Vivek M. Prabhu National Institute of Standards and Technology
George Fytas University of Crete
Ali Dhinojwala The University of Akron
V1: Charged Brushes, Multilayers and Thin Films
Tuesday PM, April 18, 2006
Room 2000 (Moscone West)
9:30 AM - **V1.1
Doping Controls Dynamics in Polyelectrolyte Multilayers.
Joe Schlenoff 1 , Houssam Jomaa 1 , Jad Jaber 1 , Rana Jisr 1 Show Abstract
1 Chemistry and Biochemistry, Center for Materials Research and Technology, Florida State University, Tallahassee, Florida, United States
Polyelectrolyte multilayers (PEMUs) are a special case of polyelectrolyte complexes, where the components are held together by multiple ion pairing (“electrostatic bonding”) between oppositely charged repeat units. The interactions may be viewed as cooperative, since each ion pair contributes to a net intermolecular interaction energy (to a first approximation). Thus, even weak ion pairing leads to strong molecular association when many pair interactions are summed. As a result of these multiple interactions, complexed polyelectrolytes are essentially frozen in place. Any motion of individual segments is constrained by being coupled to the movement of other segments. It is possible, however, to enhance the degrees of freedom of a polyelectrolyte chain within a complex by breaking specific ion pair associations. This internal dissociation of ion pairing is caused by the addition of salt to the solution to which the multilayer is exposed. Salt ions swell the multilayer reversibly. In this talk, we will discuss polyelectrolyte dynamics on two levels: the first is the net movement of polyelectrolytes within the complex; the second deals with segmental motions, as revealed by dynamic mechanical studies.  We have followed polyelectrolyte interdiffusion by tracking morphological changes at the surface and by probing internal structural changes with neutron reflectometry. While multilayer components are, indeed, frozen in the absence of salt, in the presence of NaCl of sufficient concentration the polyelectrolytes move, albeit extremely slowly. Internal motion of polyelectrolytes was observed by interspersing layers of deuterated poly(styrene sulfonate) within a multilayer of poly(styrene sulfonate), PSS/poly(diallyldimethylammonium), PDADMA. Structural refinement using the neutron reflectograms provided time-resolved profiles of deuterated material within the multilayer. A diffusion model was fit to extract interdiffusion coefficients. Mechanical testing was performed on microcoupons of PEMUs peeled from Teflon substrates. Samples were deformed while exposed to baths containing salt NaCl of various concentrations. Static and dynamic deformation studies showed that PEMUs could be reversibly deformed as long as the strain was maintained below about 3%. Analysis of the shear modulus using classical statistical crosslinking theory showed that only a minority of ion pairing interactions yield actual crosslinks – rather, the bulk of the polyelectrolyte is associated ladder-like. PEMUs exist, in effect, as a network of ladders. The damping properties of complexed polyelectrolytes turned out to be exceptional, due to the wide range of internal modes for energy loss.
10:00 AM - V1.2
Ordering Behavior of Charged M13 viruses in Self-Assembled Viral Monolayer: From Molecule to Layer Control
Pil Yoo 1 , Ki Tae Nam 2 , Angela Belcher 2 3 , Paula Hammond 1 Show Abstract
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Biological Engineering Division, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
A study on the molecular property and dynamics of M13 virus during the process of electrostatically induced monolayer formation has been investigated. Self-assembled viral monolayer was prepared by adsorbing a negatively-charged M13 virus on a weakly charged polyelectrolytes multilayer support consisting of a cationic linear polyethyleneimine (LPEI) and anionic polyacrylic acid (PAA). Due to the interdiffusion phenomenon in underlying polyelectrolytes layer, macromolecular virus molecules are freely mobile on the top surface of LPEI/PAA multilayer. This mobility leads to the closely-packed two-dimensional monolayer assembly of viruses because of their repulsive characteristics as a liquid crystalline-like material. The resulting monolayer can be tuned for various assembly properties, such as packing density, directionality and ordering morphology by varying the pH of polyelectrolytes and virus solution. A change in magnitude of ionic linking between underlying polyelectrolytes determines the molecular rigidity and shape of individual M13 virus, comes from the protein interactions around virus body with environmental medium of polyelectrolyte molecules, and results in morphological difference during assembly process. On the other hand, a change in charge strength of M13 virus determines the total number of adsorbing viruses that can compensate the charged binding with underlying polyelectrolytes, which leads to the overall difference in assembly density. Temperature dependency of virus on assembly behavior was also investigated. The increased surface mobility of virus on polyelectrolytes at higher temperature induces much more ordered and less defects existing monolayer assembly. This study provides a general understanding to control the biomolecular self-assembly from individual molecular scale to collective layered scale. We also believe that it can suggest a basic and versatile tool for manipulating the properties of biomolecular monolayer and its applications in biomimetics or bio-inspired device fabrications.
10:15 AM - V1.3
Diffusion and Exchanges Processes in Heterostructured Polyelectrolyte Multilayers
Nicole Zacharia 1 , Paula Hammond 1 Show Abstract
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Layer by layer (LbL) has shown itself to be a very simple and versatile tool for the assembly of thin polyelectrolyte films. It is hoped that eventually more and more complex functionality will be allowed to be incorporated into these films. In these functional films it may be required to build complicated heterostructured from polyelectrolytes, and in these cases it is important to understand the morphology of these films. In certain cases, processes of macromolecular diffusion and exchange can destroy any stratification of the layers which might be desired. In this study, we examine the ability of polyethyline imine (PEI) to diffuse through a film of polyhexylviologen (PXV) and polyacrylic acid (PAA), and exchange with the short PXV chains. Diffusion processes in LbL films which are non-linearly growing have been previously examined, but our case is different in that it occurs in systems which grow linearly. We follow the growth of our multilayers using FTIR spectroscopy and confocal microscopy. Also, we demonstrate a method for preventing the diffusion and exchange from taking place by inserting crosslinked blocking layers. We demostrate over which parameters of pH the exchange takes place and propose explanations for our observations.
10:30 AM - **V1.4
Interaction of Polyelectrolyte Brushes with Small and Large ions.
Rupert Konradi 1 , Hyun-Kwan Yang 1 , Jurgen Ruhe 1 Show Abstract
1 Department of Microsystems Engineering, University of Freiburg, IMTEK, Freiburg Germany
11:30 AM - V1.5
Counterion–Dependent Wettability of Surfaces Modified with Cationic Polyelectrolyte Brushes.
Omar Azzaroni 1 , Andrew Brown 1 , Sergio Moya 2 , Wilhelm Huck 1 2 Show Abstract
1 Melville Laboratory for Polymer Synthesis, University of Cambridge, Cambridge United Kingdom, 2 The Nanoscience Centre, University of Cambridge, Cambridge United Kingdom
11:45 AM - V1.6
UCST Wetting Transitions of Polyzwitterionic BrushesDriven by Self-Association.
Andrew Brown 1 , Omar Azzaroni 1 , Wilhelm Huck 1 Show Abstract
1 Department of Chemistry, University of Cambridge, Cambridge United Kingdom
Chemical modification of solid substrates with zwitterionic functionalities has been the subject of intensive research work for many years. Experimentally, a reversible self–association is observed for certain polyzwitterionic hydrogels which display an upper critical solubility temperature (UCST), as a result of strong inter- and intra- molecular dipolar interactions leading to (reversible) self–association of the polymer chains. We have synthesized homogeneous and patterned brushes of [2–(methacryloyloxy)ethyl]–dimethyl–(3–sulfopropyl) ammonium hydroxide (MEDSAH), via surface-initiated, atom transfer radical polymerization (ATRP), and shown that the bulk or solution behaviour of this sulfobetaine has its counterpart in the surface domain through the thickness, and temperature–dependent characteristics of the brush–like layer. This dependence is evidenced through a pronounced transition in the wetting characteristics that is related to the polyzwitterionic brush forming a completely collapsed self–associated state, which has a significant impact on the wetting characteristics. After passing through a hydrophilic, non-associated regime with θAW ~12°, a self–associated regime begins to develop with hydrophobic surface characteristics reaching θAW ~75°. This sharp difference in the interaction between the water and the two states was also observed in the swelling behaviour studied by AFM experiments performed in water. Finally, we have observed that the self–associated state can be reversed by increasing the temperature, leading to a hydrophobic–to–hydrophilic switch in close resemblance to the UCST characteristics observed for the same polyzwitterion in solution. The magnitude of the effect (ΔθAW ~20–25°) is similar to the well-known polyacrylamide–based brushes and hydrogels, but with an inverse thermoresponsive behaviour. Consequently, these studies are a crucial step toward the translation of polyzwitterionic solution behavior to surfaces, in order to exploit their rich behaviour in the development of new smart responsive coatings and in designing more complex microfluidic device layouts.
12:00 PM - **V1.7
Surface Modification by Charge-Regulating Polyelectrolyte Layers: Effect on Particle Adsorption.
Nily Dan 1 Show Abstract
1 Chemical and Biological, Drexel University, Philadelphia, Pennsylvania, United States
We investigate the electrostatic interactions between charge-regulating polyeletrolyte layers and adsorbing particles (used as a model for protein or cellular adsorption). We find that charge regulation and the presence of an ion-penetrable layer leads to several surprising trends. Specifically, we conclude that electrostatic interactions, although supposedly non-selective, can in fact be used to selectively adsorb specific protein or cell types onto substrates.
12:30 PM - **V1.8
Tuning Soft, Hydrated Interfaces Composed of Tethered Polymer Layers with Multi-Valent, Ionic Interactions
Matthew Tirrell 1 , Akira Ishikubo 1 , Feng Li 1 Show Abstract
1 Chemical Engineering and Materials, UC Santa Barbara, Santa Barbara, California, United States
End-tethered polyelectrolyte layers (“brushes”) shrink or swell monotonically in response to addition or diminution of mono-valent salt, which also produces corresponding monotonic changes in the range of the repulsive normal forces by or between two such brushes. High swelling and very low frictional forces have been reported under low salt concentrations. In this talk, a new pattern of behavior is demonstrated via surface force measurement on anionic polyelectrolyte brushes in the presence of multi-valent ionic interactions, introduced via tri-valent aluminum cations (Al3+) or aggregates of cationic surfactants. Very low concentrations of added Al3+ or surfactant produce much stronger shrinkage of the brush than does mono-valent salt. More strikingly, the normal forces become strongly attractive under these circumstances. Multi-valent interactions enable tuning of polyelectrolyte brush structure and properties over a very wide range, from compact, stiff and sticky to swollen, soft and repulsive.
V2: Polyelectrolyte Thin Films: Swelling and Dissolution
Tuesday PM, April 18, 2006
Room 2000 (Moscone West)
2:30 PM - **V2.1
Kinetics of Ionization and Photoresist Dissolution
William Hinsberg 1 , Frances Houle 1 Show Abstract
1 , IBM Almaden Research Center, San Jose, California, United States
Modern photoresists are designed to undergo a localized change in polymer properties triggered by spatially directed irradiation of a thin film. Dissolution of polymer chains during a final image development step is the transform that links the detailed form of the final relief image to the compositional latent image formed through irradiation. The dissolution of exposed regions of polymeric resists in aqueous base to form a pattern is a complex reactive process, and is usually described only empirically. Using experimental characterization of the polymer dissolution process by optical and gravimetric analysis, combined with detailed kinetics simulations to predict time-dependent resist film masses and layer thicknesses, we examine how resist imaging characteristics can be linked to their dissolution behavior. The reaction-diffusion model explicitly describes deprotonation, reneutralization and diffusion processes and is based on a simple reaction scheme that assumes a critical level of ionization is required for a polymer chain to move from the film into solution. We will show that many experimental observables are readily explained within this framework.
3:00 PM - V2.2
Probing Solid-liquid Interface Dynamics by Evanescent Wave Dynamic Light Scattering.
Benoit Loppinet 1 , Vassiliki Michailidou 1 , Fytas George 1 , Ruehe Juergen 2 Show Abstract
1 , IESL-FORTH, HERAKLIO, Crete, Greece, 2 , IMTEK, Freiburg Germany
3:15 PM - V2.3
Dissolution Fundamentals of 193-nm Methacrylate Based Photoresists
Ashwin Rao 1 , Shuhui Kang 1 , Bryan Vogt 1 , Vivek Prabhu 1 , Eric Lin 1 , Wen-li Wu 1 , Karen Turnquest 2 , William Hinsberg 3 Show Abstract
1 Polymers Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 , Sematech, Austin, Texas, United States, 3 Almaden Research Center, IBM, San Jose, California, United States
The dissolution of partially deprotected chemically amplified photoresists is the final step in printing lithographic features. Since this process step can be tuned independently from the design of the photoresist chemistry, fundamental measurements of the dissolution behavior of photoresists may provide needed insights towards improving line-edge roughness. We have studied the dissolution behavior of a model 193-nm photoresist, poly (methyladamantyl methacrylate), as a function of deprotection extent and developer strength. The kinetics of the dissolution process is followed using the quartz crystal microbalance technique, while the steady state swelling behavior is studied using light interferometry. These photoresist films exhibit strong swelling without dissolution over a narrow-range of deprotection levels. At larger extents of deprotection, we observe a combination of swelling with dissolution. Additionally, we find a maximum degree of film swelling with tetramethylammonium hydroxide developer concentration. If photoresist swelling and dissolution strongly affect CD control or LER, these studies provide the insight needed to better design developer materials and strategies.
3:30 PM - V2.4
Swelling/deswelling Behavior of Polyelectrolyte Multilayers in Confined Geometry: pH-induced Gating of Track-etched Polycarbonate Membranes.
Daeyeon Lee 1 , Adam Nolte 2 , Allison Kunz 2 , Michael Rubner 2 , Robert Cohen 1 Show Abstract
1 Chemical Engineering Department, MIT, Cambridge, Massachusetts, United States, 2 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Polyelectrolyte multilayers prepared via layer-by-layer assembly of a weak polycation (poly(allylamine hydrochloride) (PAH)) and a strong polyanion (poly(styrene sulfonate) (PSS)) at a high pH condition (pH > 9.0) show discontinuous swelling/deswelling transitions as a function of solution pH. These reversible transitions are induced by discontinuous changes in the degree of ionization of PAH. In this study, the multilayer thin films comprised of PAH and PSS were assembled within the pores of track-etched polycarbonate membranes (400 or 800 nm in diameter). The swelling/deswelling behaviors of the multilayers in confined geometry (cylindrical pores) were studied by measuring changes in the flux of pH adjusted water through the multilayer-modified membranes. Flux as a function of solution pH exhibited a large hysteresis loop similar to the volume changes observed in previous studies on planar supports. However, the degree of swelling of multilayers in the cylindrical pores is smaller compared to the swelling of the same multilayer system on a planar geometry. We also demonstrate that the deposition of multilayers is an effective means to create pH-responsive membranes. By changing solution pH over the range from 2 to 11, more than two orders of magnitude changes in flux could be achieved. These multilayer-modified microporous membranes can be utilized to filter macromolecules based on a size-exclusion principle and also can potentially be used to separate small ions at a high flux rate by utilizing the overlap of electrical double layer within constricted pores.
3:45 PM - **V2.5
Polyelectrolytes at Interfaces.
M. Muthukumar 1 Show Abstract
1 , University of Massachusetts-Amherst, Amherst, Massachusetts, United States
Using theoretical considerations, we will discuss (1) adsorption of single chains onto patternd surfaces and brushes, and (2) stability of interfaces of polyelectrolyte films upon exposure to salty water. For the first problem, criteria for adsorption are obtained. For the second problem, laws of polyelectrolyte phase behavior and dissolution kinetics of thin polyelectrolyte films are derived. The implications of our results in viral packaging and lithography will be discussed.
V3: Conformation and Dynamics of Single Molecules
Tuesday PM, April 18, 2006
Room 2000 (Moscone West)
4:30 PM - **V3.1
Dynamics of a Single Enzyme Molecule at the Liquid-Solid Interface
Haw Yang 1 2 Show Abstract
1 Chemistry, UC Berkeley, Berkeley, California, United States, 2 Physical Biosciences, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Biological macromolecules are dynamic entities that wobble and tumble while performing their functions. The time scale of such fluctuations may span many decades from picoseconds (10-12 s) to seconds. Especially important are those conformational changes that occur on the catalytically important time scale, from millisecond (10-3 s) to second. Yet, these structural movements are difficult to study because molecular motions are not synchronized on these time scales. Fluorescence single-molecule spectroscopy is a uniquely powerful approach that allows one to directly visualize the dynamical aspects between its 3D structure and the function of an enzyme. Since it focuses on one molecule at a time, it is no longer necessary to synchronize the motions of an ensemble of molecules. The distribution of conformational states and the structural changes that lead to reactive events can in principle be directly observed and characterized. These observations, however, are near the limits of optical detection such that raw experimental data are inundated with Poissonian photon counting noise. It is thus challenging to elicit quantitative dynamical information from these noisy trajectories. We have developed a suite of new approaches, both theoretically and experimentally, to address this issue. These statistically robust methods extract information from photon arrival time stream one photon at a time and reveal unprecedented details about the dynamics of a working enzyme. We will discuss these advances towards high-resolution, time-dependent single-molecule spectroscopy, and their application to understanding the dynamics of various biomolecules, including the adenylate kinase from Escherichia coli.
5:00 PM - V3.2
Conformations of Single Flexible Polyelectrolyte Molecules at Solid-Liquid Interface: High Resolution AFM Visualization.
Yuri Roiter 1 , Sergiy Minko 1 Show Abstract
1 Department of Chemistry, Clarkson University, Potsdam, New York, United States
We report on the direct study of conformations of the protonated adsorbed poly(2-vinylpyridine) (P2VP) and poly(methacryloyloxyethyl dimethylbenzylammonium chloride) (PMB) molecules on the mica surface. The single molecules were adsorbed on the mica and visualized in situ under aqueous solutions at different pH values and ionic strength. We have developed the AFM experiments for the direct study of "thin" (from about 0.4 nm thick) polyelectrolyte molecules at the interface under liquid media. We have used these experiments to quantify the coil-to-globule transition in terms of root mean square end-to-end distance and root mean square gyration radius of the polyelectrolyte molecules, when the changes of the dimensions were induced by changes of pH and ionic strength of the solutions. At low pH values of aqueous solutions P2VP chains were adsorbed in the conformation of 2D warm-like extended coils. We observed the formation of Z-compressed globules of the P2VP molecules at pH > 3.9. Based on the quantitative analysis of the experimental dimensions of the adsorbed polyelectrolyte molecules we suggest a hypothetic two-level organization of the adsorbed charged polymers. The first level is a "wavy" structure formed due to the strong van der Waals interaction with the substrate. The second level is likely a self-avoiding random walk coil. The structure of the adsorbed layers depends on the charge of the substrate. On the positively charged mica the positively charged P2VP chains avoid contacts with the substrate. They tend to adsorb on the top of the adsorbed earlier P2VP chains rather than onto unoccupied areas of the mica substrate. The P2VP and PMB molecules were visualized as flat partially ordered pancake-like 2D globules at the increased ionic strength. We speculate that this conformation is strongly affected by a "bridging" effect of counterions.Most of the reported in literature AFM and SEM studies of relatively small synthetic polyelectrolyte molecules were carried out under air atmosphere. A few reports described the AFM under-liquid studies where the images resolve no fine conformational details of the adsorbed chains of polyelectrolyte molecules. The AFM images of giant polyelectrolytes such as DNA were successfully used for the analysis of the conformations in situ under aqueous solutions. In the presented here experiments we demonstrate new interesting opportunities for study of thin flexible polyelectrolytes at solid-liquid interface using the in situ AFM method.
5:15 PM - V3.3
Protein-surface Interactions Investigated with Solid State NMR, Neutron Reflectivity and Computational Modeling.
Wendy Shaw 1 , Susan Kreuger 2 , Kim Ferris 1 , Ursula Perez-Salas 2 3 , Vitalii Silin 2 , Duncan McGillivray 2 4 Show Abstract
1 , Pacific Northwest National Labs, Richland, Washington, United States, 2 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 3 , University of California at Irvine, Irvine, California, United States, 4 Department of Biophysics, Johns Hopkins University , Baltimore, Maryland, United States
Biomineralization proteins are exquisite modifiers of inorganic minerals, with examples including bones and teeth, however very little is understood about how these proteins interact with crystals to provide the resulting control. Here we investigated an amelogenin, LRAP, to understand the orientation of the protein on the hydroxyapatite (HAP) surface, the dynamics of the surface immobilized protein and amino acids important in interacting with HAP. Amelogenin consists of 90% of the protein present during the formation of the unusually long and highly ordered enamel crystals and is found to be critical in proper enamel development. There is indirect evidence a specific interaction between the C-terminus of amelogenin and the crystal lattice exists, but no direct measurements to indicate how the protein is interacting with the inorganic crystal. Solid state NMR and neutron reflectivity are complementary techniques which can provide insight into the protein-crystal interface, under biologically relevant conditions. Using solid state NMR and NR, experimental data will be presented that demonstrate that the C-terminus of LRAP is close enough to the surface of HAP to influence the resulting crystal structure. Modeling results of the LRAP-HAP interface will also be presented. In addition to providing significant molecular level insight into enamel formation, this work displays the ability of these techniques to quantitate macromolecule/mineral interfacial interactions. This work was funded by the NIDCR institute of NIH. PNNL is operated by Battelle Memorial Institute for the U.S. Department of Energy.
5:30 PM - V3.4
WITHDRAWN 4/12/06 Dynamics of ssDNA Monolayers on Gold Monitored by Electrochemical Impedance Spectroscopy.
Joel Rivera-Gandia 1 , Carlos Cabrera 1 Show Abstract
1 Chemistry Department, University of Puerto Rico, San Juan, Puerto Rico, United States
Vivek M. Prabhu National Institute of Standards and Technology
George Fytas University of Crete
Ali Dhinojwala The University of Akron
V4: Microarray and Microfluidics Fundamentals
Wednesday AM, April 19, 2006
Room 2000 (Moscone West)
9:30 AM - **V4.1
Properties and Applications of DNA Monolayers.
Rastislav Levicky 1 Show Abstract
1 Chemical Engineering, Columbia University, New York, New York, United States
We investigate DNA monolayers on metal and dielectric supports. Chains ranging in size from oligonucleotides to gene-sized polymers have been site-specifically attached without detectable side reactions in an end-tethered, "polymer brush" geometry. On metal supports, polythiol-mediated anchoring can be used to provide highly permanent immobilization of the nucleic acid. X-ray photoelectron spectroscopy (XPS) and electrochemical methods have been applied to investigate the charging behavior, counterion partitioning, and organization of DNA monolayers on metal supports. The interfacial capacitance of end-tethered DNA films has been interpreted within a polyelectrolyte brush model. Retention of counterions by the DNA brush manifests as lowered susceptibility of the interfacial capacitance to external salt conditions, and the data indicate a reorganization of the monolayer with changes in ionic strength and strand coverage. Diagnostic applications are being pursued through development of near-field imaging methods and of active microelectronic substrates that integrate signal detection and processing functionality "on-chip." Near-field measurements offer a label-free technique with a sensitivity comparable to that of fluorescence-based systems currently in widespread use. Microelectronic biochips replace costly macroscopic instrumentation by integration of equivalent function within the solid support, using affordable CMOS microfabrication.
10:00 AM - V4.2
Polyelectrolyte Behavior in Monolayers of ssDNA Immobilized on Gold.
D. Petrovykh 1 2 , A. Opdahl 3 , H. Kimura-Suda 3 , M. Tarlov 3 , L. Whitman 1 Show Abstract
1 , Naval Research Laboratory, Washington, District of Columbia, United States, 2 Department of Physics, University of Maryland, College Park, Maryland, United States, 3 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
10:15 AM - V4.3
Surface Reactions Of Dna And Proteins On Functionalized Thin Film Surfaces Controlled By The Application Of A Single Voltage Pulse.
Joao Conde 1 3 , Ricardo Cabeca 1 2 , Ana Perreira 1 2 , Ana Roque 1 2 , Ana Fixe 1 2 , Duarte Prazeres 2 3 , Virginia Chu 1 Show Abstract
1 , INESC Microsistemas e Nanotecnologias, Lisbon Portugal, 3 Dept. of Chemical and Biological Engineering, Instituto Superior Tecnico, Lisboa Portugal, 2 Center of Biological & Chemical Engineering, Instituto Superior Tecnico, Lisbon Portugal
The widespread application of biochips in genetic and proteomic analysis, pathogen identification, and disease diagnostics, requires rapid, accurate and inexpensive fabrication and simple, reliable diagnostics. The integration of electronics with biology has great potential in both these areas. Previously, we reported the use of single square voltage pulses to enhance by 7 to 9 orders of magnitude the rate of covalent immobilization and the rate of hybridization of single stranded DNA probes on a chemically functionalized thin film surface (silicon dioxide) [1-2]. The functionalization of the surface was performed via silanization with amino propyl triethoxy silane (APTES) and subsequent addition of a cross-linking molecule (sulfo-EMCS or glutaraldehyde). The voltage pulse was applied to integrated metal electrodes (voltage and ground lines) incorporated below the functionalized thin film surface. The electric field-assisted DNA immobilization and hybridization occurs in the microsecond time scale, far faster than the 2 hrs needed for immobilization and hybridization to proceed to completion without the electric field. The effect of the voltage pulse voltage, pulse duration, and pulse shape on the DNA immobilization and hybridization density will be presented. The potential extension of this technique to control the immobilization and the reactivity of model proteins (E-GFP and antibody/antigen complexes) will also be presented. We will also describe a model of the effect of a fast voltage pulse on the charged biomolecule reactivity in the biochip, based upon field-induced de-stabilization of a pre-adsorbed biomolecular monolayer. The influence of the sign and density of the electric charges present in the biomolecule, as well as the influence of the sign of the surface charges, on the voltage pulse-assisted reactions will be discussed.These results suggest that cleanroom microtechnologies and electronic addressing of pixel elements can be used in both the production of high-density biochips (by controlling the kinetics of the immobilization of biomolecules) and in the analysis of the microarray data by significantly speeding up biomolecular recognition reactions.  “Immobilization and hybridization by single sub-millisecond electric field pulses, for pixel-addressed DNA microarrays”, F. Fixe, H.M. Branz, N. Louro, V. Chu, D.M.F. Prazeres, J.P. Conde, Biosensors and Bioelectronics 19, 1591 (2004). “Electric-field assisted immobilization and hybridisation of DNA oligomers on thin-film microchips”, F. Fixe, H.M. Branz, N. Louro, V. Chu, D.M.F. Prazeres and J.P. Conde, Nanotechnology 16, 2061(2005).
10:30 AM - V4.4
Protein Micro-Array Technology Based on Functionalized Core-Shell Nanoparticles
Guenter Tovar 1 2 , Kirsten Borchers 2 , Achim Weber 1 , Herwig Brunner 1 2 Show Abstract
1 Biomimetic Surfaces, Fraunhofer IGB, Stuttgart Germany, 2 Institute for Interfacial Engineering, University of Stuttgart, Stuttgart Germany
In our approach to a flexible surface-chemistry for protein-immobilization to micro-arrays we use core-shell nanoparticles as carriers for a variety of capture-molecules. Silica nanospheres are equipped with an organic shell using functional silanes and bioconjugate chemistry to couple specific capture proteins such as antibodies, streptavidin etc. 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 surfaces activated by polyelectrolyte deposition in a micro-structured way by combination of a broad range of top-down structuring methods.Nanoparticles display a very large surface and thus layers of functional nanoparticles adsorbed to a solid substrate display an increased amount of receptor sites per area. Hence micro-structured nanoparticle layers form highly sensitive sensor surfaces for application in protein biochip technology.We will present results concerning the maintainance of protein function on nanoparticulate chip-surfaces, the dynamic range of nanoparticle-chips and chip-readout by fluorescence-detection or MALDI-mass-spectrometry.  Schiestel, T., Brunner, H., Tovar, G.E.M.; J. Nanosci. Nanotechn. 4 2004 1-8. Tovar, G.E.M., Schiestel, T., Hoffmann, C., Schmucker, J.; Bioforum Intl. 5 2001 235. A. Weber, S. Knecht, H. Brunner, G. E. M. Tovar, Engineering in Life Sciences 4 2004 93-97. G. E. M. Tovar, A. Weber, Dekker Ency. Nanosci. Nanotechnol. 1 2004 277-286. A. Weber, K. Borchers, G. E. M. Tovar, transkript Laborwelt 4 2003 20-21. K. Borchers, A. Weber, H. Brunner, G. E. M. Tovar;. Anal. Bioanal. Chem., in press.
10:45 AM - V4.5
Virus Modified Electrode
Li-Mei Yang 1 , Phillip Tam 1 , Ben Murray 2 , Gregory Weiss 1 , Reginald Penner 1 Show Abstract
1 Chemistry, University of California, Irvine, Irvine, California, United States, 2 Chemistry, KLA Tencor, San Jose, California, United States
The development of label-free biosensors for key biomolecules is an objective that is shared by many research groups worldwide. We present an approach involving the electrochemical detection of biomolecules binding to electrode surfaces on which an engineered bacteriophage, M13, has been covalently attached. This bacteriophage has - on its surface - polypeptide receptors that form the basis for molecular recognition. These phage particles are prepared using the techniques of phage display.We describe the preparation of the biosensor surface, the optimization of the electrochemical impedance measurement, and the results of our first experiments that involve the detection of antibodies that are recognized and bound by the immobilized phage particles, and “control” antibodies that are not recognized. The response of this biosensor to the prostate cancer marker, PMSA, is also reported. In all cases, the observed impedance responses are “benchmarked” against the response of a quartz crystal microbalance, on which the biosensor is constructed.
11:30 AM - V4.6
Spatial and Temporal Control of Actin Filament Polymerization using Nanoscale Electrodes
Ian Wong 1 , Nicholas Melosh 1 Show Abstract
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
The self-organization of negatively charged G-actin protein monomers into F-actin filaments and higher order structures is essential for the development and motility of eukaryotic cells. These dynamic processes are regulated spatially and temporally in vivo by various actin-binding proteins (ABP) and the concentration of free monomers. However, it is difficult to achieve similar dynamic control for in vitro systems, where F-actin polymerization is initiated by increasing the bulk concentrations of cations in solution up to physiological conditions. We demonstrate an integrated system of nanoscale electrodes that achieves spatial and temporal control of F-actin polymerization by locally concentrating cations in response to some applied AC voltage, thus screening the electrostatic repulsion between monomers. This represents an initial proof-of-concept for the electronic regulation of protein structure and function via ion concentration. At low frequencies, divalent cations and charged G-actin monomers are alternately concentrated at the electrode surface, promoting localized polymerization. This phenomenon is further enhanced at low frequencies due to electro-osmotic flow fields. At higher frequencies, F-actin filaments can be aligned and manipulated using dielectrophoretic forces. Such dynamic control over polymerization and spatial manipulation allows controlled assembly and disassembly of complex higher-order nanostructures. For example, in combination with actin-binding proteins and inorganic nanoparticles, it may be possible to functionalize hybrid biopolymer-inorganic analogs of linear and branched nanowires. Furthermore, single F-actin filament polymerization and control is relevant for controlling actin-myosin “molecular shuttles.”
11:45 AM - V4.7
Imaging Ellipsometry: Illuminating the Solid-liquid Interface.
Martin Laging 1 , Dirk Hoenig 2 Show Abstract
1 , Accurion Inc., Menlo Park, California, United States, 2 , Nanofilm Technologie GmbH, Goettingen Germany
Ellipsometry has proven to be a very versatile and powerful tool to investigate thin films at solid-air interfaces for a long time. In a non-destructive way, the properties of thin films (as thicknesses, refractive indices, extinction coefficients, roughness, mixtures of materials) can be determined. However, on structured samples as e.g. microarrays the conventional approach of ellipsometric measurement leaves you in the dark: A poor lateral resolution of the classical instruments does not allow visualization of the surface pattern or to independently measure multiple channels at the same time. Here, imaging ellipsometry comes into play. Using specifically designed flow cells and geometries it provides a direct visual access to the surface morphology at the solid-liquid (and solid-air) interface. At the same time it allows to monitor surface reactions in a spatially and time-resolved way, thus enabling multi-channel real-time binding kinetics. By this way, a method so far mainly used for solid state physics applications now finds its way into the (bio)chemistry labs. In this paper we present recent publications and yet unpublished applications (ranging from thickness mapping of micropatterned lipid bilayers, binding kinetics on protein arrays and imaging SPR, to studies of polymer films, e.g. the electrochemical deposition of polymers on metal surfaces) to demonstrate the potential and the benefits of imaging ellipsometry.
12:00 PM - V4.8
Impact of the Nonionic Surfactant Pluronic F127 on the Performance of a Polymeric Microfluidic Pre-Concentrator and Particle Sorting Device.
Blake Simmons 1 , Thomas Wallow 1 , Karen Krafcik 1 , Gregory McGraw 1 , Rafael Davalos 1 , Eric Cummings 2 , Gregory Fiechtner 2 Show Abstract
1 Nanoscale Science and Technology Department, Sandia National Laboratories, Livermore, California, United States, 2 Microfluidics Department, Sandia National Laboratories, Livermore, California, United States
We have previously reported on the use of insulator-based dielectrophoresis (iDEP) for the selective separation and concentration of biological particles and pathogens in water. We have found that the applied DC field required to trap these particles depends on particle size, shape, and the zeta potential of the material utilized to form the device. In order to improve device performance, and decrease the power required for optimal performance, it is necessary to adjust one (or several) of these parameters. Surfactants are known to adsorb onto polymeric surfaces in a dynamic fashion, and have been utilized extensively to modify device performance in such related fields as capillary electrophoresis and micellar electrokinentic chromatography. We present here the effect of the nonionic block copolymer surfactant, Pluronic F127, on the applied field strengths required to achieve effective isolation and trapping of polystyrene beads. The microfluidic devices are made entirely of a thermoplastic cyclic olefin copolymer, Zeonor. We have monitored the adsorption of the surfactant at the solid-liquid interface of the polymer through quartz crystal microbalance studies. We have correlated this data to the observed changes in the applied fields necessary for optimal device performance and have developed a proposed mechanism of interaction for this system. These results indicate that the presence of the surfactant adsorbed onto the polymer surface greatly lowers the applied field magnitude necessary to achieve particle separation and concentration.
12:15 PM - V4.9
Study of Molecular Transport in Nanofluidic Channels by Integrated Multiple Internal Reflection Infrared Waveguide.
Youn-Jin Oh 1 , Thomas Gamble 1 , Anthony Garcia 1 , Alexander Neumann 2 , Chan-Hwa Chung 1 , Dimiter Petsev 1 , Cornelius Ivory 3 , Steven Brueck 2 , Gabriel Lopez 1 , Sang Han 1 2 Show Abstract
1 Chemical & Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 2 Center for High Technology Materials, University of New Mexico, Albuquerque, New Mexico, United States, 3 Chemical Engineering, Washington State University, Pullman, Washington, United States
We have studied the flow control of molecules in nanofluidic channels with an isolated gate in a configuration that is analogous to field effect transistors (FETs). Various types of nanochannel structures are fabricated and tested to improve molecular transport. We have also successfully integrated nanofluidic channels into multiple-internal-reflection (MIR) infrared waveguides for the purpose of biomolecular separation and detection by FTIR spectroscopy. We have discovered that the biomolecules and the electrolyte solution can be probed by the MIR waveguide, provided that the channel width is substantially less than the IR wavelength. We demonstrate that the channels whose width is on the order of the Debye screen length of electrolyte solution as well as the dimension of biomolecules impart unique physical constraints on their transport.The velocity of dye molecules and their flow direction are successfully controlled by adapting an isolated gate under nanochannels in our experiments. We also report that the leakage current that typically flows through thin thermal SiO2 surrounding the channels can be reduced by a number of means, including the insertion of a Si3N4 layer between thermal SiO2 and the Si channel walls. Alexa 488 and Rhodamine B, which have different charges depending on the pH of buffer solution, are used as test molecules in our experiments to characterize their flow characteristics as a function of pH, using the MIR-FTIR spectroscopy as well as scanning laser confocal fluorescence microscopy. We have particularly monitored the surface adsorption and desorption of charged dye molecules on the walls of nanochannels during the "gated" flow control. The result shows that the surface processes can be monitored in situ during the transport and flow control of molecules.
12:30 PM - V4.10
X-ray Reflectivity and Fluorescence Microscopy on Solid Supported Membranes: Structure-function Relations.
Christian Reich 1 , Joachim Raedler 1 , Bert Nickel 1 Show Abstract
1 Dep.Physik & CeNS, Ludwig-Maximilians-Universitaet, Muenchen Germany
We have designed a microfluidic setup which allows for preparing and studying biological interfaces by x-ray reflectivity and fluorescence microscopy [C. Reich et al, Rev.Sci.Inst.76, 095103 (2005)]. This experimental approach allows us to study structure(membrane thickness, packing density) and function (e.g. diffusion, binding interactions) in one setup. First experiments have been performed on lipid bilayers supported by silicon oxide, by a thermoplastic material [M. Hochrein et al, Langmuir, in press], and by a poly-electrolyte coating. Present experiments aim on characterizing lipid-protein interactions and lipid-cholesterol mixtures.
V5: Colloid and Nanoparticle Synthesis and Assembly
Wednesday PM, April 19, 2006
Room 2000 (Moscone West)
2:30 PM - **V5.1
Segregation of Polymer Materials and Nanoparticles to Interfaces.
Todd Emrick 1 Show Abstract
1 Polymer Science & Engineering, University of Massachusetts, Amherst, Massachusetts, United States
The synthesis and interfacial segregation of polymer materials and nanoparticles will be described. Graft copolymers have been tailored for interfacial segregation and interaction with biomolecules, through control over the solubility properties and charge of the polymers by tailoring the grafted chains. Highly tailored novel polyelectrolytes can be prepared using this graft copolymer motif. Moreover, nanoparticles have been functionalized with with ligands that drive their interfacial activity, such that well-defined and unique materials can be prepared using only techniques of self-assembly.
3:00 PM - V5.2
Virus-Mimetic DNA Encapsulation Using Novel Polyelectrolyte Triblock Copolymers.
You-Yeon Won 1 , Rahul Sharma 1 Show Abstract
1 School of Chemical Engineering, Purdue University, West Lafayette, Indiana, United States
3:15 PM - V5.3
Hollow Shell Structure of MoS2 Prepared Inside the Viral Protein cage of Cowpea Chlorotic Mottle Virus as Determined by Through Focal Series Reconstruction HRTEM.
Mark Allen 1 2 , ChengYu Song 3 , Christian Kisielowski 3 , Andrew Minor 3 , Mark Young 1 4 , Trevor Douglas 1 2 Show Abstract
1 Chemistry and Biochemistry, Montana State University, Bozeman, Montana, United States, 2 Center for BioInspired Nanomaterials, Montana State University, Bozeman, Montana, United States, 3 Department of Plant Sciences, Montana State University, Bozeman, Montana, United States, 4 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Biological molecules often demonstrate a high degree of control over the formation of inorganic materials. Supramolecular protein assemblies have been used by biology and are studied for their properties for size constrained materials synthesis. Ferritin, viruses, and ferritin like proteins have been used for the synthesis of a wide range of materials including metal oxides and polyoxometallates. The spherical plant virus, Cowpea chlorotic mottle virus (CCMV), is a viral protein cage that assembles from 180 identical subunits. These self assembled 28 nm protein cages have electrostatically distinct interior and exterior environments making them ideal reaction vessels for material synthesis. CCMV has also been manipulated both genetically and chemically in order to make the assembled viral capsid stable to a wide range of conditions. This presentation will focus on the synthesis and characterization of a shell like structure of MoS2 prepared inside the 20-24 nm cavity of the CCMV protein cage. By incubating the CCMV protein cage with a precursor solution of MoO4- in the presence of ammonia at pH 7 then upon lowering the pH to 4.5 an amorphous polyoxomolybdate is prepared that can be transformed to MoS2 by placing the solution in an atmosphere of H2S gas. Once the MoS2 mineral is prepared high resolution electron microscopy can be done in order to gain information about the crystalline material prepared inside the virus. Using a Philips 300FEG/UT microscope at the national center for electron microscopy it was possible to characterize the MoS2 material to nearly one Å resolution using a technique of through focal series reconstruction. Upon analysis the MoS2 prepared inside the virus has a novel shell structure that is defined by the interior dimensions of the protein cage. This shell of MoS2 appears to be hollow as determined by lattice imaging and reconstructions. This technique in conjunction with analytical electron microscopy will probe the protein/material interface.
4:00 PM - **V5.4
Complexation and Aggregation of Charged Macromolecules
Kurt Kremer 1 , Christian Holm 1 2 Show Abstract
1 , Max-Planck Institute for Polymer Research, Mainz Germany, 2 , Frankfurt Institute of Advanced Studies (FIAS), Frankfurt Germany
Using extensive Molecular Dynamics simulations we study thebehavior of very rigid polyelectrolytes with hydrophobic side chains, that are known to form cylindrical micelles in aqueous solution. We investigate the stability of such micelles with respect to hydrophobicity, Coulomb interaction, and micellar size. We show that for the parameter range relevant for poly-para-phenylene sulfonates (PPP) one finds a stable finite micellar size close to the experimental parameter region. We also point out that our model has some similarities to DNA solutions with added condensing agents, hinting to the possibility that the size of DNA aggregates is under certain circumstances thermodynamically limited. Beyond that the interaction of charged chains with charged colloids as well as first studies on hydrogels are presented. To improve the comparison of simple generic models with experiments, new simulations are performed where the implicite water is replaced by explicite water for certain limiting cases.Limbach HJ, Holm C, Kremer K, Macrom. Chem. and Phys. 206, 77 (2005) Messina R, Holm C, Kremer K, J. Pol. Sc. Part B, 42, 3557 (2004) Mann BA, Holm C, Kremer K JCP, 122 Art. No. 154903 (2005)
4:30 PM - V5.5
Assembly of DNA Coated Colloids Directed by the Hybridization of Long and Flexible DNA Molecules.
Tatiana Schmatko 1 4 , Erika Eiser 2 , Daan Frenkel 1 , Wilson Poon 3 1 4 Show Abstract
1 , FOM institute for Atomic and Molecular Physics (AMOLF), Amsterdam Netherlands, 4 COSMIC (Collaborative Optical Spectroscopy, Manipulation and Imaging Centre), University of Edinburgh, Edinburgh United Kingdom, 2 Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Amsterdam Netherlands, 3 School of Physics, University of Edinburgh, Edinburgh United Kingdom
Over the past ten years, researchers have focused their interest on building new types of nanomaterials based on DNA assemblies, involving the specific recognition of two complementary strands. DNA coated coloids have the ability to form reversible networks[1,2], (via the melting of the DNA double helix) with different degree of order. A recent theoretical work  shows that very long flexible DNA, with a polymer like behaviour, would allow the formation of numerous phases that are forbidden for short DNA-colloids systems. This paper directly inspired our work. We present the first experimental study of self assembly in colloids coated by 16 mm long double-stranded phage lambda DNA. We prepare two populations of particles in which the tethered DNA molecules have complementary, 12bp ‘sticky ends’. Confocal imaging of a mixture of these particles show that temperature mediates the formation of a cluster phase. Surprisingly the inter-colloidal distance within clusters is very small, leaving no room for the DNA chain. Comparing our results with simulations and calculations, we show that the DNA is expelled out of the cluster by an entropic mechanism. This DNA-induced attraction that can be modulated with the parameters of the system offering then new routes to tune the distance between particles. . Mirkin, C. A., Letsinger, R. L., Mucic, R. C. & Storhoff, J. J. A DNA-based method for rationally assembling nanoparticles into macroscopic materials. Nature 382, 607-609 (1996)..Taton, T. A., Mirkin, C. A. & Letsinger, R. L. Scanometric DNA Array Detection with Nanoparticle Probes. Science 289, 1757-1760 (2000)..Tkachenko, A. V. Morphological Diversity of DNA-Colloidal Self-Assembly. Phys. Rev. Lett 89, 148303 (2002).. End-capped associative polymer chains between nanospheres: Attractions in ideal solutions. Macromolecules 33, 5713-5720 (2000)
4:45 PM - V5.6
Structure-Based Carbon Nanotube Separations by Ion-Surface Interactions.
Steve Lustig 1 , Ming Zheng 1 , Anand Jagota 2 , Constantine Khripin 2 Show Abstract
1 Central Research & Development, DuPont, Wilmington, Delaware, United States, 2 Chemical Engineering, Lehigh University, Bethlehem, Pennsylvania, United States
Single-stranded DNA wraps helically around individual single walled carbon nanotubes to form a DNA/CNT hybrid, which is both stable and dispersible in aqueous solution. Subjected to ion-exchange chromatography, a hybrid elutes at an ionic strength that depends on the electronic band structure of the core nanotube, thus providing a mechanism for separating nanotubes by chirality. We present experimental data and a theoretical model for this separation process that explains all the salient features observed experimentally to date, and provides accurate predictions for critical elution salt concentration. The competition between adsorption on the stationary phase and counterion condensation in the mobile phase is characterized by estimating the difference in free energy between the two states of the hybrid. Parametric study of the DNA wrapping geometry, SWNT dielectric properties, hybrid length and diameter indicates that the elution is most sensitive to the hybrid’s effective charge density, primarily governed by the DNA helical pitch. The model correctly predicts hybrids with metallic nanotubes are weaker binding than hybrids with semiconducting nanotubes and larger diameter nanotubes are eluted at later times.
5:00 PM - V5.7
Controlling Complementary Assembly of Peptide through Nucleobase Pairing
Rong Tong 1 , Xueyun Gao 1 , Jianjun Cheng 1 Show Abstract
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
5:15 PM - V5.8
Proton-Sweeping Role of Oligomeric Electrolyte Chains Grown on Silica Microspheres.
Xinhui Zhang 1 , Liang Hong 1 2 , Zhaolin Liu 2 Show Abstract
1 Chemical and Biomolecular Engineering, National University of Singapore, Singapore Singapore, 2 , Institute of Materials Research & Engineering, Singapore Singapore
Anionic type polyelectrolyte chains are grafted to silica microspheres (d=1μm) via surface-initiated atom transfer radical polymerization (ATRP). This grafting polymerization results in a soft and thick polymer layer surrounding the silica core according to TEM observation, which is an indicative of the existence of dense ATRP initiating sites on silica beads. Three types of vinyl monomers, namely 4-styrenesulfonate (SSNa), 3-sulfopropyl acrylate, potassium (SAP), and 3-imidazoly-2-hydroxyl-propyl methacrylate (IPMA) are employed to synthesize the grafted chains, which can be either homopolymeric or copolymeric structure. DSC investigation reveals that the grafted polyelectrolyte homopolymer chains on silica particles, though possessing low average molecular weights, exhibit stronger ionic attractive interaction than their free and long chain counterparts. Dynamic light scattering (DLS) study confirms that the polyelectrolyte-grafted silica particles possess different hydrodynamic volumes with changing of pH of the dispersion medium. Since the ATRP method offers the advantage for arranging the sequence of copolymer structure, the grafted copolymer chains consisting of IPMA and either SSA or SPA monomer units have both random and diblock chain structures. We have observed that these two chain structures bring about rather different dynamic behaviors in terms of their response to pH changes and their role in sweeping protons in the aqueous medium the particles are dispersed.
5:30 PM - V5.9
A Study of the Use of Novel Self-ordering Functionlaised Polymers to Control Crystal Growth.
Adam Ovens 1 2 , Brigid Heywood 1 2 , Nicholas Dinsdale 2 Show Abstract
1 Chemistry, Open University, Milton Keynes United Kingdom, 2 Chemistry , Keele University, Keele, Staffs United Kingdom
In this research, the ability of a series of novel oligomeric organic species to control crystal nucleation and growth of inorganic crystals was investigated. The issues under consideration were (i) the relative balance of hydrophobicity and hydrophilicity which might be programmed into a polymer; (ii) the impact metal binding, or bridging on its activity in a crystallization reaction; (iii) the mode of self organisation. An homologous series of alkyl substituted sulphonated calixarenes were used to probe these issues.The ability of a metal cation to either bridge adjacent calixarenes or to adsorb into the molecular cavity had an impact upon the interaction of these molecules with the nascent crystals; selective and specific adsorption behaviours were revealed by the expression of smooth well defined new faces in the equilibrium morphology of the crystals. When the hydrophobicity index was high (increased molecular weight of alkyl substituent) these compounds segregated at the gas/liquid interface and, as a consequence of cation-induced ordering, were able to induce the oriented nucleation of crystals. When the metal ion was preferentially adsorbed into the molecular cavity the complex induced twinning in the crystal form. These studies have revealed that, in contrast to earlier studies which argued for the only for an epitaxial relationship between the polymer and crystal, a tunable range of several chemical characteristics can be programmed into a polymeric substrates if they are to be used to control nucleation and growth.
5:45 PM - V5.10
Photochemical and Physical Characterization of Proteorhodopsin.
Chi Nguyen 1 , Hongjun Liang 1 , Jie Fan 1 , Galen Stucky 1 , Gregg Whited 2 Show Abstract
1 Chemistry and Biochemistry, University of California at Santa Barbara, Santa Barbara, California, United States, 2 , Genencor International, Palo Alto, California, United States
Proteorhodopsin is a bacterial rhodopsin protein found in marine γ-proteobacteria that functions as a light-driven proton pump. This is the first discovery where rhodopsin is found to exist in bacteria and the first instance where bacteria are observed converting sunlight into cellular energy without using chlorophyll. The unique property of proteorhodopsin affords new opportunities in the direction of bioinspired materials and applications. However, to fully realize these opportunities, we need to gain a better understanding of the photochemical and physical properties of the protein.The work presented is based on studies conducted in order to gain insight on the photochemical and physical properties of proteorhodopsin. Photochemical studies were conducted using ultraviolet-visible spectrophotometers with and without a photodiode array detector. The results showed an active protein peak at 280 nm and changes in chromophore conformation from all-trans to 13-cis upon exposure to light. Physical studies via diffusion nuclear magnetic resonance and gel permeation chromatography confirmed that due to aggregation and interaction with the surfactant, the protein is a large biomolecule that is approximately 300 kDa. It is important to note that the protein does not exist in solution without the assistance of a surfactant. Hence, the role of the surfactant and how it interacts with the protein is an important question to answer in physically characterizing proteorhodopsin.
Vivek M. Prabhu National Institute of Standards and Technology
George Fytas University of Crete
Ali Dhinojwala The University of Akron
V6: Polyelectrolyte Multilayers
Thursday AM, April 20, 2006
Room 2000 (Moscone West)
9:30 AM - **V6.1
Growth of Polyelectrolyte Multilayer Films of Polycations, Polyanions or Polyzwitterions: Correlation with Solution.
Svetlana Sukhishvili 1 , Eugenia Kharlampieva 1 Show Abstract
1 Chemistry and Chemical Biology, Stevens Institute of Technology, Hoboken, New Jersey, United States
Polyelectrolyte multilayers (PEMs) present a new class of nanostructured materials obtained through alternating self-assembly of polyelectrolytes at a solid interface. A number of applications of PEMs as coatings and separation layers have been suggested, urging better understanding of the fundamentals of self-assembly. In its first part, this talk focuses on the relationship between the multilayer growth and phase separation of polyelectrolyte complexes in solution. The deposition of polycarboxylic acid and a polycation in a wide range of concentrations of small ions is studied in situ using Fourier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR). Solution studies of the phase behavior of polyelectrolyte complexes (PECs) were done in conditions that model multilayer deposition, i.e. either with large excess of negatively charged or positively charged polymer units (φ<1 and φ>1, respectively). For different ratios of a polycation-to-polyanion chain length, R, the amount of polyelectrolytes deposited at a surface went through a maximum as a function of ionic strength, when phase diagrams of PEC in solution for both cases of φ<1 and φ>1 showed salt-induced precipitation. This suggests that to a large extent phase behavior controls the observed dependence of PEM thickness on ionic strength.In the second part of this talk, self-assembly of weak zwitterionic polyelectrolytes (e.g. carboxybetaine polymers based on poly-4-vinylpyridine, PVP-CBs) is contrasted for solution and surfaces. Depending on the pH of the external solution, self-assembly of PVP-CB is driven by two different mechanisms - hydrogen-bonding or electrostatic interactions. When performed at low pH values, self-assembly of PVP-CB with poly(methacrylic acid) results in hydrogen-bonding multilayer films which have large excess of positive charge. The deposition of such films was greatly enhanced in the presence of low molecular weight salts. The type of anion strongly affected multilayer growth and suggested a decrease in anion binding strength in a series I- > Br-> Cl-. At higher pH values, layer-by-layer deposition of PVP-CB with a range of polyanions occurred through electrostatic compensation mechanisms. The unique zwitterionic nature of PVP-CB manifested itself in the formation of novel hybrid layers in which PVP-CB is self-assembled in alternation with both polyanions and polycations. The potential of such multilayers as pH- or temperature-responsive release layers will be discussed. Finally, the correlation of pH-stability of PVP-CB-containing films with polyelectrolyte binding in solution will also be presented.
10:00 AM - **V6.2
Multilayer Assemblies from Charged Dendrimers
Wolfgang Knoll 1 , Klaus Muellen 1 , Jean-Pierre Majoral 2 , Olga Vinogradova 1 , Dong Ha Kim 1 Show Abstract
1 , Max-Planck-Institute for Polymer Research, Mainz Germany, 2 , Laboratoire de Chimie de Coordination, UPR 8241, Toulouse France
We describe the layer-by-layer build-up of ultra-thin functional assemblies by the alternate deposition of different charged dendritic nano-objects via adsorption from solution. On planar substrates we use surface plasmon optics and X-ray reflectivity measurements in order to characterize the optical properties and structural details of the assembled multilayers. We deposit either mechanically soft or shape-persistent polyelectrolyte dendrimers and compare the structural differences of the resulting multilayer assemblies. A particular issue that we address by electrochemical techniques is the question as to whether nano-porous films can be self-assembled from rigid building blocks. Finally, we also tested a novel assembly strategy based on asymmetric bis-dendrons, which are deposited by repeated deposition and (chemical) modification cycles. Using an anodized alumina layer as template we can fabricate ultrathin nanotubes with 400 nm in diameter and lengths of up to 80 μm. By alternating the deposition of dendrimers with other functional objects like metallic nano-particles or semiconducting quantum dots we can generate completely novel hybrid architectures with an interesting multi-functional performance spectrum.The coating of μ-sized spherical particles and their subsequent dissolution results in micro-capsules that we prepare from various types of dendrimers. Their mechanical properties are probed by force-compression measurements and compared with capsules made from their linear analogues.
10:30 AM - V6.3
Selective Chain Release from Layered Polyelectrolyte Films.
Eugenia Kharlampieva 1 , Svetlana Sukhishvili 1 Show Abstract
1 Chemistry and Chemical Biology, Stevens Institute of Technology, Hoboken, New Jersey, United States
The use of weak polyelectrolytes for construction of polyelectrolyte mulilayers (wPEM) offers the advantages of facile manipulation of film structure and thickness via variation of pH during polymer deposition. The pH-controlled deposition can produce novel ultrathin wPEM coatings with widely varied cell adhesion properties or the ability to absorb or release small functional molecules. This talk focuses on fundamental issues of stability and dynamics of macromolecules that are self-assembled within wPEMs. We will discuss different regimes of film response to variations in pH, and formulate criteria required for multilayer stability upon pH changes, focusing on a new regime in which one of the multilayer components is selectively released from the film. In situ ATR-FTIR was used to study the conditions for selective release of one of the macromolecular components from electrostatically assembled films upon variations of external pH. Multilayers of polymethacrylic acid (PMAA) and positively charged quaternized poly-4-vinylpyridine (QPVP) were first self-assembled at pH 5 and then exposed to a high pH. We showed that different regimes of film response at high pH can be achieved by choosing polycations with different charge densities and polyanions with different molecular weights. Selective PMAA release was observed for multilayers where PMAA was assembled with QPVP of low alkylation degree. We found kinetics of this selective chain release to be highly dependent on hydrophobic/hydrophilic balance and molecular weight of self-assembled polymers. The release kinetics of PMAA was proportional to the PMAA molecular weight in the power 1.5, suggesting reptation of PMAA chains from the film. We will also address questions of reversibility of chain release and possible structural changes resulting from chain release and readsorption. Our work provides fundamental insights on the correlation of wPEM structure and stability with chain dynamics and performance of wPEM films which are responsive to environmental stimuli.
10:45 AM - V6.4
Stability-Instability Transition of Polyelectrolyte Multilayer Thin Films on a Neutral Hydrophobic Surface
Juhyun Park 1 , Paula Hammond 2 Show Abstract
1 Materials Science & Engineering, MIT, Cambridge, Massachusetts, United States, 2 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
The formation of polyelectrolyte multilayers on neutral hydrophobic surfaces is a topic that has not been highlighted in the layer-by-layer (LBL) assembled multilayer community, although it is critical in various applications of LBL thin films formed at liquid/solid interfaces involving a noncharged, nonpolar hydrophobic surface. As a particular example of such applications, multilayer transfer printing after building up multilayers on a micropatterned poly(dimethylsiloxane) stamp, suggests a unique way for patterning multilayer nanocomposite thin films of multiple components in both two and three dimensions for practical device fabrication. Multilayering of polyelectrolytes on those surfaces is also a unique way to prepare free-standing LBL thin films for numerous important applications such as batteries, composite films with high mechanical properties, virus-arrayed thin films, membrane coatings, and the coating of microfluidic devices. However, it presents a unique challenge, and a fundamental understanding of the phenomena has yet to be provided. In this study using the polycation/polyanion pair of poly(allyl amine) and poly(acrylic acid), we explore the interplay between hydrophobic attraction of charged macromolecules to a neutral surface and their depletion from the surface. On the surface of interest, multilayer thin films can stably be deposited in a narrow window of experimental conditions when the hydrophobicity of the polyelectrolytes is enhanced by controlling the structure of the macromolecules, ionic strength, and charge density. However, the films are inherently unstable because the interactions between adsorbed polyelectrolytes and conductive media typically overwhelm those between polyelectrolytes and the insulating substrate surface, resulting in serious depletion. We investigate stability-instability transition which occurs when a stably grown multilayer thin film is exposed to an unstable medium. Various dewetting patterns, which are not yet reported for polyelectrolyte multilayers, but generally shown in metallic and polymeric thin films, are observed due to fluctuation of adsorbed polyelectrolyte chains on the surface and depletion from the surface. We show observations of this phenomenon of morphological evolution and suggest a theoretical model.
11:30 AM - **V6.5
DNAChips: Theory and Simulation of Interfaces.
B. Montgomery Pettitt 1 Show Abstract
1 Department of Chemistry, University of Houston, Houston, Texas, United States
12:00 PM - V6.6
Modeling Layer-by-Layer Assembly of Flexible Polyelectrolytes.
David (Qiang) Wang 1 Show Abstract
1 , Colorado State University, Fort Collins, Colorado, United States
Thursday, April 20New Abstract11:00 AM V6.6Modeling Layer-by-Layer Assembly of Flexible Polyelectrolytes. David (Qiang) Wang, Department of Chemical and Biological Engineering, Colorado State University, Fort Collins, Colorado.Using a continuum self-consistent field theory, we have modelled the sequential process of layer-by-layer assembly of flexible polyelectrolytes on flat surfaces as a series of kinetically trapped states. Up to 60 depositions of oppositely charged polyelectrolytes are performed, each followed by a washing step. The multilayer has a three-zone structure. An exponential growth is found for the first several layers, followed by a linear growth for subsequent layers evolving towards a steady state. Each layer inverts the total charge of the multilayer film (including the bare substrate charge). While adjacent layers are highly interpenetrating, stratification can be seen for every four or more layers. We have also examined the effects of surface charge density, bulk salt concentration, and solvent quality on the thickness and internal structure of the multilayer. Our results agree with most experimental findings on polyelectrolyte layer-by-layer assembly.