. Evoy, L. Sekaric, J. M. Parpia, and H. G. Craighead, Appl. Phys. Lett. 75, 920 (1999). [2] B. Ilic, S. Krylov, W. Senaratne, C. Ober, P. Neuzil, and H. G. Craighead, J. Appl. Phys. 95, 3694 (2004). [3] L. Sekaric, D.W. Carr, S. Evoy, J.M. Parpia, HG Craighead Sens & Act. A 101, 215 (2002).


V3.15
Abstract Withdrawn


V3.16
Conjugated Polyelectrolyte Sensors Kirk S. Schanze, Chemistry Department, University of Florida, Gainesville, Florida.

Conjugated polyelectrolytes (CPEs) are pi-conjugated polymers such as poly(phenylene vinylene) (PPV) and poly(phenylene ethynylene) (PPE) which contain ionic side groups. CPEs are soluble in polar solvents, including water, and they are highly fluorescent. We have demonstrated that charged quenchers such as N,N’-dimethyl-4,4’-bipyridinium (MV2+) or anthraquinone sulfonate quench the luminescence from oppositely charged CPEs with extremely high efficiency. Stern-Volmer constants as large as 1E+08 M-1 have been observed in specific systems. This interesting “amplified quenching” effect is believed to arise due to ion-pairing between the quencher and the CPE, coupled with the ability of the exciton to rapidly diffuse along the polymer chain(s). Amplified quenching provides the basis for application of CPEs in biosensors which are able to detect targets such as proteins, peptides and carbohydrates. The presentation will overview our work in this area, with specific examples provided for biosensors for specific protease and phospholipase enzymes. Leading References Pinto, M. R.; Schanze, K. S. Proc. Natl. Acad. Sci. U.S.A. 2004, 7505-7510. Zhao, X., et al. Macromolecules 2006, 39, 6355-6366.


V3.17
One-dimensional Photonic Crystals Based on Functional Ordered Mesoporous Films. Hernan Miguez¹, Maria Cecilia Fuertes², Francisco Javier Lopez-Alcaraz¹, Galo Soler-Illia², Paula Angelome² and Victor Luca³; ¹Institute of Materials Science of Seville, Spanish Research Council, Sevilla, Spain; ²Centro Atómico Constituyentes, Comisión de Energía Atómica, San Martín, Argentina; ³Institute of Materials and Engineering Sciences, Lucas Heights, New South Wales, Australia.

The possibility of obtaining optical quality materials presenting well defined and tuned pore arrays with controlled functional surfaces and precise spatial location in several length scales has opened the path towards “intelligent surfaces”. A number of strategies have been developed to create mesoporous films (MPF) with a variety of oxide frameworks, compositions, organic functions, etc.(1) The field is mature enough to reproducibly create monolayer MPF with well defined desired features in the mesoscopic or molecular scales. MPF represent thus “functional building blocks” for the construction of complex architectures, which can give access to new properties arising from order in space at different length scales. An interesting example is to combine order at the mesoscale and at the submicronic scale, which can lead to new optical responsive materials. We demonstrate that ordered mesoporous thin films can be used as building blocks to construct one-dimensional photonic crystals, also known as optical Bragg reflectors, of high optical quality and with a selective optical response to the environment.(2) These structures are made by alternate deposition of mesoporous slabs of two different compositions and combine properties due to the periodic structuring at different length scales. The highly controlled porosity stemming from periodicity in the mesoscale permits to tailor the interaction with small molecules that can adsorb or even condense in the surface or pore system of the inorganic matrix, leading to a sensitive and reversible change in the optical Bragg diffraction position. Optical quality and the effect of functionalisation are assessed by optical transmission and reflection measurements in the visible range of the ordered mesoporous Bragg reflectors exposed to different treatments and environments. The optical response of these coloured mesoporous multilayers in the presence of molecules that adsorb on the pore surface can be tuned through the selective introduction of functional groups in just one type of the building blocks of these structures. Furthermore, the introduction of MPF with adequate thickness/refraction index in particular positions in the stack leads to controlled defects and the appearance of allowed states in the gap. We demonstrate that combination of the controlled deposition of templated films and selective surface functionalisation results in complex hierarchical materials with photonic crystal properties, which are potentially useful for optical sensing or smart windows with environment-modulable properties. (1) G.J.A.A. Soler-Illia, P. Innocenzi, Chem. Euro. J., 2006, 12, 4478 (2) M.C. Fuertes, F.J. López-Alcaraz, M.C. Marchi, H. E. Troiani, H. Míguez, G. J. A. A. Soler-Illia, Adv. Mater. Submitted.


V3.18
Thermal and Mechanical Stability of Directly Deposited, SiO₂-doped SnO₂ Sensor Layers Antonio Tricoli and Sotiris E. Pratsinis; Particle Technology Laboratory, Mechanical and Process Engineering, ETH Zurich, Zurich, Switzerland.

Direct deposition of nanoparticles on sensor substrates avoids the tedious steps of standard routes of wet synthesis of nanoparticles and their slurry or paste deposition and subsequent solvent evaporation and calcinations that frequently results in layers with non-reproducible sensor performance because of cracks and other imperfections during layer synthesis. Despite their promise, direct deposition techniques suffer from limited layer adhesion and cohesion to the substrate stemming from their high porosity. This defect prevents the immediate scale-up and compatibility of direct deposition techniques with CMOS technology for manufacture of sophisticated sensors. Here, lacy, nanostructured, pure or SiO₂-doped SnO₂ layers of high porosity (98%) are self-assembled on SiO₂ or SiN substrates. Doping with SiO₂ is investigated by morphological and thermal stability analysis by BET, XRD, HR-TEM, STEM and EDXs. The SiO₂ presence reduced thermally-induced growth up to 900 °C, stabilizing crystal size at 18 and 7 nm respectively by 0.8 and 8 wt % while preserving sensor high sensitivity. Preliminary experiments on SnO₂/SiO₂ nanomaterial synthesis revealed formation of crystalline SnO₂ and well dispersed amorphous SiO₂. Addition of SiO₂ strongly increased SnO₂ thermal stability already at 0.8 wt % due to the good SiO₂ dispersion. Increasing SiO₂ mass up to 8 wt % did not produced fully coated SnO₂ particles preserving the SnO₂ nanoparticles’ good sensitivity. Functionalization with SiO₂ is particularly promising for sensor application in harsh environments, granting good sensor material stability at high sensitivity. Estimation of layer adhesion is quantitatively determined by measuring the area cleared below N₂ jet gas and water impingement test experiments. The sensor performance is established for CO and ethanol (EtOH).


V3.19
A Facile Synthetic Route to Produce Indium Oxide Nanostructures. suitable for gas sensor applications Dae Joon Kang^1,2,3 and Jimin Du^1,2,3; ¹Physics, Sungkyunkwan University, Suwon, South Korea; ²SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon, South Korea; ³Institute of Basic Science, Sungkyunkwan University, Suwon, South Korea; ⁴Center for Nanotubes and Nanostructured Composites, Sungkyunkwan University, Suwon, South Korea.

Colloidal nanocrystals with controlled sizes and morphologies play a key role in nanotechnology due to their tuning capability required for the development of novel optical, electrical, catalytic and sensing applications. Among them, Indium oxide (In2O3), one of the most important n-type wide-band gap (3.5-3.7 eV) semiconductors, has become very attractive recently because it offers technological advantages over other similar material systems in optoelectronic devices and gas detectors owing to its high electrical conductivity, high transparency to visible light, and the strong interaction between certain poisonous gas molecules and In2O3 surfaces. Hence, several synthetic methods such as chemical vapor deposition (CVD), surfactant-induced chemical method and electrical chemistry have been reported to prepare In2O3 nanomaterials with a desired motif required for viable industry applications. Although the technology to control the size and the size distribution of nanomaterials is reasonably well developed, reports on the systemic synthesis of complicated nanostructures, however, are very few. In our work, a simple chemical synthetic route is developed to produce various In2O3 morphologies such as nanofloweres, nanospheres, nanorods, and nanocubes by adding different surfactants. For example, In2O3 nanoflowers can be synthesized by performing experiments with reaction precursors of In(acetate) (40 mg) and ethylenediamine (2 mL) in ethanol (10mL) at 240 oC and remained for 18 hrs. As confirmed visually by SEM, monodispersed nanoflowers with diameter of about 100 nm can be obtained with a high yield. Interestingly, when the amount of ethylenediamine is reduced to be 1mL while other reaction conditions were kept the same, it was found that the In2O3 nanospheres with the size of 200 nm are formed with a high yield. Further reducing the amount of ethylenediamine to 0.5 mL results in the irregular nanoparticles while other reaction conditions are kept the same. Moreover, when the oleic acid (1 mL) is used instead of ethylenediamine, the nanorods are formed with the diameter of about 30 nm and the length of over 100 nm. In addition, when acetic acid is used instead of oleic acid, the In2O3 nanocubes are formed with the size of about 400 nm. Based on the results obtained here, surfactant-induced chemical method can be proposed to account for the growth of In2O3 nanostructures with various morphologies under similar experimental conditions. These In2O3 nanomaterials with various morphologies can be exploited easily to fabricate gas sensors, for instance, suitable for NO2 by deposition of the as-synthesized samples onto alumina substrates.


V3.20
Control of Cell Adhesion Using Conducting Polymers Maria H Bolin¹, Karl Svennersten², Emilien Saindon¹, Agneta Richter-Dahlfors² and Magnus Berggren¹; ¹Organic Electronics, Science and Technology, Linköping University, Norrköping, Sweden; ²Department Of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, Sweden.

Petri dishes of polystyrene and plastic foils were coated with the conducting polymer PEDOT (poly (3, 4-ethylenedioxythiophene)), via an all-liquid chemical polymerisation process including iron (III) tosylate as the counter ion. The polymer surface is then subtractive patterned to form adjacent electrodes using over-oxidation as the patterning technique. This enables us to exclusively address and reduce one PEDOT-electrode while the other is oxidized and cell media serve as the electrolyte. We have investigated how cells adhere, grow and differentiate onto the two electrodes while they are biased with an appropriate electric signal. Epithelial MDCK cells have been seeded on the surfaces on both pristine PEDOT surfaces and on pre-switched surfaces. We find that cells that were seeded on a pre-switched surface and incubated showed a distinct difference of adhesion and growth character on the two different electrodes, depending on the bias voltage. The cells prefer to adhere to the reduced side while hardly any cells were found on the oxidized electrode. We also found that cells that initially adhered to the reduced side starts to release when the surface was switched from the neutral state to the oxidized side. The surfaces can be switched reversibly to generate full adhesion-release cycles of the cells. Electrochemically active surfaces can be included in electrochemical devices, such as transistors. Our findings open for complex circuits carrying surface switches that allow us to, via electronic x-y-addressing control the cell adhesion and growth along large surfaces. Such “smart” surfaces can be used to guide cell growth to form desired tissue formation, to control cell culturing in general, to electrically control the release of large cell membranes etc.


V3.21
Plasma Polymer Nanocoatings as Responsive Materials for Ultrasensitive Sensor Platform. Srikanth Singamaneni^1,2, Melburne LeMieux⁴, Michael McConney^1,2, Yen-Hsi Lin^2,4, Hao Jiang³, Jesse O Enlow³, Timothy J Bunning³ and Vladimir V Tsukruk^2,1; ¹Polymer, Textile and Fiber Engineering, Geogia Institute of technology, Atlanta, Georgia; ²School of Materials Sceince and Engineering, Georgia Institute of Technology, Atlanta, Georgia; ³Materials and Manufacturing Directorate, Air Force Research Laboratory, Wight-Patterson Air Force Base, Ohio; ⁴Department of Materials Science and Engineering, Iowa State University, Ames, Iowa.

Bimorph microcantilever structures have been introduced as a novel sensing approach exploiting interfacial stresses. We demonstrate that silicon cantilevers coated with plasma polymerized nanolayers on one side can be employed as highly sensitive physical and chemical sensors. The actuation in response to the external stimuli is caused by the differential interfacial stress of the bimorph structure due to the responsive residual stresses in the polymer layers. The polymer layers undergo structural changes in response to external stimuli resulting in internal stresses (on the order of MPa) sufficient to induce huge interfacial stress. Bimorph structures has been applied to develop uncooled IR sensors with unprecedented sensitivity (2nm/mK) and vapor sensors with high sensitivity (200 ppt) and excellent dynamic response on the order of several msec. The technology demonstrated here can be extended for developing a new class of trace detectors with a wide range of applicability in chemical and biological sensing.


V3.22
Polymer Nanocomposite Based Chemiresistive Gas Sensors. Divakara Atchuta B.S. Meka¹, Shalini Prasad¹ and Linda George²; ¹Electrical and Computer Engineering, Portland State University, Portland, Oregon; ²Environmental Science, Portland State University, Portland, Oregon.

We present here the development of a polymer nanocomposite based gas sensor for detecting trace gas emissions in ambient environment. The principle of measurement of these nanomaterial devices, known as chemiresistive sensors, is through resistance changes associated with the selective reaction of gaseous agents onto the nanomaterial matrix. These gas sensors function on the chemiresistive principle-variations in the resistance of a trace gas sensitive polymer encapsulated active sensing element comprising of carbon nanoparticles is observed due to the selective reaction of the reactive gases. In contrast to the current techniques in gas sensing, the technique that is under development has a simple photolithography based fabrication scheme that can be executed on a non specialized wet bench, thus is less expensive, highly reproducible and robust. For the current application, the sensor characteristics will be demonstrated for nitrogen dioxide (NO2). Existing chemiresistive sensors are limited in sensitivity and selectivity. The goal of this project is to achieve dramatic improvements in sensor sensitivity and specificity through innovative functionalization and packaging of nanomaterial sensors. The goal of this project is to improve sensitivity for carbon-based nanomaterial sensors from parts-per-million (ppm) levels to parts-per-billion (ppb) under real world levels of air contaminants.


V3.23
Immobilization of Glycine and its Oligomers on Aldehyde-terminated Surfaces and its Influence on the Orientation of Liquid Crystals. Kun-Lin Yang and Xinyan Bi; Chemical and Biomolecular Engineering, National University of Singapore, Singapore, Singapore.

This presentation reports an investigation of the immobilization of glycine (gly) and its oligomers, gly-gly and gly-gly-gly on silica substrates decorated with aldehyde functional groups. It is found that the density of glycine and its oligomers immobilized on the surface can be greatly enhanced by using higher ionic strength (~ 1 M) and a reaction temperature of 50οC. It is also found that when a thin layer of nematic liquid crystal 4-pentyl-4’-cyano-biphenyl (5CB) was supported on a glycine or oligopeptide-decorated surface, the orientation of 5CB changed from planar to homeotropic over a period of 24 h. Furthermore, the switching time decreased when the surface density of the oligomers was increased, and when the length of glycine oligomers was increased. This method also has good spatial resolution over a large area that permits the detection of several different glycine oligomers on the same surface.


V3.25
Cross Conjugated Water Soluble Poly (para-phenylenes): Towards the Versatile Chemo- and Biosensors. Hairong Li and Suresh Valiyaveettil; National University of Singapore, Singapore, Singapore.

We have designed, synthesized and characterized a novel class of thermally stable water soluble polymers featuring cross conjugated structures modified with bi-functional groups. All copolymers were characterized by means of FT-IR, GPC, 1H and 13C-NMR, UV-Vis, fluorescence spectroscopy. Photophysical properties showed collective responses from their respective conjugated segments as well as high bandgap, indicating the non-planarity of the polymer chains probably due to the effect of charged functional groups. Fluorescence studies showed that these polymers have good sensitivity to both cationic and anionic quenchers through fluorescence decay, with an average Stern-Volmer constant up to 106 M-1. Besides fluorescence quenching, shift of absorption and emission maxima upon addition of small molecules was also observed, probably due to the intermolecular charge transfer mediated by quencher induced aggregation. At high concentration of quenchers the visible precipitation occurred, resulting in collapse of the UV-Vis spectra. All polymers were able to form highly fluorescent, flexible, uniform and smooth thin films simply by evaporation. Hence by attaching cationic and anionic groups on a cross conjugated water soluble structure, a bi-functional CP system was developed for sensor and other potential applications.


V3.26
Abstract Withdrawn


V3.27
Microphotonic Cylinderical Waveguide Based Protein Biosensor Vijay Sekhar Reddy Kovvuri¹, Sudhaprasanna Kumar Padigi¹, Kofi Kasaante², Andres LaRosa² and Shalini Prasad¹; ¹Electrical and Computer Science, Portland State University, Portland, Oregon; ²Physics, Portland State University, Portland, Oregon.

We have developed a micro-photonic cylindrical waveguide for the detection and characterization of antibody-antigen binding. The cylindrical waveguides were fabricated using standard photolithography on photo-sensitive polymer. We have characterized the device using 632.8nm red laser. The waveguide was excited through an etched silica fiber tip. The measurement system comprised of lock-in amplifier and a chopper for providing the reference. The proteins that where characterized were: C-reactive protein and Myeloperoxidase. These proteins have been hypothesized to be clinically relevant in early detection of vulnerable cardiovascular plaque in the preioperative state. The response time of the sensor is on the order of milli seconds. These sensors were tested up to a detection threshold of 10ng/ml for the proteins. The experiments were repeated in triplicate, to establish repeatability and robustness in the detection process.


V3.28
Characterization of the Transient Response of Amperometric Electrochemical Microsensors Jin Zou and Mark Wagner; Sensorcon, Inc., Reading, Massachusetts.

Micromachining technologies offer the potential to reduce the cost and increase the performance of amperometric sensors for toxic gases such as NO2. The sensitivity and response rate of these sensors are dependant upon mass transport phenomenon, which is governed by the geometry and permeability of the materials used. We have demonstrated a new amperometric microsensor technology that uses deposited catalyst films and aqueous electrolytes for improved performance, and have developed a multiphysics numerical method for characterizing its transient response. Earlier work on similar sensors used PVD films on Nafion sheets, and identified the electrode perimeter/area ratio as a key contributor to the signal/noise ratio [1]. Common methods to improve sensitivity by using high surface area nanomaterials on the electrode can increase current output, but do not necessarily increase the signal/noise ratio. Previous models which are based primarily on observation only consider the diffusion effects of a sensor membrane, and do not couple the effects of mass consumption due to the electrochemical reaction [2]. The principle of operation of amperometric sensors is based upon the reduction or oxidation of the gas when it comes into contact with the electrode-electrolyte interface. This implies that the gas must transport through an electrolyte film to the electrode surface before it can react. Therefore, aqueous electrolytes are advantageous because they offer both high permeability and high ion conductivity. However, since it is difficult for micromachined gas sensors to accommodate liquid materials, most recent research efforts have focused on solid state solutions, which are often not based on traditional electrochemical methods [3, 4]. In order to accommodate liquid based electrolytes, these sensors must be integrated with packaging [5, 6]. This paper reviews our effort to characterize a new type of electrochemical microsensor for NO2. MEMS processing methods are used to create a sensor structure which is compatible with aqueous electrolytes. We present a multiphysics based numerical method which couples multi-step diffusion and electrochemical consumption, by coupling Fick’s law with Faraday’s laws to better characterize the time dependant transient response of the sensor. Experimental tests of the sensor verify the accuracy of the model. References: [1] G. Jordan Macclay, William J. Buttner, and Joseph R. Stetter, IEEE Transactions on Electron Devices, Vol. 35, No. 6, pp793-799 June 1988 [2] Si-Chung Chang and Joseph R. Stetter, Electroanalysis, 2 359-365, 1990 [3] X.Z. Ji, A. Zuppero, J. Gidwani, And G. Somorjal, Nano Letters, Vol 5, No.4, 753-756, 2005 [4] Xiao Z. Ji and Gabor A. Somorjai, J. Phys. Chem. B, 109, 22530-22535, 2005 [5] R.L. Smith and S.D. Collins, IEEE Trans. Electron device, Vol. 35, No. 6, PP.782-792, 1988 [6] D.L. Polla, Richard Muller, Richard White, IEEE Electron Device lett., Vol. 7 No4, pp254-256, 1986

SESSION V4: Biosensors and Hybrid Sensors I
Chairs: Guido Faglia and Xiao-Dong Zhang
Wednesday Morning, April 11, 2007
Room 2008 (Moscone West)
8:45 AM *V4.1
Development of Polymer-based Sensors for Detection of Sulfur Dioxide at ppm-Level Concentrations. Margaret Amy Ryan, Charles J. Taylor, Abhijit V. Shevade, Adam Kisor, Shao-Pin S. Yen and Margie Homer; Jet Propulsion Laboratory, Pasadena, California.

The electronic nose (ENose) under development at the Jet Propulsion Laboratory uses an array of polymer-carbon black composite sensors to monitor spacecraft cabin air quality in near-real-time. Earlier generations of the JPL ENose have been successfully tested using a variety of organic analytes, as well as ammonia and hydrazine [1]. The next generation ENose is currently under development for demonstration on-board the International Space Station in 2008. For this application, sulfur dioxide has been added to the target compound list owing to crew health considerations. Sulfur dioxide is a potential contaminant in the breathing air from lithium-thionyl chloride batteries used to power equipment in the crew habitat on ISS, and is toxic at ppm-level concentrations. NASA has set a monitoring target of 1 ppm at atmospheric pressure for this demonstration. In developing sensors with a sensitivity toward SO2, the ENose team has used a combination of molecular modeling and experimental approaches. In modeling, the methodology adopted involves calculating binding energies of SO2 with common classes of organic structures using quantum mechanical methods. These organic structures represent functional groups on polymers which may be used as the basis for polymer-carbon composite sensors. Binding energies indicate a candidate for SO2 detection would be a polymer containing amine functional groups. Reversible SO2 absorption by polymers has been previously reported in the literature [2-4]. Literature information combined with modeling led to the use of novel polymer-carbon black films for sulfur dioxide detection at low ppm-level concentrations. We selected two polymers to investigate, derivatives of linear and cross-linked poly-4-vinyl pyridine (P4VPY) and vinyl benzyl chloride (VBC) functionalized with various free-amine containing substituents. This paper will consider the response of polymer-carbon composite films to SO2 and to other chemical species of interest to NASA for crew habitat monitoring. When preparing new materials, variables that must be investigated include: sensitivity, selectivity reversibility, and ability of sensors to be regenerated after exposures to SO2. In order to screen candidate materials, experiments were carried out using microarrays with interdigitated electrodes and embedded heaters, as well as microhotplate sensors. The use of this sensing approach assisted with optimization of sensing parameters such as operating and regeneration temperatures, and carbon-black loading. [1] M.A. Ryan, et al., IEEE Sensors Journal, 4, (3) 337-347, 2004. [2] A. Diaf, J.L. Garcia and E.J. Beckman, Journal of Polymer Science, 53, 857-875, 1994. [3] M. Matsuguchi, et al., Sensors and Actuators B-Chemical, 77, 363-367 (2001). [4] E. Ranucci, et al., Polymers for Advanced Technologies 7, 529-535 (1996).


9:15 AM V4.2
Chemical Sensing Properties of Poly(methyl metacrylate)- TiO2 Nanocomposites. Gabriella Leo¹, Annalisa Convertino¹, Marinella Striccoli², Michela Tamborra³, Corrado Sciancalepore³, Maria Lucia Curri² and Angela Agostiano^3,2; ¹ISMN, CNR, Monterotondo Staz. (Roma), Italy; ²IPCF - sez. Bari, CNR, Bari, Italy; ³Dipartimento di Chimica, Università di Bari, Bari, Italy.

The growing demand of our society to detect and monitor gases and vapors for safety, health and environmental issues requires a high degree of innovation in sensor technology, which includes both the research development of novel sensing materials and the integration of original sensor architectures. Particular attention has been devoted to polymers as sensing materials for devices exploiting various transduction signals, such as optical, mechanical, electrical and thermal. Some recent results show that the presence of inorganic nanoparticles (NPs) causes a further modification of the sorption processes in a polymer matrix [1]. Indeed the interaction between the NP surface and the gas molecules can control the selectivity, rate and efficiency, of molecule adsorption in the nanocomposite. In addition, the high surface-to-volume ratio of NPs increases the number of active sites for interaction with the analytes. Hence, NP based polymer composites can address an innovative generation of chemical sensors combining the sensing abilities and the possibility of a versatile tailoring of the physical properties of the NP with the mechanical and/or optical responses related to the gas sorption processes of the polymers. In this work the sensing properties of Poly(methyl metacrylate) (PMMA) based nanocomposite have been investigated as a function of the shape (dot or rod), concentration and surface ligands (oleic and phosphonic acid) of the embedded TiO2 NPs. Colloidal chemical routes have been used to synthesize the TiO2 NPs with a high control on size, shape and crystal phase. The surface chemistry of the NPs has been modified by exploiting ligand exchange techniques. Thin films of TiO2 NP-PMMA nanocomposite deposited by spin coating on Si and glass substrates, have been investigated by Vis-NIR spectrophotometry in presence of organic vapors (acetone, ethanol). Films of PMMA composites based on commercial TiO2 NPs have also been prepared as comparison. The effects of the surrounding vapors on the nanocomposite thin films have been tested by reflectance measurements in the visible. The vapor sensing behavior of the PMMA nanocomposite have been estimated by measuring the degree of swelling, Dt/t, where t is the thickness of the film and Dt is the relative thickness variation, from the reflectance spectra measured before and after the vapor exposure. Indeed, when the organic vapors are adsorbed by the polymer matrix, a reversible shift of the fringe pattern has been observed in the reflectance spectra for the nanocomposite films due to the reversible film swelling. The overall results have indicated that, the different shape of the embedded NPs and the presence of the organic molecule layer coordinating the surface of the TiO2 NPs appear to be critical in the sensing process, by enhancing or inhibiting the swelling phenomenon of the nanocomposite, and by modifying the response time of the PMMA. [1] A. Convertino et al. Adv. Mater. 13, 1103, (2003).


9:30 AM V4.3
Porous Silicon Microcavity Coupled with Fluorescence Polymer as a Sensor for the Detection of Explosives Igor A Levitsky^1,2, William B Euler², Natalia Tokranova³ and Aimee Rose⁴; ¹Emitech, Inc., Fall River, Massachusetts; ²Chemistry, University of RI, Kingston, Rhode Island; ³College of Nanoscale Science and Engineering, University at Albany (SUNY), Albany, New York; ⁴ICx-Nomadics, Cambridge, Massachusetts.

Conjugated polymers entrapped in porous silicon (PSi) microcavities (MC) have been studied as optical sensors for low volatility explosives such as TNT. The fluorescence spectra of entrapped polymers was modulated by PSi MC via a spectral “hole” that matches the resonance peak of the PSi MC reflectance. Exposure of the PSi MC containing entrapped polymer to explosives vapor results in a red shift of the resonance peak and the spectral “hole”, accompanied by the quenching of the fluorescence. These sensors can work simultaneously in reflective and in fluorescence regime. Upon exposure to TNT vapor, fluorescence is attenuated differently at different wavelengths, as compared to the uniform quenching of polymers deposited on a flat substrate in a typical emissive chemosensor. Proposed new approach allows the introduction of an additional set of parameters (detection wavelengths) to uniquely characterize specific explosive vapors and their interferants that could be beneficial in the design of next generation sensor arrays for explosives detection.


9:45 AM V4.4
Towards poly(3,4-ethylenedioxythiophene)s-based Sensors: Conductimetric Responses in Aqueous Solutions. Hsiao-hua Yu, Emril Mohamed Ali, Hong Xie, Shyh-Chyang Luo and Jackie Y. Ying; Institute of Bioengineering and Nanotechnology, Singapore, Singapore.

Conductivity-based sensory devices built on electrically conducting polymers (ECPs) offer great promise for the detection of a wide variety of analytes because they provide greater current output compared to the amperometry-based devices. To apply these novel materials as biosensors, it is critical to design and synthesize ECPs that are stable and functionalized in aqueous solution, conjugate the bioprobes through side-chain functionalization, and discover the mechanism of perturbing the polymer conductivity from side-chain recognition. Poly(3,4-ethylenedioxythiophene)s (PEDOTs) are of particular interest due to their high stability in aqueous solutions, high conductivity and versatility for side-chain functionalization. In ECP films, intrinsic conductivity was increased or reduced by a variety of molecular mechanisms upon analyte binding, including analyte-induced reductions in conjugation length and segmental energy matching/mismatching from adjacent redox-active sites. Herein, we report the first example of conductimetric response from shifting the conductivity curve of the synthesized PEDOTs upon oxidative doping. Increased negative charge density surrounding the polymer backbone raises the energy barrier for the efficient migration of positive charge carriers. Hence, we have to apply a higher potential to overcome the conductive barrier. Notably, the conductivity maximum remained identical, and this phenomenon was performed and identified in aqueous solutions. One particular example involved the conductimetric response from the deprotonation of carboxylic acid functionalized PEDOTs, poly(EDOT-COOH)s. Applying 100-mV offset between two sets of working electrodes, the drain current that passed through poly(EDOT-COOH)-covered interdigitated electrode junctions started to increase when the potential applied was greater than -0.86 V in pH 4 buffer, indicating that the polymer became conductive upon oxidative doping. The current reached a plateau at -0.41 V. When subjected to a pH 7 buffer, a 200-mV anodic shift of the conductivity profile was observed. The control experiment of poly(EDOT-OH) displayed identical profiles at different pH’s. The Poly(EDOT-COOH)-coated electrodes were applied as resistive sensors for real-time measurements of the solution pH. This interesting phenomenon could pave the way to PEDOT-based biosensor applications in aqueous solutions.


10:30 AM *V4.5
Recent Advance on Chemical and Bio Sensors Using Oxide Nanowires and Carbon Nanotubes Chongwu Zhou, Dept. of Electrical Engineering, University of Southern California, Los Angeles, California.

In this talk I will present our recent advance on the chemical and biosensing applications of nanowires and carbon nanotubes. Single-crystalline oxide nanowires such as In2O3 and SnO2 were synthesized using a generic laser ablation method, and field effect transistors with on/off ratios as high as 104 were fabricated based on these nanowires. Furthermore, we have integrated nanowire chemical sensors with micromachined hotplates fabricated atop a silicon nitride membrane. This chemical sensor chip can be easily heated up to 400 degree and therefore allowed the study of chemical sensing at elevated temperatures. In2O3 nanowire sensors made this way exhibited good response to a variety of chemicals including ethanol, CO and hydrogen. Our devices exhibited significantly improved chemical sensing performance compared to existing solid-state sensors in many aspects such as the sensitivity, the selectivity, the response time and the lowest detectable concentrations. In addition, we have combined both In2O3 nanowires and carbon nanotubes for complementary detection of various biospecies important for biomedical research and environmental studies. One particular example is the detection of prostate specific antigen, an important biomarker for prostate cancer. While In2O3 nanowires showed enhanced conduction upon exposure, carbon nanotube transistors showed reduced conduction, as a result of the opposite polarity of carriers in these nanostructures. We have further developed a selective functionalization technique based on electrochemical activation and reduction between hydroquinone and quinine. This technique allowed us to functionalize an array of biosensors with different probe molecules, an important step toward the construction of biosensor chips. Our work clearly demonstrates the potential of one-dimensional nanostructures to work as high-performance


11:00 AM V4.6
Chemical Vapor Sensing with Novel Coupled Channel Organic Semiconductor and Silicon Field-Effect Devices. Deepak Sharma¹, Shannon Doane Lewis¹, Sebastian P. Schoefer¹, Ananth Dodabalapur¹, Myung Han Yoon², Antonio F. Facchetti² and Tobin J. Marks²; ¹Electrical and Computer Engineering, University of Texas at Austin, Austin, Texas; ²Department of Chemistry and the Materials Research Center, Northwestern University, Evanston, Illinois.

We report the characteristics of a new hybrid sensor device that combines the functional properties of silicon field-effect devices with unique properties of organic semiconductors and novel self-assembled dielectrics. The four-terminal field effect device has two channels: one formed in an organic semiconductor (p) and the second in silicon (n). Both the channels are coupled so that one channel gates the other. The organic channel is exposed to air and interacts with the chemical vapor present in the ambient. The device can operate as a traditional CHEMFET as well as an organic TFT based sensor. Another sensing mode, which is most sensitive, is designated as the chemical memory mode. In this unique mode of operation, the device operates in a manner akin to a non-volatile memory in which the write function is provided by the chemical analyte. The erase is done electrically by reverse biasing the device. In previous work, we reported on sensing characteristics of such devices with a thermally grown SiO₂ gate insulator coupling the two channels¹. In the present work, we couple the two channels through a high-k self assembled organosilane dielectric grown at Northwestern University. The relative dielectric constant is about 16. The typical thickness of this dielectric film is about 1.5-4 nm. This dielectric has recently demonstrated excellent properties in field-effect devices and combined a high dielectric constant, low leakage currents, and compatibility with a range of organic and inorganic semiconductors². In the chemical memory sensor mode, the n-channel is biased on while keeping the p-channel off and the n-channel current is measured with time. Subsequently, both the channels are biased on and conducting and analyte is delivered to the exposed pentacene layer. Following this, the n-channel current is measured again at the biasing condition prior to analyte delivery. The current increases by a a factor of about 5. This indicates a decrease in the threshold voltage (V_T) due to the hole trapping in the organic channel after the interaction with analyte. In these sensors we are essentially using trapped charges as the “non-volatile” gate charge. The charge retention requirements of the sensor are much less than that of a normal non-volatile memory. The reset mechanism is very similar- electrical reverse bias based resetting. The chief difference with established silicon CHEMFET technology is that CHEMFETs use channel charge modulation by dipoles (which have a net charge of zero) whereas in our device we use trapped positive charges which will obviously produce a much greater conductivity and capacitance modulation. 1. D. Sharma, L. Wang, D. Fine, and A. Dodabalapur, IEDM Technical Digest, 2005. 2. Myung-Han Yoon, Antonio Facchetti, and Tobin J. Marks. Molecular Dielectric Multilayers for Ulta-Low-Voltage Organic Thin Film Transistors, MRS Symposium Proceedings, 2005, 871E, I3.2.1-I3.2.6.


11:15 AM V4.7
Molecularly Imprinted Polymer-Based Immunoassay of Herbicide Acids Using Resonant Piezoelectric Membranes with Integrated Actuation and Read-Out Capabilities. Cedric Ayela¹, Fanny Vandevelde², Karsten Haupt² and Nicu Liviu¹; ¹Nanobiotechnology Department, LAAS CNRS, Toulouse, France; ²Universite de Technologie de Compiegne, Compiegne, France.

Molecularly imprinted polymers (MIP) represent a novel area of biomaterials that mimic the behaviour of natural antibodies exhibiting far greater stability than their natural counterparts. Even though their powerful interest has no more to be demonstrated for biological applications such as immunoassays or biosensors, the difficulty for commercial development of MIP may be due to their tough compatibility with standard immunoassay formats. Coupling silicon-based microfabricated structures with MIPs used as sensitive layer could overcome the main drawbacks of the latter ones by taking advantage of the high sensitivity and high resolution of the former ones. In this study, a MIP-based label-free immunoassay for the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is validated using piezoelectric circular micro-membranes working in dynamic mode. The membranes are circular shaped with a total radius equal to 100 µm. Each membrane can be individually actuated by a piezoelectric PbZrxTi1-xO3 (PZT) thin film with its two platinum electrodes. The piezoelectric layer allows simultaneous actuation and detection of the resonant frequency (and corresponding quality factor) of the membranes. First, MIP with template molecule 2,4-D and corresponding negative imprinted polymer (NIP) for control purpose were deposited on the membranes. The second step consisted in the polymerization of the MIP under UV light (365 nm) and nitrogen stream. For the first time to the authors’ knowledge, real time MIP polymerization has been monitored by following the membrane’s resonant frequency shift thus determining a minimum time for a complete polymerization and allowing the study of viscoelastic properties of the MIP during this phase. In our case, MIP was deposited on the clamped part of the membrane, allowing a much higher sensitivity for stiffness changes than for mass changes. The resonant frequency increase during polymerization traduced a higher rigidity of the MIP due to its progressive cross-linking on the membrane’s surface. Following to the polymerization, dip-and-dry experiments were performed in order to validate the MIP’s functionality. A first washing step of the template resulted in a high decrease of the resonant frequency and the quality factor traducing a decrease of MIP’s stiffness. This is mainly confirmed by the quality factor evolution as its decrease is relevant of the MIP softening. These results demonstrated the extraction of the template molecule 2,4-D. On the contrary, after incubation, frequency and quality factor levels were close to the initial ones showing that the MIP becomes a “rigid” film again as its pores are progressively occupied by the template molecules. Relevance of the obtained results was confirmed by the low frequency and Q-factor shifts obtained on the NIP control. Works are under progress on the precise determination of the sensor performances and the extension of the method to other MIP-template molecule couples.


11:30 AM V4.8
Poly (3-hexylthiophene)-ZnO Nanocomposites For Novel Organic -Inorganic Hybrid Sensor. Camilla Baratto¹, Guido Faglia¹, Giorgio Sberveglieri¹, Massood Z. Atashbar² and Erika Hrehorova²; ¹Chemistry and Physics, INFM-CNR & University of Brescia, Brescia, Italy; ²Electrical and Computer Engineering, Western Michigan University, Kalamazoo, Michigan.

Recently, organic-inorganic nanocomposites have been center of attention due to their potential for improvement of optical, electrical and mechanical properties of materials. Organic polymers have found growing interest due to their potentials for semiconductor electronics applications such as light-emitting diodes, thin-film transistor, photovoltaic, chemical and biological sensors. Moreover, the ease of their manufacturing process and low temperature processing would lead to lower cost of such devices. In this work we report the use of p-type conducting polymer Poly (3-hexylthiophene) (P3HT) mixed with nanosized Zn powder to obtain a thin film based conductometric sensor with enhanced selectivity and sensitivity. Regioregular P3HT dissolved in chloroform was mixed with ZnO nanopaarticles dissolved in chloroform to achieve 90:10, 70:30, 50:50, and 100:0 ratios of P3HT:ZnO (v/v). Solution was deposited on Al2O3 substrate with Pt contact and heater by drop casting and let to dry. FTIR analysis determined the presence of P3HT vibration peaks in all films as well as the presence of ZnO peaks where expected. Functional tests were carried out by a volt-amperometric technique at constant bias. All characterizations were performed by keeping the test chamber at 20°C with an atmospheric pressure and 50% relative humidity (RH). Sensors were tested in presence of NO2 (0.1-5 ppm), NH3 (500 ppm) and CO (500 ppm) and ethanol (500 ppm) diluted in humid air. We observed reversible current increase at low working temperature (50°C) towards NO2, with no interference form humidity CO and ethanol. A lower effect by NH3 was observed, namely a current decrease. Relative response to 1 ppm of NO2, defined as (Igas- Iair)/ Iair ×100, is 300%. The effect of introduction of ZnO nanoparticles into the polymeric matrix is to enhance the relative response as well as the recovery times towards NO2.


11:45 AM V4.9
Electrode Arrays of Carbon Nanofibers for Biosensing at Single Molecular and Cellular Levels Jessica Erin Koehne^1,2, Hua Chen³, Alan Cassell⁴, Barbara T. D. Nguyen¹, M. Meyyappan¹, Gang-yu Liu² and Jun Li¹; ¹NASA Ames Center for Nanotechnology, NASA Ames Research Center, Moffett Field, California; ²Chemistry, University of California, Davis, Davis, California; ³NASA Ames Center for Nanotechnology, ELORET Corporation, Moffett Field, California; ⁴NASA Ames Center for Nanotechnology, University of California, Santa Cruz, Moffett Field, California.

Carbon nanofibers (CNFs) are highly conductive and robust materials with high aspect ratios. Their unique properties and intriguing nanostructure can be employed to develop new tools to interrogate biomolecules and cells at nanoscale. Here, we report two studies using vertically aligned CNFs. First, a reliable nanoelectrode array (NEA) based on vertically aligned CNFs embedded in SiO2 is used for ultrasensitive DNA detection. Characteristic nanoelectrode behavior is observed using low-density CNF arrays for measuring both bulk and surface immobilized redox species such as K4Fe(CN)6 and ferrocene derivatives. The open-end of CNFs presents similar properties as graphite edge-plane electrodes with wide potential window, flexible chemical functionalities, and good biocompatibility. Oligonucleotide probes are selectively functionalized at the open ends of the nanofiber array and specifically hybridized with oligonucleotide targets. The guanine groups are employed as the signal moieties in the electrochemical measurements. Ru(bpy)32+ mediator is used to further amplify the guanine oxidation signal. The hybridization of subattomoles of PCR amplified DNA targets is detected electrochemically by combining the CNF nanoelectrode array with the Ru(bpy)32+ amplification mechanism. Second, the SiO2 matrix was etched back using a plasma process to produce needle-like protruding nanoelectrode arrays. This platform can be used towards biosensing at the single cell level by penetrating fibers into cells for investigating gene transfection, electrical stimulation and detection of cellular processes Extensive confocal microscopy measurements will be present to verify the viability of PC12 neural cells upon CNF impaling, as well as determining the location of the CNFs. Our goal is to take the advantage the nanostructure of CNF arrays for unconventional biomolecular studies requiring ultrahigh sensitivity, high-degree of miniaturization, and selective biofunctionalization.


SESSION V5: Biosensors and Hybrid Sensors II
Chairs: Elisabetta Comini and Vincenzo Guidi
Wednesday Afternoon, April 11, 2007
Room 2008 (Moscone West)
2:00 PM *V5.1
Plasmonics for Chemical and Biochemical Sensing: New Geometries, Spectroscopies, and Interfaces. Naomi Halas, Rice University, Houston, Texas.

By combining chemical fabrication methods with computational electromagnetic modeling, metallic and metallodielectric nanoparticle-based substrates of a variety of geometries can be designed and fabricated that support intense near fields at specifically desired wavelengths. In addition to large surface fields, designing nanostructures with new geometries that support large local fields on open surfaces, and matching the field volume at the substrate surface to the spatial extent of the analyte of interest, are critically important aspects of advanced sensor substrate design. This design-based approach allows for highly reliable and controlled surface enhanced Raman scattering (SERS) substrates, and can also be extended to other spectroscopies, such as surface enhanced infrared absorption (SEIRA) spanning other spectral regions. Multiple spectroscopies can also be combined on a single substrate, an important advance towards true “analytical chemistry lab-on-a-chip” substrates. We will describe our recent experiments in implementing a strategy for profiling the near field of a SERS substrate using molecular rulers, and recent progress in the development of functional, molecular layers that serve as “signal transduction interfaces” for binding analytes and sensing specific aspects of the local chemical environment.


2:30 PM V5.2
Virus Assay Using Antibody-Functionalized Peptide Nanotubes Robert I MacCuspie¹, Phillp R Krause² and Hiroshi Matsui¹; ¹Chemistry, City University of New York, Hunter College, New York, New York; ²Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland.

Robust trace-level detection of viruses is crucial to meet urgent needs in fighting the spread of disease or detecting bioterrorism events. Here, we introduce a method for rapid and highly sensitive detection of viruses utilizing fluorescent antibody nanotubes. When each virus (adenovirus, HSV-2, influenza B, and vaccinia) was mixed with antibody nanotubes in solution, we observed that these nanotubes rapidly aggregated around the viruses to form a networking structure. Light scattering also revealed that the size of the aggregates increased as the concentrations of viruses increased. Trace amounts of these viruses were detected on attomolar order by changes in fluorescence and light scattering intensities of the aggregated dye-loaded antibody nanotubes around viruses by flow cytometry, which was used to simultaneously detect the light scattering and the fluorescence and to separate signals from unbound nanotubes, which otherwise were sources of background interference. A typical limit of detection for this assay was determined to be on the order of 102 pfu/mL by creating standard curves between the integrated fluorescence intensities of the nanotube-virus aggregates and the added virus concentrations. These standard curves also allowed us to quantify viral concentrations based on their fluorescence intensities. The increased size of the nanotube-virus aggregates resulted in an increase of their fluorescence intensities, since more antibody nanotubes are contained in the larger aggregates, consistent with our observation of a linear correlation between the integrated fluorescence intensities of aggregates and the concentrations of viruses on a log scale. High specificity of anti-HSV-2 nanotube toward the targeted virus was also demonstrated by quantifying the concentration of HSV-2 in mixed solutions of HSV-2 and SV-40. Typically, we obtained the fluorescence data through flow cytometry in under five minutes, and with standard curves previously prepared, the overall process takes only 30 minutes from receipt of the sample in the lab until the final quantitative data are ready. If the gating protocols for the fluorescence-FCS intensity distribution and standard curves between integrated fluorescence intensities of the nanotube-virus aggregates and virus concentrations are prepared for targeted viruses in advance, this nanotube assay can be rapidly applied to determine viral concentrations in unknown samples. This antibody nanotube assay could complement other existing viral assays such as PCR, which detects virus structures rather than nucleic acids, and this feature makes the antibody nanotube assay more versatile in the detection of a variety of viruses


2:45 PM V5.3
Nanospring -Based Biosensors for Electrical DNA Microarrays. David N McIlroy¹, James Nagler², Larry Branen³, Joshua Branen³, Giancarlo Corti¹, Lidong Wang¹ and M. Grant Norton⁴; ¹Physics, University of Idaho, Moscow, Idaho; ²Biological Sciences, University of Idaho, Moscow, Idaho; ³Food Science and Toxicology, University of Idaho, Moscow, Idaho; ⁴Mechanical and Materials Engineering, Washington State University, Pullman, Washington.

It is well known that nanomaterials have unique surface properties that make them attractive for biological sensing. Many of the current uses of nanomaterials in biosensing are photonic in nature, where the primary mode of sensing is via optical pumping. With the success of photonic based sensors there has been a move to develop electrical based biosensors with nanomaterials. The difficulty is the integration of nanoscale materials into an electrical device that is economic and scalable. We have developed a process that allows for the growth of nanosprings in predetermined patterns using standard lithographic techniques. This breakthrough has greatly simplified device fabrication. The sensors utilize mats of nanosprings as the sensing material and are grown across two or more electrodes. The nanosprings are formed from silica and can be coated with metal nanoparticles to increase their conductivity. Because of the unique surface stoichiometry of the silica nanosprings, the mats of bare nanosprings have conductivities in the picoamp range. The conductivity of the mats can be increased by coating them with metal nanoparticles. Upon exposure of the bare nanospring mats to a buffer solution the conductivity increases to the microamp range. Upon exposure to a buffer solution containing DNA the conductivity increases to the milliamp range. A detailed analysis of the I-V characteristics, transport properties and surface interactions of the nanospring-based biosensor will be presented.


3:30 PM V5.4
Hazardous Gas Sensors Based on Polyaniline Nanofibers Shabnam Virji, Jesse Fowler and Bruce H. Weiller; The Aerospace Corporation, El Segundo, California.

Polyaniline nanofibers are versatile sensor materials for detection of a variety of analytes including acids, bases, redox active agents, and organic vapors at room temperature. The nanofibers form stable dispersions in water and can be easily modified with inorganic and organic additives to create new composite materials that can enhance detection of analytes over unmodified nanofibers. We have shown that polyaniline nanofibers modified with copper chloride and related salts give a greatly enhanced response to hydrogen sulfide that is orders of magnitude greater than the unmodified nanofibers. Other inorganic additives can be used to create sensors for many other toxic analytes of interest. Organic additives can also be used to enhance the sensing ability of polyaniline nanofibers for high priority toxic gases relevant to homeland security. Recently, we have shown that doped, unmodified polyaniline nanofibers can detect hydrogen well below the explosion threshold of 4%. We have now demonstrated an entirely new response to hydrogen when platinum is used as the electrode material instead of gold. An overview of these results will be presented.


3:45 PM V5.5
Abstract Withdrawn


4:00 PM V5.6
Electrical Characterization of DNA Deposition and Hybridization using MOS Capacitors. Sebania Libertino, Manuela Fichera and Salvatore Lombardo; Catania, CNR - IMM, Catania, Italy.

The need to fabricate efficient biosensors exhibiting prompt data read-out and data elaboration are driving the research towards their integration with microelectronic devices. The use of CMOS compatible devices is considered a valid approach to efficiently combine the well established microelectronic technology with the increased need of molecular recognition, felt in our everyday life. In this work we fabricated Si-based MOS capacitors, the fundamental element in the fabrication of a CMOS devices, using as a dielectric a thin silicon dioxide layer, 15 nm thick. The SiO₂ was functionalized in order to anchor, using an optimized immobilization protocol, DNA strands and enzymes. The immobilization protocol consists of four steps: i. oxide activation, ii. silanization, iii. linker molecule (glutaraldheyde, GA) deposition, vi. DNA (or enzyme) immobilization. A particular attention was devoted to fully characterize each protocol step and to verify the compatibility with the VLSI processing. Both X-ray photoelectron spectroscopy and atomic force microscopy were used to this purpose. The electrical characterization was carried out using a phosphate buffer solution (PBS) 1M deposited as a drop on the sample surface. The solution pH was varied from 3 to 8. The linker molecule deposition has tremendous effects on the MOS capacitor flat band voltage (V_FB). In fact, a shift of about 1 V was observed when the electrical characteristics of the reference (only SiO₂) and the GA deposited samples were compared. Moreover, when high voltages are applied to the gate (5V) the GA tends to collapse on the SiO₂ layer causing a further shift in the VFB. It should be mentioned that GA is widely used as linker molecule for DNA, enzymes and protein deposition. If big molecules, e.g. the enzyme glucose oxidase from Aspergillus Niger, are bonded to the GA a stabilization of the MOS characteristics is observed. It is due to the immobilization of the GA linking the substrate to the enzyme. Finally, the DNA deposition causes a further shift in the V_FB, below 0.3 V. The pH effect was tested also on these samples and a model of the capacitor behavior is proposed. The presence of DNA strands suspended in the PBS drop has also been evaluated and the device behavior as a function of the time monitored. Hence, the kinetic of DNA hybridization was studied. Measurements of oxide aging will also be discussed.


4:15 PM V5.7
A Maximum Entropy-Nonlinear Least Squares Analysis on ds-DNA based Optical Molecular Rulers. Mani Prabha Singh¹ and Geoffrey F Strouse¹; ¹Chemistry and Biochemistry, Florida State University, Tallahassee, Florida; ²Chemistry and Biochemistry, Florida State University, Tallahassee, Florida.

The structural changes taking place in a biomolecule during specific binding events are measurable with optical molecular rulers. Fluorescence spectroscopy is an important tool in these studies. A steady state measurement gives an averaged value of the distance due to the flexibility of the rulers which arises due to the linkers attaching the fluorophore probes. As a result, a time resolved (tr)- spectroscopic measurement gives a broadened lifetime peak due to the presence of a distribution of distances. A maximum entropy method-nonlinear least squares (MEM-NLLS) fit to the time resolved data determines the broadening of the lifetimes observed due to this flexibility. This broadened peak is resolvable into its constituents and hence the presence of different states/conformers or a distribution of distances can be detected. A double strand (ds-) DNA based optical ruler involving energy transfer from a cyanine fluorophore, Cy5 to a 1.5nm Au nanoparticle (NP) is studied as a function of distance and orientation. The energy transfer efficiency follows a (1/R)4 dependence, where R is the distance separating the fluorophore Cy5 from the Au NP. Cyanine family of fluorophores, because of their structure, is known to closely interact with the ds-DNA structure. Steady-state as well as time-resolved fluorescence spectroscopy is carried out on the ds-DNA construct and a MEM-NLLS analysis was carried out on the time resolved data at various distances. The results confirm the broadening as well as the preference of certain sites by the dye.


4:30 PM V5.8
VOC Gas Sensing Properties of Organic/MoO3 Hybrid Thin Films with Various Polyaniline Derivatives. Ichiro Matsubara, Toshio Itoh, Woosuck Shin and Noriya Izu; National Institute of Advanced Industrial Research & Technology, Nagoya, Japan.

Alternately stacked organic-inorganic hybrids that consist of semiconductive molybdenum trioxide (MoO3) sheets (host) and various organic components (guest) can be used as volatile organic compound (VOC) sensing materials. Almost all the organic/MoO3 hybrid sensors show a distinct response to aldehydic gases, i.e., formaldehyde and acetaldehyde, whereas they show little or no response to other VOCs. The typical organic/MoO3 hybrids ever prepared, such as polypyrrole/MoO3 and polyaniline (PANI)/MoO3 hybrids, have a higher sensitivity to formaldehyde than to acetaldehyde. We have also reported that organic/MoO3 hybrids have a great potential for selective VOC sensing, because the sensing properties of organic/MoO3 hybrids can be controlled by modifying the interlayer organic components, which have the function of molecular recognition. Therefore, it is expected that organic/MoO3 hybrids with a new type of organic components could show a higher sensitivity to acetaldehyde than to formaldehyde. In this study, we have investigated the VOC-sensing properties of organic/MoO3 hybrid thin films with various PANI-derivatives. As results, several PANI-derivatives/MoO3 hybrid thin films a higher sensitivity to acetaldehyde than to formaldehyde. We will report the details of preparation and VOCs (specifically aldehydic gases) sensing properties of PANI-derivatives/MoO3 hybrid thin films. This work was partially supported by New Energy and Industrial Technology Development Organization (NEDO), Japan.


SESSION V6: Biosensors and Hybrid Sensors III
Chairs: Vincenzo Guidi and Xiao-Dong Zhang
Thursday Morning, April 12, 2007
Room 2008 (Moscone West)
8:30 AM V6.1
Electrochemical Release of Immobilized IgG Protein. Tanveer Mahmud¹, Arnan Mitchell¹, Sally Gras², Adrian Trinchi³ and Kourosh Kalantar-zadeh¹; ¹Electrical and Computer Engineering, RMIT University, Melbourne, Victoria, Australia; ²Biomolecular of Chemical and Biomolecular Engineering, University of Melbourne, Melbourne, Victoria, Australia; ³CSIRO, Melbourne, Victoria, Australia.

In this paper, we present the controlled release of IgG protein molecules using a thiol-gold linkage. This process is based on the electrochemically programmed release of immobilized protein from gold coated surfaces. Fluorescence microscopy is used to image the release of fluorescently tagged IgGs in phosphate buffered saline. In this technique, the reductive desorption of self-assembled monolayers is employed for the release of proteins, which are immobilized on the surface either by non-colvalent or covalent interactions. The voltage applied for the release of proteins is in a range of -1.5V to -60V. Hydrophobic immobilzation of proteins on the surface is achieved by incubation of the protein solution for several hours on a substrate with a monolayer of self assembled thiols containing no carboxylic head groups. Covalent immobilization of proteins is achieved by incubating protein solutions with the same surfaces in the presence of N-hydroxysuccinimide (NHS). The carbodiimide functionality of the NHS groups activates the carboxylic functional groups on the thiol layer promoting the formation of esters. These esters then react with amine groups on the IgG protein covalently coupling the protein to the surface. In both cases, voltage induces protein release from the surface. The release of small molecules (e.g., drugs), biopolymers (e.g., peptides, proteins, DNA), and protein assemblies (e.g., viruses) can be controlled in a programmable manner using this technique. The method has a plethora of promising applications in the fabrication of controlled drug release devices, programmable DNA/protein arrays and micro-reactors.


8:45 AM V6.2
Manufacturable Carbon Nanotube Biosensor Chips for Protein and Cell Detection Fumiaki Ishikawa, Koungmin Ryu, Alexander Badmaev and Chongwu Zhou; USC, Los Angeles, California.

Significant effort has been devoted to the study of biosensing using individual single-walled carbon nanotube (SWNT) devices. Few reports exist, however, on manufacturable construction of such biosensing chips, which are crucial for the realization of disposable diagnostic tools. In this talk, we will present two manufacturable approaches for the construction of the biosensor chips using carbon nanotubes. The first approach is based on chemical vapor deposition (CVD) growth of SWNTs on entire wafers followed by metal electrode patterning using a shadow mask and removal of unwanted nanotubes using oxygen plasma. We were able to get about forty devices on one wafer with a narrow resistance distribution (about 20~300 killo-ohm), indicating the high reproducibility and manufacturability of our processes. The other approach is based on our recent success of growing massively aligned carbon nanotubes on a-plane sapphire and miscut quartz from patterned catalyst islands at desired locations. This approach has led to high-density biosensor arrays based on aligned nanotubes. In addition, we investigated the device performance for protein sensing and observed pronounced sensitivity from 10 nM down to 10 pM by metal cluster coating of the nanotubes. The possible mechanism for the improvement was investigated with a control experiment, and we suggest the formation of Schottky barrier between the carbon nanotube and metal cluster interface plays an important role in enhancing the sensitivity. Furthermore, we have applied such nanotube sensors to brown tide algae detection, which is responsible for harmful brown tide, and demonstrated sensitivity of 8*105 cells/ml with selectivity using the recently developed antibody for the algae cell.


9:00 AM V6.3
Abstract Withdrawn


9:15 AM V6.4
Functional Core-Shell Nanoparticles for Biochemical Sensors. Achim Weber¹, Kirsten Borchers¹, Herwig Brunner^1,2 and Gunter E. M. Tovar^1,2; ¹Biomimetic Surfaces, Fraunhofer-IGB, Stuttgart, Germany; ²University Stuttgart, IGVT, Stuttgart, Germany.

Investigations on a proteomic level have become feasible on the basis of extensive knowledge gained from genomic research. Chip-technology, though, while being a very successful tool for genomic work, can't be easily adopted for application in proteomics. Because of the complexity of protein-chemistry and a lack of high-quality capture-molecules, large-scale protein-profiling still has to be done by 2D-GE rather than by chip-based methods. However, when targeting at the detection of very low abundant proteins or at the detailed analysis of individual candidates and for diagnostic purposes, protein bio-chips are a very promising technology. In our approach to a flexible surface-chemistry for structured protein-immobilization we use nanoparticles as carriers for all different kinds of capture-molecules.[1] Nanoparticles display a very large surface, therefore we expect to generate highly sensitive micro-chip surfaces by adsorbing mono- or multilayers of functional nanoparticles onto a solid substrate. Affinity-nanoparticles applied in suspension have proven to be a very useful tool for protein-separation. We have shown that particle-bound proteins can be analysed by MALDI mass-spectrometry directly at the particles' surface as nanoparticles do not desturb the MALDI-process. Furthermore we have demonstrated that functional nanoparticles can be deposited on activated surfaces in a micro-structured way by combination of a broad range of top-down structuring methods.[2] We will now present results concerning the maintainance of protein function on nanoparticulate chip-surfaces, the sensitivity and the dynamic range of nanoparticle-chips and chip-readout by fluorescence-detection [3] and MALDI-mass-spectrometry.[4] [1] Schiestel T.; Brunner H.; Tovar G.E.M. J. Nanosci. Nanotechn. 2004, 4, 504. [2] Tovar, G. E. M.; Weber, A. Ency. Nanosci. Nanotechnol. 2004, 1, 277. [3] Borchers K.; Weber A.; Brunner H.; Tovar G.E.M. Anal. Bioanal. Chem. 2005, 383, 738. [4] Weber, A.; Borchers, K.; Schmucker, J.; Brunner, H.; Tovar G.E.M., Can. J. Anal. Sci. Spectros. 2005, 50, 49.


9:30 AM V6.5
Biological Sensing Using Surface Potential Force Microscopy Asher K Sinensky¹ and Angela M Belcher^1,2; ¹Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts; ²Bioengineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.

Many biological molecules have a native state which includes the presence of charge centers (e.g. the negatively charged backbone of DNA). Because of this inherent charge, the formation of highly specific complexes between biomolecules will often be accompanied by local changes in charge density. Here we demonstrate a sensor for charged biomolecules, including proteins and DNA, using the scanning probe technique known as Surface Potential Force Microscopy (SPFM or Kelvin Probe). If a probe molecule is patterned onto a surface, biological interactions can result in the highly specific binding of a target biomolecule which may in turn result in a variation in the local surface potential due to a change in local charge density. By spatially resolving this variation in surface potential it is possible to measure the presence of a specific bound target biomolecule on a surface without the aid of special chemistries or any form of labeling (fluorescent or otherwise). This work could provide a framework for future biosensors or microarrays with feature densities hundreds of times greater than current microarray technologies.


9:45 AM V6.6
Surface Modification and Functionalization of Silicon Carbonitride for Resonant NEMS Biosensing Applications Lee M. Fischer^1,2, Wally Qiu³, Ni Yang³, Mark T. McDermott^3,2 and Stephane Evoy^1,2; ¹Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada; ²Nanodevices and Sensors, National Institute for Nanotechnology, Edmonton, Alberta, Canada; ³Chemistry, University of Alberta, Edmonton, Alberta, Canada.

Identification and quantitative analysis of biological molecules is vital in disease detection, drug discovery, and many fundamental problems in molecular biology. Cantilever devices have been proposed as highly-sensitive transducers for the assaying of such biomolecular systems. Surface machining now routinely allows the fabrication of mechanical objects with lateral dimensions reaching the sub 100 nm range and resonant frequencies operating in the GHz range. Such nanoelectromechanical systems (NEMS) are of great interest for the detection and assaying of biomolecules with high sensitivity. The selective immobilization of molecular species onto device surfaces is however key to the successful development of any given biosensing platform. The functionalization of silicon has traditionally involved complex silane-based surface chemistries that offer limited reliability and stability. Alternatively, the coating of surfaces with a gold layer followed by the self-assembly of an alkane-thiol monolayer has also been employed to produce stable amine groups and facilitate further binding chemistries. Such steps however introduce additional fabrication complexities and can induce degradation of the mechanical properties of the NEMS resonator. Alternatively, we have recently established that PECVD silicon carbonitride (SiCN) directly hosts stable amine groups without the need for complex attachment chemistries. Our previous work involving the fabrication and assaying of beam resonators in this material has also determined that it was on par with silicon for NEMS applications while offering the additional advantage of the tunability of its chemical and mechanical properties.[1] We here report the use of ammonia and oxygen plasmas to modify the SiCN surface for the eventual immobilization of carcinoembryonic antigen (CEA) onto resonating NEMS sensors. Similar methods have been used to aminate polymers[2] as well as carbon nanofibres[3] for biological and gas sensing, respectively. We characterize this modified surface chemistry using FT-IR and XPS, and correlate the resulting surface composition to plasma parameters (such as time, power, pressure). Fluorescently-tagged streptavidin, as well as succinimide and silane-based chemistries are used to quantify the resulting extent of the surface modification. Finally, we examine the resonant behavior of SiCN beams and cantilevers before and after a vapor-phase deposition of succinimide and silane-based monolayers onto their surfaces. [1] L.M. Fischer, et al. Mater. Res. Soc. Symp. Proc. Vol. 924 (2006) 0924-Z08-12. [2] H.-C. Wen, et al. Surface & Coatings Technol. 200, 3166-3169 (2006) [3] K. Nakanishi, et al. Analytical Chemistry 68, 1695-1700 (1996)


10:30 AM V6.7
Interferometric UV Lithography for Nanoscale Patterning of Biological Substrates Aschalew Kassu, Jean-Michel Taguenang and Anup Sharma; Physics, Alabama A&M University, Normal, Alabama.

Interferometric UV lithography with low-power 244 nm laser is used to produce micron and nano-scale periodic structures like gratings and microarrays in substrates of biological interest like phospholipid thin films as well as polymers like poly-L-Lysine and polybutadiene. Phospholipid films have found extensive uses as simple models of cell membranes. Model biomembranes are known to be excellent platforms for immobilizing antibodies for biosensing-related applications. Additionally, poly-L-lysine is an amino-acid polymer. Due to its hydrophilicity it is commonly used as a coating agent to promote cell adhesion in culture as well as for immobilization of oligonucleotides in DNA microarrays. Likewise, polybutadiene is a biologically benign polymer which holds promise as a substrate for sensing applications. The experiments described here were motivated by the promise of interferometric techniques to extend photolithography to produce nanometer scale features. Holographic gratings and microarrays are recorded in azo-dye (NBD)-labeled phospholipid thin films using 244 nm UV light. Diffraction efficiency of these gratings shows extreme sensitivity to humidity and can increase reversibly by two orders of magnitude in air, which is saturated with water vapor. This effect is related to the unique characteristics of phospholipid molecules to undergo hydration-dependent structural reorganizations and self-assembly. Lithographic patterning is explained as due to (i) laser-light induced gradient force and (ii) UV-induced photodissociation of phospholipid molecules. UV laser is seen to enhance hydrophilicity of polymer-substrates like poly-L-Lysine and poly-butadiene. Using phase-contrast microscopy, it is observed that UV-patterned hydrophilic arrays in poly-L-Lysine adsorb ambient humidity from air for several hours with relative humidity as low as 50%. Kinetics of this effect was investigated with a novel technique involving spatially periodic adsorption of ambient humidity by a holographically fabricated grating on film surface. Deep-UV is routinely used for crosslinking biological molecules on poly-L-Lysine. These results will be important in controlling the ambient conditions used for crosslinking. In thin-films of polybutadiene, interferometric UV patterning results in nanowells which are 30 nm deep and have an array spot-size of 500 nm x 500 nm. The technique provides a new platform for immobilizing biological molecules for high-density sensor chips. This work is supported by a National Science Foundation EPSCoR Grant.


10:45 AM V6.8
The Fabrication and Performance of A Magnetoelastic Material as a Platform for Liquid Based Biosensors Bryan A Chin, Michael L Johnson and Rajeesh Guntapali; materials engineering, auburn university, Auburn, Alabama.

Every year over 76 million Americans become ill due to the presence of food-borne pathogens in food products. These illnesses, hospitalizations and lost productivity are estimated to cost over $30 billion annually. Many of these food-borne illnesses could be avoided if better methods of rapid detection of pathogenic bacteria, spores and toxins in liquid samples of food were available. This paper presents the results of an investigation into the fabrication and performance of magnetoelastic particles as the basis for a biosensor for the detection of Salmonella typhimurium. Magnetoelastic material sensor platforms ranging in size from 5 x 10 x 100 microns to 10 x 50 x 500 microns were fabricated using sputtering and a microelectronics fabrication liftoff process. The composition of the amorphous magnetoelastic materials that were deposited in this experiment was Fe80B20. A detailed description and discussion of how the sputtering/deposition process was evolved to produce magnetoelastic platforms with good resonating parameters is presented. Bio-molecular recognition receptors specific to Salmonella typhimuirium bacteria were then chemically bound to the specially prepared surfaces of the magnetoelastic materials platforms to form a biosensor. The bio-molecular recognition receptors serve to capture and bind the target pathogens/toxins and determine the specificity of the sensor. Each biosensor as fabricated has a characteristic resonance that is dictated by the particle’s dimensions and mass. A change in the resonance characteristics of the magnetoelastic particles results when binding of the target species (in this case Salmonella typhimuirium) to the magnetoelastic particles occurs. The magnetoelastic biosensors are remotely and wirelessly driven into resonance using an external magnetic field and changes in resonance characteristics of the magnetoelastic materials are monitored remotely and wirelessly to identify binding of the target bacteria/viruses/toxins. The wireless and remote characteristics of the magnetoelastic biosensors make them ideal for use in liquefied food samples. Results of carefully controlled mass loading experiments of the magnetoelastic platforms are presented that show the sensor platforms have detection sensititivities in liquids that should allow the detection of as few as 100 cells of a target agent. Problems encountered during the fabrication and preparation of the biosensors for use in liquid food sample evaluations are discussed. The liquids used in food sample evaluation are typically buffered salt solutions that present an aggressive corrosive environment for the iron based biosensors. Deposition and heat treatment of Cr and Au interlayers as a barrier to corrosion were investigated. Finally the performance of the magnetoelastic biosensor in the detection of Salmonella typhimurium in a variety of liquids such as milk and juices is presented.


11:00 AM V6.9
Conductimetric Detection of Protein and Cancer Cells with Oxide Nanosensors on a SOP Platform. P Markondeya Raj, Janagama Goud, Jin Liu, Mahdevan Iyer, Zhong Lin Wang and Rao Tummala; Electrical and Computer Engineering, Georgia Tech. - Packaging Research Center, Georgia Institute of Technology, Georgia.

The emergence of digital convergence combining computing, communication, consumer functions in a single portable system, when coupled with the advances in medicine lead to a new class of sophisticated implantable bioelectronic systems that can sense, digitize, diagnose, monitor and even dispense medicine to the regions of the body that needs it. Large scale integration of multiplexed, ultra sensitive sensor arrays is critical for several applications such as early detection of diseases and real-time health diagnosis. Nanotechnology based sensor devices fabricated when biofuctionalized with the corresponding biomolecules lead to the next-generation embedded bio-sensor systems for early disease detection. Current ultrasensitive nanoscale sensor integration research is mostly confined to silicon platform with limited choice of sensing materials. Integrating sensors a organic systems packaging platform (System-On-Package) can easily couple the sensing with wireless and digital functions leading to highly integrated bioelectronic systems at low-cost. Semiconducting oxides are widely known and commercially applied for their gas sensing properties. However, biochemical sensing has mostly depended on optical and electrochemical techniques that are more cumbersome. This work investigates the biosensing characteristics of ZnO nanobelts, ZnO and doped barium titanate thin films. Nano zinc oxide sensors showed significant changes in conductivity after protein functionalization with rabbit IgG and hybridization with anti-rabbit IgG. Systematic changes in conductivity of nanosensors were also measured after coating the oxides with MCF-7 cancer cells and its antibodies. In another set of experiments, ZnO nanobelts showed systematic conductivity changes after functionalizing with S-100 Schwann nerve cells. The conductivity changes from rabbit IgG protein hybridization can be detected even with doped barium titanate films. The experimental results in this paper indicate that the conductimetric properties of nano and thin film oxides can be sensitized to protein and cancer cell hybridization reactions and can be accurately detected. This technique can also be applied to certain pathogen proteins or toxic proteins from the environment. These nanostructured oxide biosensors have potential for early detection of prostate-specific antigen (PSA) and breast cancer genes such as HER2 (or HER2/neu), BRCA1 and BRCA2 I. When combined with organic substrate packaging, integration of wireless and mixed signal interfaces, and microfluidic guidance of biological fluids, this SOP based system integration approach is expected to provide low-cost, real-time sensing for clinical diagnostics and early detection of cancer diseases.


11:15 AM V6.10
High Sensitivity Photonic Crystal Biosensor Incorporating Nanorod Structures for Enhanced Surface Area. Wei Zhang¹, Nikhil Ganesh¹, Ian D. Block² and Brian T. Cunningham²; ¹Department of Materials Science and Engineering, University of Illinois at Urbana Champaign, Urbana, Illinois; ²Department of Electrical and Computer Engineering, University of Illinois at Urbana Champaign, Urbana, Illinois.

Label-free optical biosensors have emerged as important tools for pharmaceutical research, diagnostic testing, and environmental monitoring. Development of sensor designs that enhance sensitivity is especially important because it allows detection of lower concentrations of analytes and detection of small molecules with a higher signal-to-noise ratio. Recently, optical biosensors based on photonic crystals have been demonstrated as a means for obtaining mass density sensitivity resolution < 0.1 pg/mm2. The sensor consists of a one-dimensional grating structure with a period of 550nm. Such structure is designed to reflect only a narrow band of wavelengths when illuminated with white light at normal incidence, where positive shifts of the reflected peak wavelength value indicate the adsorption of detected material on the sensor surface. In this work, we show that the surface area of such sensor is greatly enhanced through the incorporation of a porous titanium dioxide film into the device structure. The film is deposited by the glancing angle deposition technique in an e-beam evaporation system. By orientating the incoming flux at an oblique angle from the substrate normal, and under conditions of sufficiently limited adatom mobility, the self-shadowing effect during the deposition results in a porous film with a structure composed of isolated vertical nanorods with a rod diameter of 30nm and rod-rod spacing of 20nm. It is estimated that such a film of 60nm thick can provide a surface area enhancement of 4x compared to a flat surface. The high porosity of the film permits biomolecules to penetrate while the feature sizes of the nanostructure is still far below the resonant wavelength of the photonic crystal, minimizing scattering and absorption. The sensitivity of high surface area sensors is compared with sensors without the high surface area coating for detecting polymer film (amine polymer) adsorption, large protein (streptavidin) adsorption and detection of a small molecule (biotin). The enhancement factor is 4.2 for attachment of the amine polymer film that can conform to the available exposed surface area in a single monolayer and the enhancement factor reduces to 2.1 for the covalent attachment of streptavidin, indicating that the surface structure was penetrated more easily by the polymer molecules than by a large protein with a globular structure.


11:30 AM V6.11
Quantum Dot-molecule Energy Transfer Systems Applicable to Multiphoton-excited Imaging and Quantification of Biochemical Parameters in vivo. Andrew B Greytak, Rebecca C Somers, Emily J McLaurin, Moungi G Bawendi and Daniel G Nocera; Massachusetts Institute of Technology, Cambridge, Massachusetts.

Permanently tethered FRET couples comprised of a quantum dot (QD) donor and molecular chemosensor acceptor have recently been demonstrated as a route to dual-emission wavelength-ratiometric chemical sensors. The large multiphoton action cross-section characteristic of quantum dots suggests an important application for such sensors as bright sensing probes in the imaging of biochemical parameters in living tissues, for example in metabolic profiling of murine tumor models via intravital multiphoton laser-scanning microscopy (MPLSM). The talk will describe design considerations for bioavailable and robust nanosensors, including the establishment of QD surface chemistry and linking chemistry to create a modular scaffold for nanosensor development, and will additionally discuss sensor operation under two-photon excitation and in biological contexts, with QD nanosensor probes for pH serving as a biomedically relevant example.


11:45 AM V6.12
Conjugated Polyelectrolytes as Tools for Decorating Biomolecules in vitro, in tissue and in vivo Olle Inganas¹, Peter Nilsson¹, Anna Herland¹, Per Bjork¹, Per Konradsson³, Per Hammarstrom², Jon Jonasson⁴, Mikael Lindgren⁵, Andreas Aslund³ and Gunilla Westermark⁶; ¹IFM, Linköping University, Biomolecular and organic electronics, Linkoping, Sweden; ²IFM, Linköping University, Biochemistry, Linkoping, Sweden; ³IFM, Linköping University, Organic chemistry, Linkoping, Sweden; ⁴Biomedicine and Surgery, Linköping University, Clinical Chemistry, Linkoping, Sweden; ⁵Physics, The Norwegian University of Science and Technology, Trondheim, Norway; ⁶Biomedicine and Surgery, Linköping University, Cell Biology, Linköping, Sweden.

Photoluminescence from conjugated polymers in the form of charged macromolecules, polyelectrolytes, is a tool to image the presence and activity of biological macromolecules in simple and in complex systems. The CPEs form complexes with biological macromolecules, by means of all the weak interactions available from biological interactions….van der Waals interactions, electrostatic and dipolar interactions, hydrophobic and hydrogen bonding. The geometry of the polymeric emitter is influenced by the interactions with target molecules, and the emission and absorption properties change due to these changes. By this means biomolecular events such as conformational changes, hybridisation of DNA chains and antibody-antigene reactions may be followed. Such studies can be done in buffers, in tissue samples when appropriately treated, and in in vivo studies. Protein aggregation resulting in amyloid fibrils can be followed both in vitro and after deposition in tissue; the target amyloids are selectively decorated in tissue samples. By this means amyloid plaque implicated in Alzheimer disease can be decorated. Such decorated deposits are also accessible in multiphoton excitation, where stimulus in the near infrared leads to red emission by two photon processes. Two photon processes are enhanced in the CPEs studied, and therefore offers interesting options for imaging of live cells and tissue.


SESSION V7: Biosensors and Hybrid Sensors IV
Chairs: Elisabetta Comini and Xiao-Dong Zhang
Thursday Afternoon, April 12, 2007
Room 2008 (Moscone West)
2:00 PM V7.1
Nanoplasmonic Molecular Ruler for Studying DNA-protein Interactions and Proteomic Changes. Fanqing Chen¹, Gang L. Liu² and Luke Lee²; ¹Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California; ²University of California at Berkeley, Berkeley, California.

Protein-nucleic acid interactions are essential to genetic information processing. The detection of size changes in nucleic acids is the key to mapping such interactions, and usually requires oligonucleotide substrates with fluorescent, electrochemical or radioactive labels. Recently, methods have been developed to tether DNA to highly water-soluble Au nanoparticles. Single gold and silver nanoparticle dimer has been demonstrated for distance measurement9. We present here a nanoplasmonic molecular ruler consisting of Au-DNA nanoconjugates. The scattering spectra of individual Au-DNA nanoconjugates showed red-shifted peak plasmon resonance wavelength dependent on DNA length, which can be measured with sub-nanometer axial resolution, averaging ~1.24 nm peak wavelength shift per DNA base pair (bp). The ruler allows label-free, quantitative, and real-time measurement of nuclease activity. The ruler was further developed into a new DNA footprinting platform, which can accurately detect and map the specific binding of a protein to DNA. This work promises a fast and convenient platform for mapping DNA-protein interactions, nuclease activity monitoring, and other DNA size-based applications. (published in Nature Nanotechnology 1, 47-52). In addition to measurement of protein DNA interaction, we have also constructed the ruler for use in measurement of posttranslational changes catalyzed by proteases and protein kinases, at sensitivity level comparable to radioactive labeling methods.


2:15 PM V7.2
Vacuum Deposited Porphyrine/Phthalocyanine Films as Promising Optical Gas Sensing Materials Gianluigi Maggioni¹, Michele Tonezzer^2,3, Sara Carturan¹, Alberto Quaranta³, Katerina Severova^4,2 and Gianantonio Della Mea^3,2; ¹INFN-LNL, Università di Padova c/o, Legnaro, Italy; ²Laboratori Nazionali di Legnaro, Istituto Nazionale di Fisica Nucleare, Legnaro (PD), Italy; ³DIMTI, Università di Trento, Povo (TN), Italy; ⁴Institute of Physical and Applied Chemistry, Brno University of Technology, Brno, Czech Republic.

Porphyrins and phthalocyanines are macrocyclic compounds which have been arousing increasing attention in the last decade due to their peculiar electrical and optical properties. Particularly interesting are the optical properties of these macrocycles, such as the intense absorption of visible light and the chemical stability upon illumination, which can be tailored by modifying their basic molecular structure. These properties have been used for developing optical chemical sensors, since the interaction between the analyte and the macrocycle gives rise to measurable changes of the light absorption of the macrocycle. In order to be exploited as sensing materials, porphyrins and phthalocyanines must be usually deposited as solid films onto a suitable substrate. A large number of chemical techniques (spin coating, Langmuir-Blodgett, etc.) has been used and studied for this purpose. Fewer efforts, on the contrary, have been made to produce thin films by means of vacuum deposition techniques in spite of the fact that these techniques assure several advantages with respect to the standard chemical methods such as great reproducibility, uniformity and stricter control of the film thickness. Moreover, the vacuum deposition techniques produce thin films without using any extraneous compound such as organic solvents, thus allowing to obtain samples with very high purity. Sample purity is expected to play an important role in the chemical sensing field, because the presence of retained solvent in the film can partially hinder the film/analyte interaction, thus lowering the optical response to the analyte. In this work two vacuum deposition techniques were used for the production of thin films of macrocyclic molecules: high vacuum evaporation (VE) and glow-discharge-induced sublimation (GDS). Vacuum evaporation is a well known deposition method; while it has been already widely used for the production of phthalocyanine films, vacuum evaporation of porphyrin films is still relatively little explored. GDS technique, on the contrary, has been used very little for the deposition of both phthalocyanines and porphyrins: it is based on the use of a radio frequency plasma, which gives rise to the sublimation of the macrocyclic molecules and to their condensation onto the substrate. Two macrocycles were selected for this work: 5,10,15,20 meso-tetraphenyl porphyrin (H2TPP) and copper phthalocyanine (CuPc). H2TPP and CuPc films were deposited by VE and GDS techniques. H2TPP films were also deposited by spin coating (SPIN), by exploiting the solubility of this compound in organic solvents. In order to evaluate the sensing properties of H2TPP and CuPc films, their optical response to volatile organic compounds (VOCs) was tested at room temperature, by exposing the sample to VOC vapours at different concentrations. All the vacuum deposited films exhibited short response times and much higher sensitivity than those deposited by standard chemical methods.


2:30 PM V7.3
Preparation of Layered Organic/Molybdenum Trioxide Hybrid Thin Films as High Sensitive VOC Sensors. Toshio Itoh, Ichiro Matsubara, Woosuck Shin and Noriya Izu; Advanced Manufacturing Researci Institute, National Institute of Advanced Industrial Science and Technology (AIST), Nagoya, Aichi, Japan.

The sick house syndrome is caused by several harmful volatile organic compounds (VOCs), specifically formaldehyde. The indoor regulation values of aldehydic gases concentration are indicated by the Ministry of Health, Labour and Welfare in Japan. To prevent this problem, using ventilation systems controlled by VOC sensors is one of the best approaches, because of not only the ventilation of indoor air but also energy saving. Therefore, VOC sensing devices which possess continuous monitoring and low-concentrate, i.e. sub-ppm level, VOC detection are required. Layered organic-inorganic hybrids of semiconductive molybdenum trioxide (MoO3) thin films with organic components, e.g. polyaniline (PANI) and poly(o-anisidine) (PoANIS), are investigated for the volatile organic compounds (VOCs) sensing properties by means of monitoring their electrical resistance. We tried new procedure of synthesizing organic/MoO3 hybrid thin film: 1) deposition of MoO3 thin films on a silicon substrate with a LaAlO3 buffer layer and a gold comb-type electrode by chemical vapor deposition (CVD); 2) insertion of sodium ions into MoO3 interlayers by reduction; 3) intercalation of organic components into MoO3 interlayers by ion exchange. MoO3 thin films were prepared by the pyrolysis of molybdenum hexacarbonyl in oxygen atmosphere by CVD. The MoO3 thin films were soaked into sodium hydrosulfite aqueous solution to reduce the MoO3 and to insert ion-exchangeable sodium ions between the MoO3 sheets. Thus-obtained films ([Na(H2O)2]xMoO3) then underwent an ion-exchange reaction. The [Na(H2O)2]xMoO3 films were soaked in organic polymers aqueous solutions to ion-exchange Na+ for organic polymers, respectively. The resulting hybrid films were washed quickly with distilled water and then dried. The VOC-sensing properties of the organic/MoO3 hybrid were determined experimentally using a flow apparatus. The organic/MoO3 hybrid thin film was placed in homeothermic chamber, and the resistance of the thin film was measured directly through the gold comb-type electrode. The target VOC concentrations were precisely controlled using the flow system with a mass flow controller. After the pure carrier gas was passed through the chamber, the target VOC flowed, and then the gas flowing into the chamber was again changed to pure carrier gas. The new-prepared organic/MoO3 hybrids show a distinct increasing resistive response to aldehydic gases. In contrast, there is little or no response to chloroform, alcohols, acetone, and aromatics. Moreover, these hybrids can detect sub-ppm concentration of VOCs. In this presentation, preparation of layered organic/MoO3 hybrid thin films as high-sensitive VOC sensors and its sensing properties will be reported. This work was partially supported by New Energy and Industrial Technology Development Organization (NEDO), Japan.


2:45 PM V7.4
Chiral Recognition with Enhanced Sensing Organic Thin-film Transistors. Luisa Torsi^1,2, Gianluca Maria Farinola¹, Patrizia Iliade¹, Maria Cristina Tanese^1,2, Francesco Marinelli¹, Mirizio Francesca¹, Omar Hassan Omar³, Ludovico Valli⁴, Gabriele Giancane⁴, Francesco Babudri^1,3, Francesco Palmisano¹, Pier Giorgio Zambonin^1,2 and Francesco Naso^1,3; ¹Chemistry, Università degli Studi di Bari, Bari, Italy; ²CE TIRES - Università degli Studi di Bari, Bari, Italy; ³Chemistry - CNR ICCOM, Università degli Studi di Bari, Bari, Italy; ⁴Innovation Engeneering, Università degli Studi di Lecce, Lecce, Italy.

Electronic detection with organic thin-film transistor (OTFT) sensors results in field-effect amplified responses repeatable within a standard deviation of few percentages [1]. Polycrystalline conducting polymers (CP) act both as transistor channel materials and sensitive layers and the CP side groups confer broad chemical selectivity but specificity and high sensitivity are yet open issues. Chiral discrimination is one of the hardest bench-test to prove sensors performance particularly in terms of selectivity and sensitivity. Here a OTFT gas sensor, bearing an amino-acid substituted CP active layer, is demonstrated to exhibit amplified sensitivity that allow to selectively detect β-citronellol enantiomers in the tens part per million (ppm) concentration range with highly repeatable responses. Markedly different sensitivities are seen for (S)-β-citronellol and (R)-β-citronellol and even for a racemic misture. The semi-conducting oligomers, which are designed to combine field-effect and enantiomeric recognition properties, are implemented in a novel sensing OTFT structure. Alkoxyphenylene-thienylene conjugated systems have been chosen for the active layer as they allow to covalently attach a wide variety of molecules as side groups, including bio-receptors [2-3], exhibiting also field-effect properties when deposited by the Langmuir-Schäfer (LS) procedure [4]. Chiral CP were synthesized already twenty years ago and differential detection of single enantiomers was performed with electrochemical, gravimetric and chemiresistor [5,6] sensors at part per thousand (ppth) concentrations. Our results demonstrate that combining field-effect amplified detection with chiral CP recognition properties allows enantiomeric discrimination at much lower concentration. This is a significant step further in the development of a highly-performing nanoscalable electronic sensing platform fully compatible with fast advancing organic electronic technologies. [1] Torsi, L. and Dodabalapur, A. Anal. Chem. 70, 381A (2005). [2] Babudri, F., Farinola, G.M., Naso, F. J. Mater. Chem. 14, 11 (2004). [3] Naso, F., Babudri, F., Colangliuli, D., Farinola, G.M., Quaranta, F., Rella, R., Tafuro, R., Valli, L. J. Am. Chem. Soc. 125, 9055 (2003). [4] Tanese, M.C., Farinola, G.M., Pignataro, B., Valli, L., Giotta, L., Conoci, S., Lang, P., Colangiuli, D., Babudri, F., Naso, F., Sabbatini, L., Zambonin, P.G., Torsi, L, Chem. Mat. 18, 778 ( 2006). [5] Severin, E. J., Sanner, R. D., Doleman, B.J., Lewis, N.S. Anal. Chem. 70, 1440 (1998). [6] de Lacy Costello, B.P.J., Ratcliffe, N.M., Sivanand, P.S. Synth. Met. 139, 43 (2003).


3:30 PM V7.5
PNA Based SERS Substrates for DNA Detection. Laura Fabris, Gary Braun, SeungJoon Lee, Mark Dante, Norbert Reich, Moskovits Martin, Thuc-Quyen Nguyen and Guillermo C. Bazan; Department of Chemistry and Biochemistry, University of California, Santa Barbara, California.

There is a need for developing methods that don’t require chemical modification of the target DNA and can detect the hybridization event with high specificity and sensitivity.[3, 4] In response, we have designed and tested ssDNA sensors based on the concept of Surface Enhanced Raman Spectroscopy (SERS). The assay contains a surface modified with single stranded PNA (Peptide Nucleic Acid) instead of ssDNA.[5, 6] ssPNA binds to complementary ssDNA more tightly and with better selectivity, relative to ssDNA. Moreover, PNA/DNA hybrids are less sensitive to ionic strength and pH. In this context we have taken advantage of the fact that before hybridization the ssPNA modified surface is neutral, whereas after binding to the complementary ssDNA the charge becomes overall negative. This allows to electrostatically bind positively charged nanoparticles (NPs) and to create SERS active hot spots directly on the hybridized structures, circumventing the need for covalent bonding.[7-9] The addition of a dye with absorption maximum in resonance with the laser wavelength (in our case Rhodamine 6G) and subsequent SERS analysis provide the Raman fingerprint of the dye as proof of the hybridization event. The assay involves commercially available materials and instrumentation. [1] D. Graham, R. Brown, W. E. Smith, Chem. Commun. 2001, 1002. [2] O. Brandt, J. Feldner, A. Stephan, M. Schröder, M. Schnölzer, H. F. Arlinghaus, J. D. Hoheisel, A. Jacob, Nucleic Acids Res. 2003, 31, [3] T. Endo, K. Kerman, N. Nagatani, Y. Takamura, E. Tamia, Anal. Chem. 2005, 77, 6976. [4] O. Brandt, J. D. Hoheisel, Trends in Biotechnology 2004, 22, 617. [5] a. J. Wang, Biosens. Bioelectron. 1998, 13, 757-762. b. J. Wang, Nucleic Acids Res. 2000, 28, 3011. [6] J. Wang, E. Palecek, P. E. Nielsen, G.. Rivas, X. Cai, H. Shiraishi, N. Dontha, D. Luo, P. A. M. Farias, J. Am. Chem. Soc. 1996, 118, 7667. [7] Y. Sun, W. Fan, M. P. McCann, V. Golovlev, Anal. Biochem. 2005, 345, 312. [8] A. Gourishankar, S. Shukla, R. Pasricha, M. Sastry, K.N. Ganesh, Current Applied Physics 2005, 102. [9] G.. Wang, R. W. Murray, Nano Lett. 2004, 4, 95.


3:45 PM V7.6
A Novel Glucose Sensor Based on the Deflection of a Thin Hydrogel Membrane Sandeep Mariserla¹ and Thomas J Mackin²; ¹Materials Science and Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois; ²Mechanical Engineering, California State Polytechnic University, San Louis Obispo, California.

Self-monitoring of blood glucose has become an important and critical tool for effective management of patients with diabetes. We describe here a novel MEMS sensor that can continuously measure, in real time, the concentration of glucose in a solution. The device utilizes a glucose-sensitive hydrogel membrane, which swells reversibly in the presence of a glucose containing solution. The amount of swelling is related to the concentration of glucose. The hydrogel is composed of 2-hydroxyethyl methacrylate (HEMA) functionalized with 3-acrylamidophenylboronic acid (AAPBA) groups as the glucose-sensitive moiety. Phenylboronic acid (PBA) derivatives interact with glucose by forming a charged complex, causing the hydrogel to swell by solvent intake. A thin hydrogel layer is processed into a laminated membrane architecture that includes one half of a parallel plate capacitor. The resultant swelling of the hydrogel deflects the membrane and moves that capacitor plate. Signal transduction arises directly from motion of the plate with respect to a fixed conducting pad, resulting in a change in capacitance. Hence the presence or variation in the concentration of glucose can be observed as a change in capacitance of the device. The device is fabricated using standard microfabrication techniques. A Single-Crystal-Silicon (SCS) wafer is fabricated into a die; this die is then placed into a tetramethyl ammonium hydroxide (TMAH) bath for anisotropic etching of the SCS. This step thins the wafer where the polymer membrane will reside, reducing etch time in subsequent steps. Si islands are patterned from the bottom side of the die using PR, followed by coating the top surface with an intermediate polydimethylsiloxane (PDMS) layer. This PDMS layer is the structural layer of the membrane, and also serves as a hermetic seal between the glucose solution and the capacitance gage. The glucose-sensitive hydrogel monomer is then flown onto the PDMS membrane in the final step and UV-polymerized, thus excluding and protecting it from the harsh processing conditions mentioned in the earlier steps. Results detailing the swelling properties of the AAPBA-containing HEMA hydrogel samples, their adhesion to the PDMS protective membrane and the deflection caused by their bi-layer expansion will be discussed. The mechanical properties of the bi-material membrane and it’s response to varying concentrations of glucose solutions will be analyzed. Determination of the bending mechanics of the glucose-sensitive bi-layer hydrogel membrane will help formulate the dimensions and the recipe for incorporation into the device.


4:00 PM V7.7
Highly Sensitive Nitric Oxide Biosensor: Detection Using X-ray Photoelectron Spectroscopy. Manish Dubey, Steven L. Bernasek and Jeffrey Schwartz; Department of Chemistry, Princeton University, Princeton, New Jersey.

Detection of gaseous nitric oxide (NO) in biological systems has attracted a lot of attention ever since its identification as the endothelial-derived relaxing factor (EDRF)1. NO also acts as a signal molecule in the nervous system, and is associated with the presence of infection and Alzheimer’s and other diseases. Apart from biological systems, NO is a main product released on the pyrolysis of nitro-organic explosives. For these reasons, much work has been done in the field of NO detection, and the need for a sensitive detector is evident. In this study, we report a direct and a highly sensitive technique to detect gaseous NO using X-ray Photoelectron Spectroscopy (XPS). The binding of NO by heme proteins is well understood2, and we have utilized it for detection. We have developed a reliable method to grow Self-Assembled Monolayers (SAMs) of alkylphosphonic acids on oxide surfaces3. This platform is used to covalently attach an iron heme-like molecule, which was synthesized separately. The N1s signal from the heme ligand was measured by XPS before and after exposure to NO. Before NO binds to the iron, a single nitrogen peak is present, attributed to the nitrogens of the porphyrin ring. After reaction with NO, a new, distinct peak was observed in the high resolution N1s spectrum. This peak is at a higher binding energy (approx 5.5 eV), and is attributed to the NO bound to the iron. An estimate of the bound NO was calculated to be about 40 picomoles. Reference: 1. R. M. J. Palmer, A.G. Ferrige, S. Moncada, Nature, 1987, 327, 524. 2. K. R. Rodgers, Curr Opin Chem Biol, 1999, 3, 158. 3. E. L. Hanson, J. Schwartz, B. Nickel, M. Koch, M. F. Danisman, J. Am. Chem. Soc., 2003, 125, 16074.


4:15 PM V7.8
Localized Surface Plasmon Resonance Biosensor for Substrate Binding to Cytochrome P450 Proteins. Jing Zhao, Richard P Van Duyne and George C Schatz; Chemistry, Northwestern University, Evanston, Illinois.

Localized surface plasmon resonance (LSPR) is one of the signature optical properties of noble metal nanoparticles. The LSPR resonant wavelength is extremely sensitive to the local environment around the nanoparticles, allowing for the development of nanoparticle-based LSPR chemical and biological sensors. Recently, the influence of resonant adsorbates on the LSPR of Ag nanoparticles was explored by mapping the LSPR wavelength change upon the adsorption of the analytes through the visible wavelength region. Both reduced and amplified LSPR response was observed when the nanoparticles’ surface plasmon couples with the molecular resonance of the adsorbates. This study provides a new approach to guide the design of biosensing chip sensors for biological targets with visible chromophores. A chip with patterned nanostructures was constructed and optimized for the detection of low molecular weight substrate/inhibitor binding to heme-containing proteins. This binding induces a change in the molecular resonances of the protein. Specifically, the heme-containing cytochrome P450 (cyt P450) proteins absorb light in the visible region (Soret absorption ~ 417 nm). When a small substrate/inhibitor molecule binds to cyt P450, the spin state/coordinating environment of the protein will change, which leads to a change in its Soret band. By fabricating nanoparticles with their LSPR that couples with the molecular resonance of P450 molecules with and without substrate/inhibitor, the response caused by substrate/inhibitor binding was monitored through a wide range of wavelengths. The most amplified response for a substrate with a molecular weight as low as ~ 150 g/mol was found to be as large as 37 nm.


4:30 PM V7.9
Fabrication of Novel Polydiacetylene-Based Microarray Chips for Label-Free DNA Detection Dong June Ahn^1,2, Doo Ho Yang¹, Eun Jin Kim¹, Gil Sun Lee^1,2 and Jong-Man Kim³; ¹Department of Chemical & Biological Engineering, Korea University, Seoul, South Korea; ²Instute for Integrated Nano Systems, Korea University, Seoul, South Korea; ³Department of Chemical Engineering, Hanyang University, Seoul, South Korea.

Polydiacetylene supramolecules are interesting biomimetic materials in view of application to chemical and biological sensors. These conjugated supramolecules are unique in changing color from blue to red upon specific binding events, caused by shortening of delocalization length of π-electrons along diacetylenic backbones. Various binding events including viruses, toxins, glucose, DNAs, proteins, and ionic interactions have been reported detectible with the forms of solution-phase vesicles and solid-supported films. However, multiplexing of various binding events has not been possible. As continuing efforts to develop polydiacetylene-based microarray chips, we have been successful in immobilization of the vesicles on solid substrate surfaces (Adv. Mater. 2003, 15, 1118) and, for the first time, in fabrication of chemical-sensing microarrays on glass by using a conventional ink-jet spotter (J. Am. Chem. Soc. 2005, 127, 17580). Each dot was found to possess the color changing property as well as the fluorescence self-emission. In this presentation, we focus on developing a novel polydiacetylene-based microarray DNA chip. Label-free detection results on sequences of E. Coli. and anthrax lethal factors will be discussed in the aspects of sensitivity as low as 10 fM and of specificity capable of discerning single-base mismatch against perfect match for SNP applications.


4:45 PM V7.10
Analyte-Induced Ordering Transitions of Liquid Crystals on Chemically Functionalized Surfaces for Reporting Chemical Warfare Agents. Katie D. Cadwell¹, Nathan A. Lockwood¹, Colin Willis² and Nicholas L. Abbott¹; ¹Chemical & Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin; ²Defense Science & Technology Laboratory - Porton Down, Salisbury, Wiltshire, United Kingdom.

This presentation will describe an experimental investigation of the orientational ordering of liquid crystals on chemically functionalized surfaces and how changes in this ordering can report the presence of vapor-phase analytes. Surfaces presenting metal ions will be shown to coordinate with liquid crystals containing suitable ligands, thus leading to micrometer-thick films of liquid crystal with orientations that are regulated by metal ion-ligand coordination interactions. Subsequent exposure of these oriented films of liquid crystal to analytes that interact competitively for metal ion coordination at the interface will be demonstrated to lead to ordering transitions in the liquid crystal. Such ordering transitions are visible to the naked eye when illuminated with white light and viewed between crossed polars. Infrared measurements provide insights into the molecular origins of the macroscopic ordering transitions that are observed when micrometer-thick films of liquid crystals supported on metal salts are exposed to organophosphorous compounds. The potential utility of these principles for simple sensing technologies will be illustrated by rapid detection of organophosphorous simulants and chemical warfare agents.


SESSION V8: Poster Session: Functional Materials for Chemical and Biochemical Sensors II
Thursday Evening, April 12, 2007
8:00 PM
Salon Level (Marriott)

V8.1
Abstract Withdrawn


V8.2
Development of Device of VOC Sensors Using Organic/MoO3 Hybrid Materials. Hiroki Yabe¹, Susumu Kajita¹, Toshio Itoh², Woosuck Shin², Noriya Izu² and Ichiro Matsubara²; ¹Advanced Technologies Development Lavoratory, Matsushita Electric Works, Ltd., Osaka, Japan; ²Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology, Nagoya, Japan.

Introduction: We are developing new volatile organic compounds (VOCs) sensors with high selectivity and sensitivity by using the layered organic/inorganic hybrids of semiconductive molybdenum oxide with organic components. A device which integrates sensor elements on a substrate can be fabricated by molding material technology. In this presentation, we report the thermal stability of the sensor materials, which is important for the design of the sensor device. Experimental section: LaAlO3 buffer layer was coated by a solution method on a silicon wafer with a thermally oxidized SiO2 insulation layer. A gold comb-type electrode was formed by a lift-off process on the buffer layer. The MoO3 thin film was prepared on the substrate by the pyrolysis of molybdenum hexacarbonyl in oxygen by CVD. The MoO3 thin film was soaked in the aqueous solution of Na2S2O4 and Na2MoO4 2H2O to reduce the MoO3 layers and to insert Na+ ions in the interlayers. Polyaniline, PANI, aqueous suspension was prepared by the polymerization of aniline. An aniline hydrochloride aqueous solution was adjusted pH value to 1.0 using HCl solution and then mixed with polymerization initiator, (NH4)2S2O8. The Na+ intercalated MoO3 film, [Na(H2O)2]xMoO3, was soaked in the PANI suspension to ion-exchange Na+ for PANI. The resulting thin film is referred to as (PANI)xMoO3. To study thermal stability of the sensor materials, (PANI)xMoO3 sensor elements were heated at 150, 200, 250, 300 degrees Celsius for 5 or 30 minutes. X-ray diffraction analysis (XRD) was carried out to estimate thermal stability of the crystallinity of the (PANI)xMoO3. Gas sensing properties of the (PANI)xMoO3 thin films to HCHO gas were measured in a flow apparatus at 100 degrees Celsius with HCHO balanced with nitrogen. The response signal was defined as the ratio of Rg/Ra, where Rg and Ra were the electrical resistances of the sensor elements in an analyte gas with nitrogen carrier gas and in only carrier gas, respectively. Results and Discussion: From XRD pattern of the substrate after CVD, deposited MoO3 thin film possessed b-axis orientation along the face of the substrate. The interlayer distance of the host was increased to 1.36nm because PANI was intercalated into the MoO3 by cation-exchange reaction. After the heat treatment at 150 degrees Celsius, XRD peaks of (PANI)xMoO3 hardly change. But at more than 200 degrees Celsius, XRD peaks were shifted to wide angle and sank down. These results mean the interlayer PANI in MoO3 was partially broken and the interlayer distance decreased with the treatment temperature and time increased at more than 200 degrees Celsius. Gas sensing property of the sensor elements, Rg/Ra, was no problem after the heat treatment at 150 degrees Celsius. Acknowledgment: This work was partially supported by New Energy and Industrial Technology Development Organization (NEDO). We would like to express our thanks for their kind support.


V8.3
Hydrogen Sensors Using Pd-based Metallic Glassy Alloys. Susumu Kajita¹, Sumiaki Nakano¹, Shin-ichi Yamaura², Hisamichi Kimura², Kunio Yubuta² and Akihisa Inoue²; ¹Matsushita Electric Works, Ltd, Kadoma , Osaka, Japan; ²Institute for Materials Research, Tohoku University, senndai,miyagi, Japan.

Pd-based metallic glassy alloys have been investigated as materials for the hydrogen sensors. We produced thin films of Pd-Cu-Si alloy known as typical metallic glassy alloys and then examined their sensitivity to hydrogen in various gas conditions. The Pd-Cu-Si thin films with different composition ratio were deposited on glass substrates by r. f. magnetron sputtering method. In order to verify the amorphicity of the thin films, an X-ray diffractometry ( XRD ) and a transmission electron microscopy ( TEM ) was used. The existence of a supercooled liquid region ( SCLR ) was measured with a differential scanning calorimeter ( DSC ). The sensitivity to hydrogen of thin films were examined by measuring the change of electric resistance of them when they were exposed to hydrogen and some other gases. Glass transition temperature ( Tg ) was 606 K to 637 K , crystallization temperature ( Tx ) was 633 K to 681K. Analyses by TEM , it showed that nano crystals existed in some films. The Pd-Cu-Si thin films were sensitive to hydrogen in wide range of hydrogen concentration (e.g. 1% to 100%) and showed rapid response to the change of hydrogen concentration. Besides their sensitivity and response time was changed by measurement temperature. It was also found that the influence of the impurity gasses such as CO, CO2, CH4 and H2O on hydrogen sensitivity changed depending on the measurement temperature. Furthermore, these thin films did not flake off from the glass substrate after the examination of hydrogen sensitivity, though the Pd-Ni crystalline thin film flaked off easily. These results indicate that the Pd-Cu-Si metallic glassy alloys have an excellent property as materials for the hydrogen sensors.


V8.4
Low temperature Fabrication of Tungsten Oxide Arrays onto Ceramic Substrates Seungwan Song¹, Insu Kang¹, Jeongmin Lee¹ and Robert S. Glass²; ¹Fine Chemical Engineering & Applied Chemistry, Chungnam National University, Daejeon, South Korea; ²Energy and Environment Directorate, Lawrence Livermore National Laboratory, Livermore, California.

A method for growing tungsten oxide films on alumina and zirconia ceramic substrates using an aqueous polytungstate solution at 75-98oC is presented. Variation in the reaction parameters of temperature, time and substrate resulted in a variation in growth morphology from round particles to square and hexagonal plates, rice, flower-like crystals and acorns arrays. The films made in solution method were active in electrochemical sensing of NO2 gas and their resistance variation was consistent with changes in gas concentration. The resultant data contribute to the applications of metal oxide films fabricated onto ceramic substrates not only to sensors but also membranes and solid oxide fuel cells.

V8.5 TRANSFERRED TO V3.28

V8.6
ppb Level Gas Sensors Based on SnO_x: M (M = Ag, Pd) Composite Nanoparticle Layers: A Comparative Study of the Effect of Metal Nanoparticle Size on Ethanol Sensing. Ivaturi Aruna and Kruis Einar Frank; Department of Engineering Sciences, University of Duisburg-Essen, Duisburg, Germany.

Gas sensors based on tin oxide are playing an important role in the detection of toxic pollutants (CO, H₂S, NO_x, SO₂ etc.) and inflammable gases (H₂, CH₄, hydrocarbons etc.) and in the control of industrial processes. The current research in the gas sensor technology is focused towards ppb level detection. Sensing at ppb level, in particular of ethanol, is important especially in breath analysers, alcoholmeters and control of spoilage of foodstuffs. Recently, sensors based on tin oxide (SnO_x) with metal additives (e.g., Pt, Pd, Au, and Ag) have drawn considerable attention.^1-4 In the present study ppb level ethanol sensors have been fabricated using monodispersed SnO_x:M (M = Ag , Pd) composite nanoparticle layers deposited using novel gas phase synthesis using aerosol route^5-7 on Si substrates with gold electrodes in which the electrode structures were bonded to a DIL-16 chip carrier through gold bond wires.⁸ The Ag (and Pd) nanoparticle size (5-20 nm) and number concentration (0-5%) have been varied (keeping the SnO_1.8 nanoparticle size constant at 20 nm) and the modifications in sensor properties (viz., the sensor signal, response and recovery time) of SnO_x:M (M = Ag , Pd) composite nanoparticle layers have been investigated and compared, at ethanol concentrations between 1 ppb and 1000 ppm in synthetic air at 400°C. An increase in sensor signal and decrease in response time with increase in Ag concentration (up to 5%) has been observed. With further increase in the Ag concentration a decrease in the sensor signal was observed. The response and recovery time were observed to decrease with decrease in Ag nanoparticle size. Sensors with Ag concentration of 5 % and particle size of 5 nm could detect ethanol as low as 100 ppb in synthetic air.⁸ These results have been compared with the SnO_1.8: Pd composite nanoparticle layers. It has been observed that the sensor’s behaviour depends strongly on the metal nanoparticle size. The enhancement in gas sensing behaviour on the addition of Ag (or Pd) in SnO_1.8 nanoparticle layers has been explained on the basis of the phenomenon of chemical sensitization due to spillover effect at the surface of the composite films. <sub>1L. Mädler, A.Roessler, S.E. Pratsinis, T.Sham, A.Gurla, N.Barsan,and U. Weimar, Sensors and Actuators B 114,283 (2006). ²A.N. Shatokhin, F.N. Putilin, O.V. Safonova, M.N. Rumyantseva and A.M. Gaskov, Inorg. Mater. 38, 374 (2002). ³O. Wurzinger and G.Reinhardt, Sensors and Actuators B 103,104 (2004). ⁴V. Lantoo and J. Mizsei, Sensors and Actuators B 5, 21 (1991). ⁵M.K. Kennedy, F.E. Kruis, H. Fissan, B.R.Mehta, S. Stappert and G. Dumpich, J. Appl. Phys. 93, 551 (2003). ⁶M.K. Kennedy, F.E. Kruis, H. Fissan, and B.R.Mehta, Rev. Sci. Instrum. 74, 4908 (2003). ⁷M.K. Kennedy, F.E.Kruis,H.Fissan, H. Niehaus,A.Lorke and T.H. Metzger, Sensors and Actuators B 108, 62 (2005). ⁸R.K. Joshi and F.E. Kruis, Appl. Phys. Lett. 89, 153116 (2006).


V8.7
Hydrogel Based Composite Materials for Chemical, Biological and Medical Sensing Applications. Tim Porter¹, Jim Reed², Ray Stewart² and Kathryn Morton²; ¹Physics, Northern Arizona University, Flagstaff, Arizona; ²Cantimer, Inc., Menlo Park, California.

Various hydrogels, functionalized hydrogels and hydrogel composite materials may be used as the active sensing material is embedded piezoresistive microcantilever (EPM) sensors. Depending on the sensing application, the sensing material is designed to physically or chemically respond to the desired analyte, resulting in signal transduction through the microcantilever. Previous EPM sensor designs have demonstrated rapid responses to a variety of chemical and biological species, including volatile organic compounds, carbon monoxide, hydrogen cyanide gas, single-strand DNA, certain proteins, vaccinia virus, and others. In the present application, we describe the use of a functionalized hydrogel material in a small, handheld personal hydration sensor. This sensor is designed to respond to changes in solution osmolality, thus providing a rapid, intraoral, and non-invasive method of measuring an individual's hydration state. The sensing material responds volummetrically to the analyte through the partitioning in of fluid species owing to osmotic pressure and membrane diffusion into the gel volume. Stable signals are generally obtained after 30 seconds of exposure. After an osmolality sensing event, the sensor material may fully recover to its original state through immersion in a standard solution of known osmolality. Applications for this sensor include pediatric hydration assessment, geriatric hydration monitoring, and various sports monitoring applications.


V8.8
Abstract Withdrawn


V8.9
Enhanced Gas Sensing Properties of In2O3:Ag Composite Nanoparticle Layers: Size and Interfacial Effects Vidhya nanad Singh¹, Bodh Raj Mehta¹ and F. E. Kruis²; ¹Thin Film Laboratory, Department of Physics, Indian Institute of Technology, New Delhi, Delhi, India; ²Nanostrukturtechnik, University of Duisburg-Essen, Duisburg, NRW, Germany.

Gas sensor studies on oxide semiconductors nanoparticle layers prepared by different synthesize method has been reported in literature. In most of these studies, the parameters which are used to control nanoparticle size also vary other properties like film thickness, composition and porosity. Metal additives used to enhance the gas sensing response are present in undefined metal-semiconductor configurations with metal present as small or big clusters, thin or thick layers. In the present work, role of nanoparticle size and Ag additive in controlling the gas sensing properties of In2O3:Ag composite nanoparticle has been studied. For this purpose, In2O3:Ag composite nanoparticle layers having well-defined individual (In2O3 and Ag) nanoparticle sizes (10-25 nm) and composition (0-25 %) have been grown using a two-step synthesis process of dip coating using chemically grown nanoparticles as precursors¹. In2O3, Ag and In2O3:Ag nanoparticles have been characterized using X-ray diffraction, optical absorbance, transmission electron microscopy and X-ray photoelectron spectroscopy techniques. A size-induced lowering of temperature of phase-transition from In(OH)3 to In2O3 nanoparticles has been observed without the normally present effects of agglomeration and size alteration during the transformation, for the first time². The improvements in the gas sensing properties have been understood in terms of relationship between the size and depletion layer thickness³. Gas-sensing studies of In2O3:Ag layers as a function of Ag composition, ethanol concentration and operating temperature have been carried out. In2O3 composite nanoparticle layers with 15 % silver show a high sensitivity of 436 and a low response time of 6 second for 1000-ppm of ethanol in air⁴. A detailed energy level diagram of the composite nanoparticle structure in the oxidizing and reducing environments has been proposed. The results have been explained in terms of electronic enhancement due to change-over from a depletion-type to accumulation-type interface at the nanoparticle boundaries. These results are consistent with the results of X-ray photoelectron spectroscopy studies. References 1. V. N. Singh and B. R. Mehta, Jap. J. Appl. Phys 42 (2003) 4226. 2. V. N. Singh and B. R. Mehta, J. Nanosci. Nanotechnol. 5 (2005) 437. 3. B. R. Mehta and V. N. Singh, Pramana- J. Phys. 65 (2005) 949. 4. V. N. Singh, B. R. Mehta, R. K. Joshi, F. E. Kruis and S. M. Shivaprasad, J. Nanosci. Nanotech. (in-press) Acknowledgements: The work was carried out with the financial support provided by the Council for Scientific and Industrial Research (CSIR), New Delhi, India (Grant No. 03(0995)/04/EMR-II).


V8.10
Abstract Withdrawn


V8.11
Abstract Withdrawn


V8.12
Abstract Withdrawn


V8.13
Abstract Withdrawn


V8.14
Abstract Withdrawn


V8.15
An Organic Electronic Ion Pump to Induce Intracellular Signalling in Living Cells. Magnus Berggren¹, Agneta Richter-Dahlfors², Joakim Isaksson¹, David Nilsson³, Peter Kjall² and Nathaniel Robinson¹; ¹ITN, Linkoping University, Norrkoping, Sweden; ²MTC, Karolinska Institutet, Stockholm, Sweden; ³Printed Electronics, Acreo AB, Norrkoping, Sweden.

In devices based on conjugated polymers ions can act as the signal carriers besides the electrons. Also, the electronic conduction character in the bulk of conjugated polymers is altered, reversibly or permanently, as its electrochemical state is switched. In the past this phenomenon has been used to construct electrochemical transistors for sensing and logics. Here, we report further developments of these polymer electrochemical transistors towards electronic ion pumps to stimulate living cells. This electronic ion pump includes the electroactive polymer PEDOT. As the electrodes are addressed of this ion pump, ions from one electrolyte migrate to another and are launched at high spatial resolution from a polymer electrode surface. We have chosen to study pumping of Ca2+ and K+ due to their great relevance in biology. HCN-2 neuronal cells were grown along the ion emitting electrode and we observed induced intracellular signalling responses as a consequence of addressing the electronic ion pump. Such pumping events were found to occur at high enough temporal and spatial resolution associated with several important physiological events in cells.


V8.16
Novel Investigation of Ozone Sensor Based on Porous Silicon. Rathinasamy Prabakaran, Department of Materials Science and CEMOP/UNINOVA, CENIMAT, Caparica, Caparica, Portugal.

Porous silicon (PS) is an interesting base material to develop a gas sensor due to its high surface to volume ratio and its high reactivity. Further, the electro-physical quality of a PS surface/interface depends on the degree of dangling-bond passivation. In particular, hydrogen and/or oxygen/ozone related surface passivation of electrochemically etched silicon plays a vital role in determining the sensing properties of PS. Until now, numerous investigations have been carried out to understand the various chemical mechanisms involved in the fabrication PS gas sensors; however, an inadequate attention is paid on their ozone sensing properties, especially under UV light exposure in vacuum condition. The present work illustrates a new landmark in the fabrication of ozone sensor based on PS. The responses of ozone sensing from the conductivity measurement using Al/PS/n-Si/PS/Al in co-planar contacts has been investigated. In the presence of ozone the dark conductivity (σd), of PS decreases about 3 orders of magnitude. This behavior is related to the oxidation of the porous silicon surface, but process is reversible in the presence of UV light exposure, which makes possible application towards ozone sensor. In addition, the transport of the charge carriers via a tunneling mechanism is also studied from the current-voltage characteristic of an Al/PS/n-Si/Al device. Furthermore, detailed characterization analyses are done to understand an inherent nature of this PS material type using XRD, FTIR, micro-Raman, SEM and AFM techniques. The Raman scattering from optical phonon in this PS specimen showed downshift of the phonon frequency, broadening and increased asymmetry of the Raman mode. Using the phonon confinement model, the average diameter of Si nanocrystallites present in PS is estimated. The size estimated from Raman spectrum and XRD pattern are in good agreement and compared well with the estimated size from AFM. Finally, we have correlated all the aforesaid results for optimizing good ozone sensor PS device.


V8.17
Copper Phthalocyanine Organic Nanowires as a Prospective Platform for Chemical Sensing Evghenii Strelcov, Seghei Dmitriev and Andrei Kolmakov; Physics, SIUC, Carbondale, Illinois.

Copper phthalocyanine (CuPc) - an organo-metallic compound that exhibits a unique combination of chemical, electrical and optical properties which are practically important for gas sensing, as dyes, photosensitisers and catalysis. In the form of thin films this material is widely used as gas sensing media for the detection of environmental polluting gases such as NOx. It was proposed that quasi 1D morphology of metal phthalocyanines can drastically improve the sensitivity and response time of these sensors. The conditions to synthesize CuPc nanowires and whiskers were explored and it was found that morphology and polymorphism of deposited material is highly sensitive both to the temperatures of the source and substrate and deposition time. At lower temperatures (RT) growth of solid film was observed followed by novel web-like nanostructure at middle temperatures (<140 0C) and single nano and meso whiskers at high temperatures (>140 0C). 2D web-like nanostructure manifests excellent adhesion to different oxide substrates which is a strong advantage for gas-sensing device preparation. All said morphologies along with phthalocyanine powder were characterized by XRD, UV-VIS spectra and SEM techniques, what allowed us to propose a growth model. Gas-sensing devices on the basis of all three morphologies were prepared and comparative study was accomplished. It was shown that these possess high sensitivity towards NOx, quite low sensitivity towards ammonia and negligible sensitivity towards oxygen and hydrogen. Comparison of data obtained in real world conditions (in air flow) and model ones (in vacuum) for different morphologies was performed.


V8.18
Resist Free Fabrication of Metal Oxide Nanowire Gas Sensors Bradly Button¹, Yigal Lilach³, Victor Sysoev², Serghei Dmitriev² and Andrei Kolmakov¹; ¹Physics, SIUC, Carbondale, Illinois; ²Physics, Saratov State Technical University, Saratov, Russian Federation; ³PNNL, Richland, Washington.

Quasi 1-D metal oxide semiconductors demonstrate excellent gas sensing capabilities which are dependent upon the specific surface chemistry, as well as the size (diameter) and shape (morphology) of the bulk metal oxide. Morphological variations in the oxide structure influence the sensing performance which is attributed to the surface to bulk (S/B) carrier concentration ratio in conjunction with the ratio of the Debye screening depth, LD and the effective size of the conduction channel, D due to the surface interactions with the sensor’s ambient environment of either an oxidizing or reducing nature. These factors dominate the effective size of the conduction channel of the oxide structure and therefore sensitivity. In this report we describe the resist free fabrication and comparative sensing performance of the individual nano and meso wire devices based on SnO2, In2O3, and TiO2 structures for practical senor applications.


V8.19
Adhesion Force of Avidin Molecules on Well-ordered Solid Surfaces. Ryuji Aoki, Taro Arakawa and Toshio Ogino; Dept. of Electrical and Computer Engineering, Yokohama National University, Yokohama, Japan.

Immobilization of bio-molecules on solid surfaces is one of the key issues in high-density, high-sensitivity biosensors. In particular, adhesion stability of bio-molecules on the substrate surfaces is important for reliable bio-sensing. We characterized adhesion forces of avidin (protein) molecules to sapphire surfaces in water as well as in air by using the frictional force mode in atomic force microscopy (AFM). It was found that the chemical states of the surfaces strongly influence the stability of the molecule adsorption. Sapphire is a chemically stable material as a substrate for bio-sensing devices. In this work, we used step-bunched sapphire surfaces exhibiting wide terraces. This surface was fabricated by a high temperature annealing in a hydrogen atmosphere. By using the well-ordered surfaces, we can estimate the adhesion force more accurately. The substrates were cleaned by a mixture of sulfuric acid and hydrogen peroxide. A hydrophilic surface is obtained by this process. To prepare a hydrophobic surface, we used self-assembled monolayers of octadecyltrichlorosilane. Avidin molecules were adsorbed on the surfaces by immersing the substrates in the avidin-containing water. The adhesion force can be qualitatively estimated from whether any movement of the molecules is observed or not after the frictional mode scanning. The stability of physically adsorbed avidin molecules in air was examined with the tip force of 22 nN. It was found that the avidin molecules are tightly bound on the surface. This strong adhesion force was observed both in the hydrophilic and the hydrophobic surfaces. Avidin molecule movement in water was found to be much different. On the hydrophilic surfaces, the whole avidin molecules were removed from the scanning area after the contact-mode scanning even with the tip force of 0.044 nN. This is reasonable because a water layer exists between the avidin molecules and the hydrophilic surfaces. On the hydrophobic surfaces, on the other hand, the avidin molecules were not moved by the scanning with the tip force of 0.044 nN. When the tip force was 0.44 nN, avidin molecules disappeared probably due to attachment of the avidin molecules to the tip surface. When another area was scanned after the disappearance of avidin molecules using the same tip, it was observed that some avidin clusters became larger. This is probably due to the detachment of the molecule from the tip and the attachment to the cluster. This result suggests that adhesion force between an avidin molecule and a hydrophobic sapphire surface in water is comparable with the tip-molecule interaction. In summary, the physical adsorption of avidin molecules in water is much weaker than in air and strongly influenced by the surface chemical states.


V8.20
Characteristics of Electrochemical CO2 Sensor Based on Thin Film Conducting Electrolyte Combined with Thick Film Components. Woon Young Lee¹, Jinseong Park², Haegun Shin², Dong-won Park¹ and Yong-Kook Choi¹; ¹Chonnam University, Gwangju, South Korea; ²Chosun University, Gwangju, South Korea.

Li⁺ ion conducting Li3PO4 thin film electrolyte with thickness 1.2μm was deposited on Al2O3 substrate by thermal evaporation method. Au electrodes were deposited on the electrolyte by DC magnetron sputtering. Reference and sensing electrodes were printed on Au interfaces by conventional screen printing technique. The electromotive force (emf) and Δemf/dec values of the sensor are dependent on the thickness and sintering temperature of the electrolyte thin film. 1.2μm thickness deposited and 775°C sintered electrolyte has shown good sensing behavior than the sensors with less thickness and sintering temperatures. Similarly, the thickness of the sensing and reference electrodes was optimized at 10μm. It is observed that the triple point concentration arising at the electrolyte, electrode and Au interface has been increased and led to the increased stability of the sensor as a result of reversible electron transfer. The heater resistance which plays a vital role in the smart device fabrication was controlled by the heater pattern and thickness of the Pt film without laser trimming.


V8.21
CMOS Micro Humidity Sensors Using Nano-structured Carbon Nitride Film Sungpil Lee¹, Jigong Lee¹, Sungyeop Kim¹, Choongwon Chang¹ and Chongsoo Mun²; ¹Electronic Engineering, Kyungnam University, Masan, Kyungnam, South Korea; ²Advanced Materials Engineering, Kyungnam University, Masan, Kyungnam, South Korea.

CMOS micro humidity sensors with nano-structured carbon nitride film as humidity sensing materials are fabricated by 0.8 μm standard CMOS process and porous gate metal formation, and their threshold voltage and drain current drift are investigated according to the relative humidity change. Integrated sensor system consists of humidity sensor, temperature sensor, Hall sensor and OP amp. The micro humidity sensor has several type, such as conventional n-type and p-type FET, n-type and p-type interdigital gate and combined bridge structure. Gate length of sensor is 8 μm, chip size is 2x4 mm and pin number is 28, respectively. The sensor part is consisted of a pair of transistors, that is, humid-sensitive transistor and non-sensitive one. The aspect ratio is 300/8 for both transistors to get same current-voltage characteristics and to compare a drift of drain current to humidity changes. Nano-structured carbon nitride (CNx) films as humidity sensing materials on the gate insulator are prepared by reactive RF magnetron sputtering with a DC bias at various deposition conditions. When water molecules meet carbon nitride layer through the porous gold layer of FET gate, they are chemisorbed on the available sites of the carbon nitride surface by dissociative mechanism to form two hydroxyl ions for each water molecule, which possess high local charge density and a strong electrostatic field, and the proton reacts with an adjacent surface O2- group to form a second OH- group. Therefore singly bonded water molecules are able to form dipole and to reorient freely under an externally applied gate field, resulting in an increase in the dielectric constant. It is caused by an increase of capacitances in sensing materials. This is attributed to the threshold voltage changes and the drain current increases of micro humidity sensors. The fabricated humid non-sensitive MISFET, that is, reference MISFET presents the typical enhancement mode characteristics. The humidity sensitive MISFET shows that the normalized drain current linearly increases from 0.124 to 0.415 in the range of the relative humidity from 30% to 95%. The normalized value of the drain current can be used as a sensitivity of the humidity sensitive field effect transistor.


V8.22
Hydrogen Sensors Based on Cu/Pd Bimetal Layers. Manika Khanuja¹, Bodh Raj Mehta¹ and Sonnada M. Shivaprasad²; ¹Physics, Indian Institute of Technology Delhi, New Delhi, Delhi, India; ²Surface Physics and Nanostructures, National Physical Laboratory, New delhi, Delhi, India.

Surface properties of a material play a crucial role in deciding metal-adsorbate interaction. In this direction, bimetallic surface provides a convenient way to enhance the given metal-adsorbate interaction by combining properties of the two elements in a synergic fashion to yield a new surface, which is more reactive than the two individually. In the present study, we propose a Cu/Pd bimetal layer based novel material for H-sensing applications. This study can also form the basis for future efforts in the field of Pd based bimetallic sensors using different metal adlayers. Palladium (Pd) is known to have immense potential as a hydrogen-sensing element due to its high permeability, high catalytic activity for H2 dissociation, high solubility, rapid diffusion of interstitial H and exclusive selectivity for hydrogen. In the present work, Pd surface has been modified by forming Cu/Pd bimetallic system using the technique of physical vapour deposition. This modifies the electronic structure of Pd significantly, leading to tunable H chemisorption properties. Hydrogen sensing response of the modified Pd surface has been studied in terms of change in electrical resistance during hydrogen loading - deloading cycles. The surface electronic structures are probed as a function of copper layer thickness and annealing temperature by examining core level shifts and valance band spectra as determined by X-ray photoelectron spectroscopy (XPS). Valance band can be structured in (i) a Pd dominance in the low-BE region, (ii) an intermixing range where hybridization of Pd 4d and Cu 3d bands takes place, which is enhanced by annealing, and (iii) the Cu 3d band influence in the high-BE region. Formation of new states in the valance band at temperature higher than 450 K is a signature of Pd-Cu surface alloy formation. The changes in the valance band spectra with annealing temperature effects hydrogen sensing response of Cu/Pd bimetal layer. The XPS data show the formation of hetronuclear Pd-Cu bond that induced a flow charge from Pd to Cu due to large number of empty states in the Cu valance band. Thus a shift of about 1.0 eV in the Pd valance band is observed which increases the d-band coupling matrix and overlap of H-1s and Pd-4d levels. Effect of modified valance band on the hydrogen sensing response has been explained in terms of density of states at the Fermi level and d-band centroid position. Hydrogen induced resistance change is found to be reversible and stable in the studied system.


V8.23
Near-Infrared Sensitive Photorefractive Bifunctional Dendrimers Operating at 830 nm Kyung Moon Jung, Sang Kyu Lee, Min Ju Cho and Dong Hoon Choi; depratment of chemistry, korea university, Seoul, South Korea.

During the past decade, photorefractive (PR) organic materials have received considerable attention due to their low cost, easy processability, and possibility of manipulation of PR properties by chemical modifications. While most studies of PR polymers and organic glasses were carried out in a visible wavelength region, the extension to near-infrared (NIR) wavelengths has several advantages, which include the use of low-cost semiconductor diodes available at many NIR wavelengths, and the tissue transparency window at 700-900 nm in biological applications. The PR wavelength sensitivity is embedded in the photogeneration process, and is usually determined by a sensitizer added to the PR material composite and its interactions with the other components of the composite. In most NIR studies, PR sensitization is achieved using (2,4,7-trinitro-9-fluorenylidene)malononitrile (TNFM) as a sensitizer. New bifunctional dendrimers C-TCP-Cz and C-Cz-TCP were synthesized successfully. C-TCP-Cz and C-Cz-TCP have three functional dendrons. The difference of dendrimers is the order of Cz and TCP. C-TCP-Cz has the carbazole unit at the outermost peripheral position. NLO chromophore exists at the terminal peripheral unit in C-Cz-TCP. The chemical structures of the new bifunctional dendrimers were characterized by 1H NMR spectrometer. The flexible six methylene spacer and 1st-generation dendrimer are designed to reduce the glass transition temperature. So the glass transition temperatures of C-TCP-Cz and C-Cz-TCP were 44oC and 29oC at heating rate of 10oC/min. We prepared the thick PR samples by using C-TCP-Cz and C-Cz-TCP. PR sample was fabricated using C-TCP-Cz and TNFM. The solution prepared in monochlorobenzene was filtered through an acrodisc syringe filter and then cast on indium-tin-oxide (ITO) pre-coated glass. The film was dried overnight at 100oC under vacuum. After the solvent had been removed completely, another ITO glass was placed on top of the film and pressed down at 150 oC with a 60-µm polyimide film as a spacer to get a sandwich device for two-beam coupling (2BC) experiments. The net gain of one of the dendrimers, C-Cz-TCP was determined about 80-100 cm-1.


V8.24
Bottom-up Creation for Antibody with High Affinity for Inorganic Materials Mitsuo Umetsu, Takamitsu Hattori, Takeshi Nakanishi and Izumi Kumagai; Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Sendai, Japan.

Recent advance in biotechnology enables us to find the peptides with affinity for nonbiological materials and with function of mineralizing inorganic materials. The recognition of peptide/protein for material surface, especially, the specific binding on inorganic materials, is attracting a growing interest as an indispensable tool for the fusion between biotechnology and nanotechnology. The peptide/protein with excellent binding ability and specificity for an inorganic compound and its crystal structure, enables to directly immobilize and pattern biomolecules on the corresponding inorganic nanoparticles and substrates, and further, to control the crystal structure growth in the inorganic synthesis process. Antibody is a naturally occurring recognition molecule with high binding ability and specificity in immune system. In general, antibody have high affinity at the dissociate constant of ~nM, and it can be expected to be superior to that of a low-molecular weight peptide showing relatively low affinity to its target surface. Here, we append the affinity for inorganic material to antibody by replacing the complementarity determining regions (CDRs) of antibody with a specific peptide for the corresponding material. The utilization of the peptide for innovating antibody would open the way to convenient preparation for the antibody against non-biomaterials. We would show the possibilities of the CDR-grafting technique for the innovation of the antibody with affinity for non-biomaterials, and further, the maturation of the grafted antibody to the bio-interface molecule with high affinity by phage display technique.


V8.25
An Overview of Polydiacetylene Optical Strain Sensors. Jennifer Kauffman¹, William T. Pennington², Michael S. Ellison¹ and Timothy W. Hanks³; ¹Materials Science & Engineering, Clemson University, Clemson, South Carolina; ²Chemistry, Clemson University, Clemson, South Carolina; ³Chemistry, Furman University, Greenville, South Carolina.

Polydiacetylene polymers are known for their dramatic colorimetric detection abilities. When formed in a solid-state polymerization, the backbone of the polymer is planar and continuous π-overlap is observed. However, when an outside force is imposed on the system the backbone contorts, breaking the conjugation length and providing an optical shift. The state of the backbone has been monitored quantitatively through Raman spectroscopy. Several novel strain sensing systems have been created and subjected to simultaneous tensile testing and Raman scans. A few of these systems include copolyurethane-diacetylene polymers cross-polymerized with UV, hydrogen-bonded polymer blends of 4-butoxymethylcarbonyl urethane in several industrial polyurethanes (ex. Tecoflex®, Lycra®, Minwax®, etc.), and finally polydiacetylene cationic and anionic dyes that have been bound electro-statically to acrylic and wool, respectively. A linear trend has been established between the Raman -C≡C- stretch peak of the polydiacetylene (~2100cm-1) and the percent strain detected from the system. It has been determined that similar strain sensing capabilities are available from the polymer blends as compared to the copolymer systems.


V8.26
Development of an Immunoassay for Monitoring Tissue-Specific Function in Cellular Micropatterns. Caroline Noelle Jones, Ji Youn Lee and Alexander Revzin; Biomedical Engineering, UC Davis, Davis, California.

Surface micropatterning approaches have been utilized extensively for investigating the effects of cell-cell and cell-surface interactions on the expression of cell phenotype. More recently, robotic microarraying approaches have emerged as tools for combinatorial screening of cell-microenvironment interactions. The emergence of cell culture approaches that provide multiple biological stimuli in the same cell culture dish necessitates the development of new methods for evaluating local cell function in the context of a complex microenvironment. The present project seeks to develop an immunoassay for local detection of tissue-specific proteins in micropatterned hepatic cells. Glass surfaces were patterned with cell-adhesive proteins (e.g. collagen (I)) using robotic printing or photolithographic approaches. Glass surfaces were then incubated with an anti-albumin antibody, resulting in formation of discrete micropatterned domains for cell-adhesion and albumin binding. When seeded onto the surface, hepatic cells (HepG2 cells) became spatially localized to matrix protein domains and started secreting liver-specific proteins such as albumin. Secreted albumin was then captured by the antibody molecules immobilized around cellular clusters. Binding of the albumin was verified by fluorescently- or HRP-labeled secondary antibody. The proposed surface micropatterning approach enabled local detection of tissue-specific proteins secreted by hepatic cells. This approach may offer a new tool for monitoring local phenotype of cells exposed to a complex, microfabricated environment.


V8.27
Inorganic Electride Films as Potential Electro-optic Sensors Georgi Diankov and Andrew S. Ichimura; Chemistry and Biochemistry, San Francisco State University, San Francisco, California.

Zeolites are microporous crystalline solids that have traditionally found applications in exchange, separations, and catalytic processes. These diverse applications originate from the 'molecular' pore size of 5-7 Å, the robustness of the framework and the ability to withstand high temperatures, as well as the variable composition (depending on zeolite type) from pure silica to materials with equal molar ratios of Si and Al ([M⁺AlO2^-]x[SiO2]1-x; x≤0.5]. Recently, zeolites have received considerable attention as potential chemical sensors prepared as supported thin films, using substrates such as an ATR crystal or the end of a quartz optical fiber.^1,2 Our interest in sensing applications involving zeolites takes a different approach and stems from the unique optical and electric properties of alkali metal doped silica zeolites, which are referred to as M@SZ where M = Na-Cs and SZ is an all-silica zeolite.^3,4 In this report, the properties of M@SZ prepared as bulk powders and thin films supported on Au, Si, quartz and ITO are explored through optical (IR, UV-vis-NIR) reflectance and transmission spectroscopy, X-ray diffraction, HRSEM, solid-state MAS NMR and AFM. For this study, zeolite MFI (silicalite, ZSM-5) was chosen because films of pure silica material are straightforward to synthesize. Optical reflectance measurements on powders show that Cs@MFI exhibits a broad NIR peak that increases in intensity with increasing Cs concentration. The NIR band is evidence for free electrons trapped in the zeolite pores.^3,4 Cs-doped MFI films also exhibit the NIR band, but significantly, the absorption intensity increases toward the NIR as would be expected if the sample were metallic. Packed powder conductivity measurements show that bulk samples are insulating due to grain boundary effects. It is hypothesized that the continuity of the polycrystalline MFI film may permit electron transport through the pore structure of Cs@MFI, as predicted by density functional calculations.⁵ Conductivity measurements on M@MFI films are in progress. Because the free electron NIR band is intrinsic to M@SZ materials, it is envisioned that thin M@SZ films could function as NIR transducers and find applications as sensors or as integral components of electro-optic technology. 1. Bein, T. Chem. Mater 1999, 8, 1636-1653. 2. Zhang, J.; Luo, M.; Xiao, H.; Dong, J. Chem. Mater. 2006, 18, 4-6. 3. Ichimura, A. S.; Dye, J. L.; Camblor, M. A.; Villaescusa, L. A. J. Am. Chem. Soc. 2002, 124, 1170-1171. 4. Wernette, D. P.; Ichimura, A. S.; Urbin, S. A.; Dye, J. L. Chem. Mater., 2003, 15(7), 1441-1448. 5. Li, Z.; Yang, J.; Hou, J. G.; Zhu, Q.; J. Am. Chem. Soc., 2003, 125, 1170-1171.


V8.28
Abstract Withdrawn


V8.29
Synthesis, Characterization and Modification of Fe3O4 Nanoparticles and their Application in DNA Sequence Detection. Jin Xie, Brown University, Providence, Rhode Island.

Monodisperse FeM2O4 (M=Fe,Mn,Co) nanoparticles with sizes tunable from 3-16 nm were synthesized through easy, one-pot reaction. Next, either through ligand exchange or ligand addition, with the help of the commercially available phospholipids or the PEG based ligands synthesized, those as-synthesized, hydrophobic particles could be transformed to be well dissolved in water and were ready for further modification. The characterizations of the particles before and after modification were done, and the structures were studied. The stability of the particles in buffer solution was proved to be very good even after cooking at 70°C for 24 hours. These particles were then conjugated with single strand DNA, and applied on modified Si wafers. The specific bonding of the particles was achieved and was detected by GMR sensor. We are working at using these magnetic particles as tags instead of the traditional organic dyes to do the mircoarray, which potentially provide higher sensitivity with lower price.


V8.30
Fabrication and Characterization of Individual Nanotube Based Nanoelectrodes for Chemical and Biological Sensing. Kyungsuk Yum and Min-Feng Yu; Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois.

We present the fabrication and characterization of individual nanotube based high length-to-diameter aspect ratio nanoelectrodes for chemical and biological sensing. The nanoelectrodes are fabricated by coating insulating nanotubes with metal, such as gold and silver, subsequently coating them with thin insulating layers, and cutting the end of the nanoelectrodes. The process yields ring-shaped nanoelectrodes, with the thickness of the ring of ~ 10 nm, whose electrochemically active area is controlled by the metal deposition. The nanoelectrodes have a total structural diameter of ~ 100 nm, including insulating layers, and length up to ~ 30 µm. The nanoelectrodes are characterized by cyclic voltammetry (CV) and square wave voltammetry (SWV), and the structure of the nanoelectrodes is further examined in transmission electron microscope (TEM). The nanoelectrodes show steady-state voltammetric current responses and good insulation of the side wall of nanoelectrodes. The high length-to-diameter aspect ratio nanoelectrodes will allow a new opportunity for electrochemical sensing in microscale environments, e.g. in vivo probing local intracellular environments without damaging cells, with high temporal and spatial resolution.</sub>

SESSION V9: New Approaches on Gas Sensing
Chairs: Elisabetta Comini and Vincenzo Guidi
Friday Morning, April 13, 2007
Room 2008 (Moscone West)
8:30 AM *V9.1
Smart SOI-based Gas Sensors Employing Nanomaterials. Julian William Gardner¹ and Florin Udrea²; ¹School of Engineering, Warwick University, Coventry, United Kingdom; ²Engineering, Cambridge University, Cambridge, United Kingdom.

This invited paper presents recent work towards a new generation of smart gas sensors based upon silicon-on-insulator (SOI) CMOS technology and nanomaterials. Firstly, we review briefly the current and emerging markets for gas sensors and the different types that are commercially available today. From this comes the demand for lower-cost, lower-power gas sensors and hence drive towards developing silicon micro-machined gas sensors. Next we present our work towards a new generation of gas sensors based upon silicon-on-insulator (SOI) CMOS technology. Low-power resistive and calorimetric SOI gas sensors are described with full 3-D models of electrical, thermal, and mechanical (stress) characteristics. These CMOS devices offer various types of micro-heater, such as FET, single-crystal silicon (n+/p+), polysilicon, and tungsten. We show that an SOI gas sensor can have a power consumption of much less than 1 mW at 500°C together with a thermal response time of less than 1 ms. In addition, we describe integrated temperature sensors and circuits for smart SOI CMOS gas sensors. Finally, we discuss the use of different nanomaterials in gas sensing and, in particular, our work on the combination of certain nanomaterials with SOI devices, such as carbon nanotube composites, tungsten nanoneedles, and palladium nanorods.


9:00 AM V9.2
Tunable Plasmon Resonant Sensor Arrays Amitabh Ghoshal¹, Pieter G Kik¹, Karthik Kardivel² and Toshikazu Nishida²; ¹CREOL/The College of Optics and Photonics, University of Central Florida, Orlando, Florida; ²Electrical and Computer Engineering, University of Florida, Gainesville, Florida.

The field of surface plasmon resonance (SPR) based chemical detection has been rapidly growing over the past decade. Commercial SPR sensors have been developed and single molecule detection has been achieved using Surface Enhanced Raman Scattering on metal nanoclusters that support highly localized plasmon resonances. Although the use of localized resonances is attractive for array based bioassays, it has proven difficult to reproducibly generate structures that support the necessary high field enhancements at the desired frequency. In this presentation we discuss a micro-electro mechanical device design that enables control over the resonance frequency of metal nanoparticles by means of mechanical action. The device consists of a regular array of gold nanoparticles generated by e-beam lithography on a quartz substrate. The as deposited gold nanoparticles exhibit a surface plasmon resonance wavelength of $\sim$500 nm. A movable transparent membrane coated with a 50nm thick Si film is suspended above the nanoparticle array. The physical separation between the membrane and the array can be adjusted electrically by capacitive coupling, providing control over the local dielectric environment of the nanoparticles. The high refractive index of the Si film when brought in close proximity to the metal nanoparticles affects the local polarizability, resulting in a frequency shift of the surface plasmon resonance. Analytical calculations suggest a wavelength tuning range in excess of 100nm. It is shown by means of numerical simulations based on the Finite Integration Technique that the experimentally accessible tuning range depends sensitively on the polarization of the incident light. The details of the device design and fabrication will be discussed, and measurements of the gold nanoparticle resonance frequency as a function of membrane displacement using in-situ dark field spectroscopy will be presented. The practical implementation of such tunable plasmon resonant scatterers for chemical sensing will be discussed.


9:15 AM V9.3
Electroactive Chemo-Actuators Aisha S Haynes^2,1, Smita Gadre¹ and Perena Gouma¹; ¹Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, New York; ²Launcher Technology, U.S. Army RDECOM Benet Laboratories, Watervliet, New York.

This paper details the design of a chemical actuator based on polyaniline. Composite hybrids of polyaniline and cellulose acetate are manufactured by drop-coating and electrospinning to produce thin films of the polymer with high surface area and high porosity. Exposure to organic vapors has eluded changes in the conformational structure of the conducting polymer yielding displacement of the composite film upon adsorption of the vapor and restoration to initial state upon desorption. Chemical and morphological analyses of the films define the actuating character of the composites to be a function of the morphology of the hybrid and the adsorption/desorption behavior of polyaniline in the presence of organic vapors.


10:00 AM *V9.4
Development and Application of Gas Sensing Technologies For Combustion Processes Prabir Dutta, Chemistry, The Ohio State University, Columbus, Ohio.

The Center for Industrial Sensors and Measurements at The Ohio State University is developing ceramic-based microsensors to monitor total NOx, CO, CO2, O2 and hydrocarbons at temperatures of 500-700oC. Successful creation of miniaturized gas sensor systems will dramatically alter how combustion systems are operated and optimized. Sensor systems with fast response times should allow integration with controlling algorithms. Our approach in designing highly selective sensors is centered on the appropriate choice of the sensing principle, novel materials and use of catalysts. For O2 sensing, potentiometric measurements across a yttria-stabilized-zirconia with metal/metal oxide internal reference and a novel sealing technology is being developed. A potentiometric design is also the basis for a total NOx sensor, where a catalyst filter minimizes interference of CO and converts NO/NO2 to a total equilibrium NOx value. CO sensing is being done with resistive titania sensors, modified by catalysts and/or pn composites to produce selectivity and sensitivity. Hydrocarbon sensing exploits a filter that oxidizes the hydrocarbon to water, which is then sensed on titania. Miniaturized versions of these sensors are being integrated into a sensor array with data analysis by non linear regression techniques.


10:30 AM V9.5
Abstract Withdrawn


10:45 AM V9.6
Mercury Detection with Monodispersed and Size-controlled Au/Ag Nanoparticle Ensembles Synthesized on Nanostructured Si Films. Kaan Kalkan, Oklahoma State University, Stillwater, Oklahoma.

Mercury is a severe neurotoxin whose contamination in the environment has jumped threefold since the beginning of the industrial revolution. Coal-fired power plants are the major emitters of mercury, which enters the food chain via the air and water. With the emergence of surging economies around the globe and the resulting demands on oil supplies, coal usage and, therefore, the potential for further mercury contamination are increasing. To monitor mercury levels, quick reliable means of both elemental and ionic mercury detection are needed. This work demonstrates a novel surface plasmon resonance mercury sensor capable of detecting both elemental and ionic mercury in air and water down to ppb levels in minutes. This sensor consists of ensembles of Au or Ag nanoparticles, which are synthesized on plasma deposited nanostructured columnar Si films simply by film immersion into pure Au/Ag salt solutions. In addition to functioning as a reducer, the nanostructured Si provides immobilization and monodispersion of the Au/Ag nanoparticles due to its systematic nanoscale topography without the requirement of a surfactant, capping agent, or linker. The absence of such agents on the nanoparticle surfaces is a substantial benefit that provides unlimited access for the adsorption of mercury accounting for the ultrasensitive and ultrafast detection observed. The plasmon extinction peak increases in intensity, broadens, and shifts towards lower wavelengths in response to mercury’s adsorption. In particular, at 20 ppb mercury, the shift is 4 nm in the first 5 minutes with Au nanoparticles (average size is 20 nm). The total shift (at saturation) as well as the kinetics of the shift has a dependence on mercury concentration which can be readily used to measure mercury levels. Unlike the nanostructured columnar Si, flat Si surfaces lead to Au/Ag nanoparticle synthesis (only in the presence of HF) with no control over particle size and aggregation resulting in multiple resonances of the plasmon extinction which are less susceptible to frequency shift upon mercury adsorption.


11:00 AM V9.7
Plasmon Resonance Tip Sensor for Drop Analysis. Marc Chaigneau¹, Karla Balaa¹, Minea Tiberiu² and Guy Louarn¹; ¹Institut des Matériaux Jean Rouxel (IMN), Nantes, France; ²Laboratoire de Physique des Gaz et Plasmas, Paris, France.

An original miniaturized fiber tip sensor based on the plasmon resonance is reported here. The fabrication process is inspired by our approach for probes manufacturing in scanning near-field optical microscope (SNOM). The etching method used, called substitute-sheath etching, allows for the production of optical fiber tips with optimal characteristics in a reproducible way. This improved one-step method strongly simplifies the usual processes, which requires parameters controlling, to produce three-dimensional probe tip. The sensitive area of the sensor is 400 µm length. We choose wavelength modulation to analyse the sensors response of a single solution drop. The plasmon resonance signal, that is sensitive to the refractive index environment of the metallic tip surface, is monitored by the light transmitted through the tip’s silver layer (collection mode). To test the capability of sensing, fiber optic sensors have been analyzed with several glycerol solutions of various concentrations that correspond to different refractive indexes (RI). The sensor configuration allows for the detection in volumes as small as one drop of solution (20 µl). The sensor responds successfully to refractive indexes in the range of 1.33-1.41 RI, with a sensitivity of 3.2×10-4 RI units. This response behavior is linear and covers a large region for sensing applications in aqueous environments. The deposition of a self assembled monolayer improves the stability of the sensor and increases its sensitivity by grafting selective molecules. The simplification of the experimental set up, the simplicity and reproducibility in the sensors manufacturing and the small volume of detection take an interest in biomedical applications.


11:15 AM V9.8
Engineering the Plasmonic Properties of Pd Nanostructures for SERS Detection Yujie Xiong, Younan Xia and Joseph M McLellan; Chemistry, University of Washington, Seattle, Washington.

Surface-enhanced Raman scattering (SERS) has been widely used to detect analytes at low concentrations. Previously most of the efforts were devoted to coinage metals (Ag, Au, and Cu) because their surface plasmon resonance peaks are located in the visible region. Palladium (Pd) is not a popular substrate for conventional SERS with visible or near-IR laser because the SPR bands of Pd nanoparticles are confined to the UV region. In this presentation, I will demonstrate how Pd nanostructures can serve as active substrates for conventional SERS detection by shifting their SPR bands to the visible region through shape-controlled synthesis. We have recently realized these opportunities by four different approaches: i) to increase the size of Pd nanocubes from 8 to 50 nm and shift the SPR peak from 225 to 390 nm; ii) to transform solid nanocubes of Pd into hollow nanocages and shift the SPR peak from 410 nm to 520 nm; iii) to grow Pd triangular and hexagonal nanoplates with SPR peaks around 520 nm; and iv) to synthesize Pd icosahedrons with SPR peak located at 390 nm. By engineering their SPR properties, we are able to substantially enhance their SERS activities. This talk will also compare the SERS activities with the positions of SPR bands and thus as a function of size, shape, and solidity. The intriguing application of Pd in nanocatalysis and its exceptional chemical sensitivity to hydrogen will make Pd-based SERS detection an attractive platform.


11:30 AM *V9.9
Layer Micro Patterning by Flame Deposition - Annealing. Sotiris E. Pratsinis, Department for Mechanical and Process Engineering, ETH Zurich, Zurich, Switzerland.

Tighter emission, security and health control regulations require sensors of higher sensitivity, stability and selectivity providing reliable output at different environments. This poses a challenge on the efficient manufacture of these materials as sensing particle properties such as size, composition, crystallinity and morphology need to be precisely controlled. Flame technology can readily produce SnO₂ and TiO₂ nanoparticles for sensing pollutant gases (1) and organics (2). Recently it was shown that it is possible to make highly sensitive gas sensors by directly depositing flame-made metal/ceramic nanoparticles onto sensing electrodes (3). That way, highly porous (98% porosity) sensing layers are formed allowing rapid detection of gases at rather low concentrations (below 1 ppm). This one step layer deposition method drastically simplifies sensor manufacture by bypassing the cumbersome wet chemistry steps employed today in solid-state sensor technology. Emphasis now is placed on deposition and adhesion of these flame-made nanoparticles on sensor substrates. More specifically, a wafer-level, CMOS-compatible, 2-step process for the in situ synthesis, deposition and annealing of highly sensitive, nanostructured sensing layers is explored. First, a flame spray pyrolysis (FSP) reactor is used to directly deposit SnO₂ - based nanostructured spider-web-like layers on macro- and micro-scale sensor substrates. In a second step, the layers are in-situ flame-annealed resulting in cauliflower-like layers of vastly improved particle cohesion and adhesion to the substrate which is highly desirable for further processing, while preserving layer uniformity, crystal phase and size. Microstructuring of these layers down to 100 x 100 μm² is explored by selected shadow masks in front of the nanoparticle-laden FSP hot jet close to the wafer surface. The electrical properties of the nanoparticle layers are tuned by multiple FSP deposition-annealing cycles that reduce layer resistance from 107 to 105 Ohm. The sensor performance is established for CO and ethanol (EtOH), so concentrations down to the low ppm level could be detected for both conventional-type and microsensors. 1. T. Sahm, L. Madler, A. Gurlo, N. Barsan, S.E. Pratsinis, U. Weimar, Flame spray synthesis of tin oxide nanoparticles for gas sensing, Sens. Actuators B, 2004, 98, 148-53. 2. A. Teleki, S.E. Pratsinis, K. Kalyanasundaram, P.I. Gouma, Sensing of organic vapors by flame-made TiO₂ nanoparticles, Sens. Actuators B, 2006, 119, 683-90. 3. L. Madler, A. Roessler, S.E. Pratsinis, T. Sahm, A. Gurlo, N. Barsan, U. Weimar, Direct formation of highly porous gas-sensing films by in-situ thermophoretic deposition of flame-made Pt/SnO₂ nanoparticles, Sens. Actuators B, 2006, 114, 283-95.