AlGaN/GaN high electron mobility transistors (HEMTs) are promising candidates for the application as transducers in biosensors. The chemical stability and biocompatibility [1] of GaN surfaces as well as their high pH-sensitivity [2] serve as the basis for this application. By covalent immobilization of enzymes on the gate area of an AlGaN/GaN HEMT one obtains an enzyme-modified field-effect transistor with the type of enzyme defining the specificity of the biosensor. Essential to this concept is the formation of an acid or a base as a product of the enzymatic reaction. The pH-change is then detected by the AlGaN/GaN HEMT in terms of a change in the gate-source voltage ΔU_GS at constant channel current, giving rise to the sensor signal. The enzyme used in the experiments presented here is acetylcholinesterase (AChE) which produces acetic acid during its enzymatic reaction by decomposing the neurotransmitter acetylcholine (ACh). Thereby, the preparation of such an acetylcholinesterase-modified field-effect transistor (AcFET) is accomplished via a wet chemical process [3, 4].
Here, the characteristics of AcFETs were analyzed by measuring ΔU_GS in dependence of the concentration of administered acetylthiocholine iodide, an ACh analogue, and evaluated applying a kinetic model [5] that yields microscopic parameters representing both the enzymatic activity (by the Michaelis constant K_M) and the transistor/enzyme/electrolyte system (by the normalized exchange rate constants across the respective interfaces).
The utilization of AcFETs allows for monitoring of the release of the neurotransmitter ACh and, hence, the activity of neurons. This is shown here on the example of myenteric neurons from 5-8 days old Wistar rats, cultured on the gate area of the AcFETs, with the release of ACh induced by a potassium chloride stimulus. The recorded AcFET signal due to the chemical stimulus is related to the enzymatic activity of the covalently immobilized AChE.
Concluding, on the one hand our results show that AcFETs based on AlGaN/GaN HEMT structures provide a suitable platform not only for the realization of a specific biosensor but also for the analysis of the functionality of immobilized AChE. On the other hand we have been able to monitor the activity of myenteric neurons non-invasively and thus converting a biological into an electrical signal.
[1] G. Steinhoff et al., Adv Funct Mater 13 (2003), 841
[2] G. Steinhoff et al., Appl Phys Lett 83 (2003), 177
[3] B. Baur et al., Appl Phys Lett 87 (2005), 263901-1
[4] K. Gabrovska et al., Int J Biol Macromol 43 (2008), 339
[5] S. Glab et al., Analyst 116 (1991), 453

Combined systems of semiconducting polymers and aqueous electrolytes are emerging as the new frontier of organic electronics, with many promising applications in biology, neuroscience and medicine. A detailed characterization of polymer/water interfaces is thus urgently needed. In particular, the combined effect of contact with electrolytes and visible illumination should be taken into account, since many applications rely on exposure to light, or are meant to work in ambient room light conditions.
In this work, we first extensively characterize the chemical-physical processes occurring in thin films of poly(3-hexylthiophene) exposed to water saline solutions and visible light. Through combination of different spectroscopic techniques, we demonstrate that prolonged contact with saline solutions does not add further degree to photo-activated doping processes of the polymer; instead, it turns out that the reduced number of oxygen molecules present in water, compared to open air, acts as a limiting factor, thus fully validating the use of semiconducting polymers in contact with electrolytes.
In addition, we demonstrate that the recently demonstrated technique of cell stimulation by polymer photo-excitation (CSP) represent a versatile platform for full-optical control of cell excitation/inhibition. We report examples of functional interfaces between several combinations of conjugated polymers and different cell cultures (HeK cells, astrocytes, neuronal networks). A detailed model of the mechanisms occurring at the polymer/electrolyte interface and leading to cell photoexcitation, based on electrical and optical measurements, will be finally presented and critically discussed

A visible trend over the past few years involves the application of conducting polymer devices to the interface with biology, with applications both in sensing and in actuation. Examples include biosensors, artificial muscles, and neural interface devices. The latter are of particular interest, as conducting polymers offer several distinct advantages compared to incumbent technologies, including mechanical flexibility, enhanced biocompatibility, better signal-to-noise ratio and capability for drug delivery. As such, they promise to yield new tools for neuroscience and enhance our understanding on how the brain works. After a brief introduction, I will present a few examples of electrodes and transistors for applications ranging from recording brain activity inside the skull to cutaneous recordings of muscle movement. In vivo performance, electrical characteristics and properties such as mechanical flexibility and biocompatibility will be discussed.

The miniaturization of bioelectronic intracellular probes opens up opportunities to study functional structures inaccessible by existing methods and to interrogate biological systems with minimal invasiveness. Here, we report the design, fabrication and demonstration of the intracellular bioelectronic probes with size down to sub-10-nm regime based on a nanowire-nanotube heterostructure, in which nanowire FET detectors are synthetically-integrated with the nanotube cellular probes. Water-gate measurements together with numerical simulations show that devices with probes sizes as small as 5 nm, which approaches the size of a single ion channel, have sufficient time response to resolve fast electrical signals in live cells. The use of phospholipid modification enabled spontaneous penetration of the cell membrane by the nanotube probe, and allowed full-amplitude, stable recording of intracellular action potentials by these ultra-small bioelectronic probes. Furthermore, simultaneous multi-site recording from both single cells and cell networks, and the recording of low frequency transmembrane potential demonstrated the capability, robustness and reliability of these ultra-small bioelectronic probes for intracellular interrogation and their potential for neural and cardiac activity mapping.

Debilitating neurological disorders such as Parkinson&’s disease and essential tremor are often treated via electrical stimulation using implantable devices. However, such procedures are highly mechanically invasive as well as not specific to cell type. Conversion of alternating magnetic fields in the radiofrequency range into heat via hysteretic power loss in superparamagnetic nanoantennas has been used to remotely control gene transcription in vivo and action potential firing in vitro. This actuation of TRPV1, a heat-sensitive calcium ion channel, with magnetothermal conversion may lead to minimally-invasive deep brain stimulation therapies. However, the timescale required - tens of seconds - suggests that further optimization to this magnetothermal approach is needed to shorten the actuation time to biologically relevant timescales.
Recently, we have applied a dynamic hysteretic model to optimize the magnetic nanomaterials properties, which allowed us to achieve record heat dissipation rates in magnetic nanoparticles (MNPs) at physiologically safe driving conditions. We find that iron oxide nanoparticles ~22 nm in diameter can reach temperature changes needed to trigger TRPV1 an order of magnitude faster than what was previously achieved at field frequencies and amplitudes relevant to magnetic hyperthermia. By sensitizing neurons to heat using a viral delivery system for TRPV1 DNA, we demonstrate how the heat dissipative abilities of our MNPs can be harnessed for minimally invasive deep brain stimulation therapies in vivo. Such an approach has implications towards remote control of biological functions at a single-cell level.

Mechanical cues affect cell behavior. In vitro, neurons and supporting cells show distinct response to substrate stiffness and topography. In vivo, and in particular for long-term implantations, the physical properties of the implant are key to maintain a stable, non-damaging, connection between the nervous tissue and the electrodes. The mechanical mismatch at the soft neural tissue to hard implant material interface combined with local micromotions induces an inflammatory reaction by immune cells, the generation of fibrotic tissue and/or a scar capsule, withdrawal or death of the nearby neurons and progressive loss of electrode contact, and thus implant failure.
We hypothesize that microfabricated electrode implants mechanically matched to the surrounding tissue may be a robust technological route for chronic synthetic neural implants. To do so, soft electrode implants are prepared with silicone elastomers. With elastic moduli as low as 10skPa, elastomers are some of the softest materials still compatible with MEMS-like fabrication processing. Furthermore their surface can be engineered in the form of large-area matrix of elastic micron-sized pillars thereby producing an interface with even lower stiffness.
We will review the materials and fabrication process to produce soft neural electrodes then illustrate the potential of this “soft technology” in the context of peripheral nerve interfaces and spinal cord electrode implants.

The development of advanced biomedical devices capable of real-time stimulation and recording of neural cells bioelectrical activity is a demand to improve our understanding of the functional mechanisms of the Nervous System and the need for effective in vitro drug screening targeted to neuropathophysiologies.
Organic semiconductor materials which combine long-term biocompatibility and mechanical flexibility are suitable candidates for neural cell interfacing. Of particular relevance is the study of the effect of the material interface interaction with neural cells, namely neurons and astrocytes. In particular, the material interface should support the cells adherence and promote their growth and differentiation on the device structure. The cell bioelectrical activity should be preserved, avoiding alteration of the electrophysiological properties due to the interaction with the organic semiconductor. Here, we show that primary neurons and astroglial cells can adhere, grow and differentiate on a suitably engineered perylene-based field-effect transistor platform, while maintaining their firing properties even after a prolonged time of cell-culturing. The development of transparent Organic Cell Stimulating and Sensing Transistors (O-CSTs) that provide bidirectional stimulation and recording of primary neurons is also reported. We demonstrate that O-CST enables depolarization and hyperpolarization of primary neurons membrane potential. The transparency of the device also allows the optical imaging of the modulation of the neural cell signalling. The O-CST device enable extracellular recording from neurons with maximal amplitude-to-noise ratio 16 times better than a micro electrode array (MEA) system on the same neuronal preparation. Our organic cell stimulating and sensing device paves the way to a new generation of devices for stimulation, manipulation and recording of neural cell bioelectrical activity in vitro and in vivo.
Supported by EU-FP7-ITN Olimpia, Firb-Futuro in Ricerca, SILK.IT

The goal of this project is to develop a nanoprobe device for intracellular electrical signal recording and stimulation of neuronal cells. This paper presents a platform that integrates “Fin” shaped nanoelectrodes and cell microprinting technology. The “Fin” shaped nanoeletrodes were designed to increase the electrode area and conductance so as to reduce the signal loss seen in the case of traditional circular nanopillar designs. The microprinting technology, in turn enables controlled number and volume of cells to be printed on top of the nanoeletrodes in order to realize ease in cell penetration.
The overarching goal of neuroscience is to target and discover the relationships between the functional connectivity-map of neuronal circuits and their physiological or pathological functions. In the past, extracellular microelectrode arrays (MEAs) have been used to record and stimulate a population of excitable cells for months in-vivo (Kipke et al.). The recorded spikes (signal) by extracellular electrodes, though informative, do not provide the source mechanism for neuron firing; because the extracellular recordings do not record synaptic signals (subthreshold). On the other hand, intracellular recording can help study the functions of “silent” neurons and neuroplasticity (Spira et al.). In this respect, the current intracellular recording technologies include a sharp or patch electrode to measure only a few neurons. For recording a record large number of neurons, technologies such as gold mushroom-shaped microelectrodes (Hai et al.), vertical nanowire electrode arrays (Robinson et al.) and nanoFET technology (Tian et al.) are currently under development. The gold mushroom-shaped electrodes in order of microns are invasive for smaller cells with no successful recording on rat hippocampal neurons and primary rat cardiomyocytes. The vertical nanowire electrode arrays show high electrode impedance which causes large signal loss. The nanoFET show higher noise levels and the manipulation of a single nanotube to penetrate a single cell are very challenging. In this work, we present the design and fabrication of “Fin” shaped nanoelectrode which seeks to overcome the restrictions between electrode impedance and electrode size. Compared to the 3x3 array of 150 nm diameter nanowire electrodes, the “Fin” electrodes reduces impedance by factor of ten. 150 nm thick fins are seen to be less damaging compared to mushroom-shaped electrodes. We demonstrate the ability of microprinting technology to print viable neuronal PC12 cells onto pre-defined areas such as within the reservoir with nanoelectrodes. The relationship between the electrode geometry and neuronal cell viability is studied. Finally, the intracellular neuronal activity (action potential) with and without sub-threshold (10-40mV) electrical stimulus, along the effect of electrode surface coating on signal coupling is presented.

Due to their structural kinship to proteins, carbohydrates and nuclei acids, the use of organic conducting polymers in biomedical research and medical applications is highly intuitive from a biological and chemical perspective. The availability of organic chemistry toolkits to functionalize and adapt these molecules, convenient processing techniques like soft lithography, electrodeposition or vapor phase polymerization as well as the possibility to reversibly modify their chemical and electrical properties by switching between the redox states of the conducting polymer backbone qualifies them as interesting materials for the development of functional tissue-device interfaces.
Using organic electronic devices with different designs and polymer bases, one can achieve control of cell growth and attachment on different levels. On a surface switch based on the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with tosylate (PEDOT:tosylate) we show modulation of epithelia formation by presenting electrochemically oxidized versus reduced surfaces as substrates for cell attachment. By further modification of the device, adding a channel and gate electrode, an organic electrochemical transistor (OECT) is developed, which allows for active control of epithelial cell-density gradients along the channel. Electronic control of cell release was demonstrated in a similar devices using the self-doping compound PEDOT-S:H.
Organic electronic devices can also be designed to facilitate modulation of cell signaling in a biomimetic fashion. Electrical actuation of neuronal cells in a three dimensional nano-fiber scaffold is achieved on an electrospun scaffold coated with PEDOT:tosylate. The unique property of organic electronics to utilize both electrons and ions as charge carriers is used in the organic electronic ion pump (OEIP). When addressed electronically, the OEIP translates electronic signals into electrophoretic migration of ions or neurotransmitters. The precise, spatiotemporally controlled delivery of signaling substances in absence of liquid flow was demonstrated as a novel interface to modulate mammalian senses.
This presentation will highlight the potential of communication interfaces based on conjugated polymers in generating complex substrate signaling to control cell and tissue physiology. Organic electronic devices will have widespread applications across basic medical research fields as well as future applicability in medical devices in multiple therapeutic areas.

The study of interconnectivity within neural networks is limited by the existing experimental techniques for massively parallel electrical recordings. Multielectrode arrays and patch clamps are the current standards for recording neuronal membrane potentials; however, neither offers the combination of sensitive, long-duration recordings. Developing solid-state devices via scalable fabrication techniques requires thoughtful design informed by the conditions at cell surfaces. To achieve sensitive, long-term recordings, we target biomimetic integration of probes with the plasma membrane, using a layered structure we describe as “stealth probes.” Stealth probes are solid-state nanostructures that can span cell membranes, forming electrically tight seals against the phospholipid bilayer structure. The junction between probe and cell is both mechanically stable and offers high resistance against ion exchange between cytoplasm and media. Gigaohm-level leak resistance is the critical need for non-invasive intracellular measurements with the scalability of a multielectrode array. Through cell-probe interface modeling, we have identified the parameters required for sensitive cellular electrical recordings, and are employing fabrication techniques to target devices accordingly. We have developed a hybrid on-wire lithographic approach to fabricate biologically compatible, individually addressable solid-state nanoelectrode arrays. Here, we describe device fabrication and the necessary parameters for sensitive electrophysiological recordings. We focus on the electrical characteristics of the probes, the relationship between device impedance and signal-to-noise ratio, and the requirements necessary for immediate deployment of the technology for experiments in neuroscience.

Conducting polymers (CPs) are easy to process and have tunable physical and chamical properties including conductivity, volume, color, and hydrophobicity. Therefore, these organic polymers are attractive in a broad spectrum of biomedical applications ranging from implentable electornics, and biosensing to tissue engineering and drug delivery. Among CPs, polypyrrole (PPy) is particularly appleaing for biomedical applications due to its biocompatibility and excellent stability. PPy can be electropolymerized into thin films and serve as substrates for in vitro cell cultures. Patterned films of conductive polymers, particularly with various surface chemistries, provide an excellent platform to study cellular behavior. We recently introduced a unique and verstaile method for direct patterning of PPy films on gold substrates. In this method, we employed an agarose hydrogel stamp as a carrier of polymer precursor solution including pyrrole and dopants. Upon placement of the stamp on an electrode and subsequent application of a current, the polymerization of pyrrole only occurred in the contact areas between the topographically-patterned hydrogel and the gold substrate. We demonstrated the capability of this method to generate positive patterns of PPy films with different sizes and geometries in a single-step and solution-free process. More importantly, we demonstrated that the posts on a hydrogel stamp can deliver different monomer/dopant combinations to create a patterned PPy film with different and addressable surface chemistries in a parallel fashion.
Here, we aim to apply this innovative and multifaceted technique to cage bioactive molecules within the CP network by simply adding the desired biomolecules to the polymer precursor solution that is applied for inking the hydrogel stamp. We hypothesize that the biocompatible agarose gel stamps can safely deliver the bioactive molecules during the electropolymerization process, leading to the entrapment of these molecules within the CP film. We tested this hypothesis by incorporation of D-biotin molecules into PPy network and confirmed the presence of D-biotin in these films by fluorescence immunohistochemistry and ATR-FTIR. Most importantly, we demonstrated that this hydrogel-mediated electrodeposition technique can create spatially addressable patterned films of PPy decorated with multiple different proteins and biomolecules in one-step process. Currently, we are employing these bio-functionalized PPy films to control and study neuronal cell adhesion and differentiation. The goal of this study is to apply these biofunctionalized PPy films to control stem cell fates for applications in neural tissue engineering.

Ever since the pioneer titanium alloy (Ti6Al4V) has been used as biomaterial, lack of biocompatibility has been extensively reported and propelled research on improved materials with appropriate mechanical behavior and adequate biocompatibility. Studies have indicated that vanadium produces oxides harmful to the human body; in order to replace vanadium containing Ti alloys, Ti-6Al-7Nb was developed. Today this alloy is the preferred choice for cementless total joint replacements. It is very important to produce a nanostructured bioactive metal implant with appropriate mechanical properties and we applied a chemical and thermal treatment that converts the surface of titanium alloy into bioactive surface. Therefore, bioactive Ti6Al7Nb might represent an alternative for advanced orthopedic implants under load-bearing conditions.
Eleven mini-pigs weighting around 50 kg, with free access to food pellets and water, were the experimental animals for this study. Ten of these pigs (one is the control) were anesthetized and after shaving, disinfection and draping, a straight 3 cm incision was made and the implants (plate and pin) were implanted into the epiphyses of the tibiae. Surgical procedures were performed bilaterally. At 6 months after implantation, the mini-pigs were sacrificed.
After sacrifice, the segments of the proximal tibia epiphyses containing the implanted plates and pins were cut off, fixed in phosphate-buffered formalin and dehydrated in serial concentrations of ethanol after which they were embedded in polyester resin and then cutted and grounded to a thickness of 75-100 µm. With these samples SEM-EDX examinations were made. The aluminium content was measured by electrothermal atomic absorption spectrometry in different organs: brain, fat, kidney, spleen and liver.
All the results revealed that the plates and pins are in direct contact with newly formed bone without any intervening soft tissue layer. No aluminium accumulation occurs during the experiment and we regard it as one of the advantages of this implant in consideration for clinical applications.

Conducting polymers (CPs) have been the subject of significant research in recent years for their optical and electronic properties, as well as their potential use in biomedical applications. Medical procedures requiring electrical stimuli have traditionally used metallic compounds, which have severe issues with tissue compatibility. CPs are a promising replacement to metals in these applications due to their biocompatibility, electrical conductivity, and range of chemical and physical properties. However, standard CPs are typically brittle and difficult to process into 3D structures which has limited their use. We aim to develop new CPs that incorporate a peptide motif based on an amino acid sequence found in silk fibroin that is capable of self-assembly and is responsible for the characteristic strength of silk. We hypothesize that hydrogen bonding between chains of the peptide functionalized conducting polymers will influence the 3D organization and improve mechanical strength while retaining biocompatibility. To make such materials we are investigating two complimentary approaches: 1) assembling and polymerizing peptides containing a thiophene-based monomer or 2) functionalizing a pre-made polymer with silk peptides. Here, we present the synthesis of silk-inspired peptides coupled to 3,4-ethylenedioxythiophene (EDOT) monomers, the characterization their electrochemical properties, and their capability to self-assemble. We also demonstrate the ability to incorporate these thiophene-peptide conjugates into copolymers with EDOT.

Implantable biomedical devices such as emerging MEMS-based neural prostheses require long-term stability in the human body. Since these devices cannot be protected with conventional metal or ceramic enclosures, a conformal encapsulation that provides chronic protection against water and ion ingress is necessary to achieve this goal. Commonly used materials include some urethanes, silicones, ceramics and metals. Amorphous silicon carbide (a-SiC) was proposed as a protective coating due to its biocompatibility and low dissolution rate in saline compared to other commonly used dielectric materials for IC passivation, such as silicon nitride (SiNx) and silicon dioxide. In addition, the deposition, patterning and etching of SiC are compatible with standard CMOS processing. These factors provide a strong incentive to investigate the potential of a-SiC as a protective coating for implantable devices.
In this study, we examined the properties of a-SiC deposited at 325°C by plasma enhanced chemical vapor-phase deposition (PECVD). We focused on three properties of a-SiC that are critical to its success as a protective coating: dissolution rates in accelerated saline tests, pinholes, trench coverage and barrier properties. The existence of any pinhole in the SiC layer will expose the underlying materials to the physiological medium causing them to dissolve, adversely affecting functionality of electrical devices, and inducing biological response in the human body. We performed a fast pinhole test by immersing the device in selective SiO2 and Si etchants and found that SiC films as thin as 200nm protected the front surface of MEMS devices completely with no evidence of pinholes. We demonstrated that SiC is able to cover most of the regions inside deep trenches (with an aspect ratio of 6:1), while a small number of pinholes were identified on the sidewalls. Further research is needed to eliminate these pinholes.
To test stability of the silicon device with polysilicon-filled trenches protected by a-SiC in the biological medium, we soaked both protected and unprotected devices in saline at 87°C for 12 days, which is equivalent to ~ 1 year at the human body temperature. SEM images showed that devices without a-SiC coating degraded significantly, while devices with a SiC coating stayed mostly intact. We also examined the forward and reverse I-V characteristics of pn junctions underneath the SiC coating before and after soaking, and observed no significant difference. These results indicate that a-SiC provided an effective barrier for our MEMS-based retinal prosthetic implants.

Biocompatible materials capable of conducting electricity have numerous biomedical applications including use as electrodes for neurological stimulation and recording, artificial muscles, and stimuli-responsive sensors. Conducting polymers (CPs) such as poly(pyrrole) and poly(thiophene) are advantageous for these applications as they are biocompatible, and their chemical and physical properties can be easily tuned. A major hurdle in the development of practical biomedical devices utilizing conducting polymers is dealing with the poor mechanical properties of the bulk polymers. The conjugated π-system of CPs that allows electron flow also results in the bulk material being stiff and brittle, complicating the fabrication of three-dimensional electrodes. In order to improve the mechanical properties of CP networks, we have established methodology for the fabrication of composites materials made of (poly)pyrrole interpenetrating into a flexible silk fibroin scaffold. Silk fibroin is a well-studied biomaterial capable of being processed into a variety of forms, such as films, hydrogels, and 3D scaffolds. Here we present new electropolymerization strategies to increase the conductivity and versatility of these silk-CP composites, and methods to tailor their surface morphology to maximize performance.

Optical analysis of deep brain structures has remained an elusive challenge, due to the presence of highly scattering, randomly distributed, dense lipid bilayers surrounding neurons. Though laser scanning coherent anti-Stokes Raman scattering (CARS) microscopy has been successful in rendering three-dimensional (3D) spatial resolution in live cells and tissues, light dispersion still reduces laser intensity and signal quality, and prohibits imaging of deeper targets without first making incisions to access the tissue. This problem may be addressed by using a newly developed technology, known as CLARITY, which enables unprecedented resolution of detailed structural and molecular information of intact biological systems. During CLARITY sample preparation, intact tissue (such as whole brains) can be transformed into nanoporous tissue-polymer hybrids, which are then made transparent using electrophoretic lipid removal. The final product of CLARITY is tissue that has been stabilized through effective replacement of structure-maintaining lipids with a hydrogel covalently bonded to proteins. The resulting transparency of the tissue-polymer hybrid permits true high resolution, 3D analysis of neural networks and biomolecular architecture by much simpler, less damaging, and cost-effective imaging techniques. In this study, we investigated polymer formation and hybridization within tissue using confocal Raman scattering, complemented by two-photon fluorescence microscopy. This work represents the first demonstration of three-dimensional Raman spectral mapping of brain tissue, providing a new perspective on the distribution and identity of protein and polymer bonds. Information from these maps can be correlated with biological features identified using appropriate staining techniques and two-photon microscopy, and can be employed to quantitatively explore the influence of key reactants on CLARITY tissue-polymer hybrid properties. These results will be significant in helping to tune the CLARITY platform for various applications, and provide a deeper understanding of how polymers form and crosslink within tissues.

Natural-origin hydrogen-bonded molecular solids such as the indigo and its derivatives are very promising semiconducting materials because of remarkable physical and chemical properties as well as biocompatibility and biodegradability. With mobility in the range of 1 cm2/Vs and stable operation in air, they are competitive with many synthetic materials. In recent years, we have demonstrated that it is possible to produce green electronic devices using the indigo compounds. In this report, we bring our recent works into practical implementations of electronic circuits, such as complementary-like voltage inverters and ring oscillators, where indigo and its derivatives are remarkable for their air stability.

As an artificial cell membrane on solid wafer surface, supported-lipid bilayer (SLB) is one of most promising biological platform in biophysics research because it opens possibilities to study the fundamental properties of cell membrane by modern surface-based characterization techniques and advanced nanotechnology. In the meantime, carbon nanotubes (CNTs), as a typical one-dimensional molecular system, have been attracted enormous attentions for their remarkable electrical properties and CNT-based field effect transistors (FETs) have shown high sensitivity in bio- or chemical sensors. However, a challenge is how to engineer graphene&’s sensitivity to a specific analyte of interest.
Here, we incorporate ion channel membrane proteins gA and α-HL in an SLB on a functionalized all-semiconducting nanotube network, where SLB forms an insulating barrier on FET surface. The nanotube transistor as a charge sensor only detects the ions or biomoleculars through ion channels. Nonetheless, due to the nature hydrophobic surface of carbon nanotube, lipid bilayer doesn&’t form a continuous film on high-density nanotube network surface. At the same time, the main drawback of solid supported lipid bilayer is the very limited distance between solid substrate and lipid bilayer, usually only up to 1nm. Therefore, it is crucile to utilize surface functionalization for fabricating a robust lipid bilayer on surface and spacing the membrane up from the substrate. Our functionalization strategy is using silane molecular as a linker to covalently bind with substrate and lipid monolayer. The space distance can be delicately tuned by changing the length of silane molecular. The second layer lipid layer can be easily formed on the tethered lipid surface by vesicle fusion or directly dropping lipid ethanol solution. The quality of lipid membrane is estimated by fluorescence recovery after photobleaching (FRAP), atomic force microscopy (AFM) and impedance spectroscopy. Moreover, combining with microfluidic channel, we are able to detect single ion channel activity. Dynamic opening and closing of the pores is observed through measurement of the current from the nanotube network, through the nanopores, and into solution. The all-semiconducting nanotube network devices are compatible with microfabrication process, opening a window for massively parallel manufacturing of nanotechnology for a variety of applications in electrophysiology and biosensors.

We have recently demonstrated how we can use charge trapping/detrapping in an array of gold nanoparticules (NPs) at the SiO2/pentacene interface to design a SYNAPSTOR (synapse transistor) mimicking the dynamic plasticity of a biological synapse. This device (memristor-like) mimics short-term plasticity (STP) [1] and temporal correlation plasticity (STDP, spike-timing dependent plasticity) [2], two "functions" at the basis of learning processes. A compact model was developed [3], and we demonstrated an associative memory, which can be trained to present a pavlovian response [4].
Here we develop an electrolyte-gated version of this device for biocompatible applications. We report on a detailed understanding of the electrical behavior of these synapstors in physiologically relevant conditions. We compare synapstors operated by the traditional bottom gate structure in air and by a water-electrolyte gate geometry. We show that the increased capacitance of the pentacene/water interface leads to a large improvement of the synapse-like behavior of these devices. STP of comparable amplitude (about 50% of the total output current) is observed at a reduced working voltage (i.e. spike voltage of 0.4V in water, instead of 10 V in air). Moreover, the typical dynamic time response of the synapstor is also decreased by about a factor 10 (ca. 0.2s instead of ca. 2-5s). These last results represent major improvements towards the use of these organic/NPs synapstor in biocompatible application e.g. as synapse prosthesis.
This work has been financially supported by the EU 7th framework programme [FP7/2007-2013] under grant agreement n° 280772, project "I ONE”.
References
[1] F. Alibart et al., Adv. Func. Mater. 20, 330 (2010).
[2] F. Alibart et al., Adv. Func. Mater. 22, 609-16 (2012).
[3] O. Bichler et al., IEEE Trans. Electron. Dev. 57(11), 3115-3122 (2010).
[4] O. Bichler et al., Neural Computation 25(2), 549-566 (2013).

Materials capable of controlled movements that can also interface with biological environments are highly sought after for biomedical devices such as valves, blood vessel sutures, cochlear implants and controlled drug release devices. Here we report the synthesis of films composed of a conductive interpenetrating network of the biopolymer silk fibroin and poly(pyrrole). These silk-PPy composites function as bilayer electromechanical actuators in a biologically-relevant environment, can be actuated repeatedly, and are able to generate forces comparable with natural muscle (>0.1 MPa), making them an ideal candidate for interfacing with biological tissues. We will discuss the mechanical properties and actuation performance of these promising devices under biologically relevant conditions.

Currently there is enormous interest in organic electronics devices.Such organic devices may aid the development of new technologies such as OFETs, OLEDs and OPVs that were active in clean energy production. Melanin that is an organic biopolymer, has great potential, as an active component in these devices. Recently soluble melanin derivatives have been obtained by a synthetic procedure carried out in DMSO (D-melanin).[1] In this work a comparative study of the structural characteristics of synthetic melanin derivatives obtained by oxidation of L-DOPA in H2O and DMSO is presented. To this end, Fourier-transform infrared spectroscopy as well as, proton and carbon nuclear magnetic resonance techniques have been employed. In addition, aging effects have been investigated for D-melanin. The results suggest that there is incorporation of sulfonate groups (-SO2CH3), from the oxidation of DMSO, into melanin, which confers protection to the phenolic hydroxyl group present in its structure. The solubility of D-melanin in DMSO is attributed to the presence of these groups. When the obtained melanin is left in air for long time periods, the sulfonate groups leave the structure, and an insoluble compound is obtained. NaOH and water have been used, in order to accelerate the release of the sulfonate groups attached to D-melanin, thereby corroborating the proposed structure and the mechanism suggested for the synthetic procedure. In this work we study also the influence of temperature on D-Melanin synthesis and properties. To this end, UV-Vis and Fourier-transform infrared (FTIR) spectroscopy techniques have been employed to analyze D-Melanin synthesized in the range of 25 C to 100 C. Through UV-Vis spectroscopy, it was possible to follow the process of polymerization and the optical properties of D-Melanin under different syntheses conditions. The increase in synthesis temperature enhances the reaction kinetics and also influences the elimination of carbonyls present in the monomers, thus facilitating the polymerization of D-Melanin. Another consequence of synthesizing at higher temperatures is an easier control of the reaction product.
[1] S.N. Dezidério, C.A. Brunello, M.I.N.da Silva, M.A. Cotta, C.F.O.Graeff,
Journal of Non-Crystaline Solids, Vol.63 (2004) 338-340.

How well a protein conducts electrons depends on how well the protein is coupled to the contacts via which currents are measured and voltage applied and the electronic coupling across the protein. Assessing the importance of each of these couplings will help understanding electron flow across proteins. Using monolayers of Cyt C we find that chemical protein-contact binding improves room temperature conduction twofold and halves the activation energy for steady-state hopping. At low (< ~ 150K) temperatures, where transport is by tunneling via super-exchange, covalent binding increases conduction up to 10-fold. The importance of coupling across the protein is shown by changing the protein&’s orientation, relative to the electrodes, using seven different mutants. Remarkably, currents do not depend on the distance between electrodes, defined by the orientation of each electrode-bound mutant, of either room temperature or 30K currents. Rather, the distance between the heme group and the top or bottom electrode affects the ETp process. In general, mutants with proximal heme have lower thermal activations at higher temperatures, and higher conductance at low temperatures (temperature-independent regime), than those with a distal heme. Thus, while illustrating and emphasizing the importance of covalent binding, we find that factors beyond simple geometrical ones need to be considered, to describe ETp across proteins, a finding that warrants further study.

Graphene nanoribbon-nanopore (GNR-NP) sensors offer the potential, because of their thickness, for ultimate spatial resolution at high measurement bandwidth for single-molecule DNA analysis and sequencing. We developed graphene nanoribbons (GNRs) (width: down to 20 nm, length: 600 nm, on 40 nm thick silicon nitride (SiNx) membranes) that can sustain micro ampere currents at low voltages (sim; 50 mV) in buffered electrolyte solution and exhibit a sensitivity to local potential of ~ 1% / mV, enabling high bandwidth sensing (>1MHz). GNR conductance measurements, conducted in situ inside a TEM operating at 200 kV, show that during nanopore formation and imaging, GNR resistance increases linearly with electron dose and that GNR sensitivity decreases by a factor of ten or more upon exposure at high magnification. We present a methodology for forming a nanopore at the edge or in the center of a nanoribbon in scanning TEM (STEM) mode, in which the position of the converged electron beam can be controlled with high spatial precision via automated feedback, that minimizes the exposure of the GNRs to the beam before and during nanopore formation and preserves the high conductivity and sensitivity of the GNR-NP sensors.

Charge transfer across the biotic-abiotic interface remains to be a significant obstacle for the integration of biological and electronic systems in high-performance bioelectronic devices. In our approach to modify the biotic-abiotic interface, easily accessible synthetic constructs of tunable properties, namely, conjugated oligoelectrolytes (COEs) are utilized to improve charge extraction in microbial fuel cells (MFCs). COEs are small organic molecules characterized by an electronically delocalized, hydrophobic backbone-bearing pendant charged, hydrophilic functional groups. Arising from these molecular features, COEs are water-soluble and amphiphilic in nature, which allow them to spontaneously intercalate into lipid bilayers and cell membranes. COEs have demonstrated the ability to facilitate electron transfer across a supported lipid bilayer, which lead to their introduction into biological systems for the improvement of transmembrane charge transport. In pure culture systems such as yeast and E. coli biofuel cells, enhanced current generation is observed with the addition of COEs, such as (4,4&’-bis(6”-(N,N,N-trimethylammonium)hexyl)amino)-styryl)-stilbene tetraiodide (DSSN+). The increase in performance is also observed in mixed consortia systems such as wastewater MFCs, along with a corresponding increase in organic contaminant removal. Recent results indicate that COEs are not only increasing the current generation but also decreasing the internal resistance of the fuel cell, contributing to the overall increase in power density. To fully understand the participation of COEs in the overall improvement of MFC performance, electrochemical impedance spectroscopy (EIS) and polarization techniques are used to characterize the limiting factors that are decreased by COE addition in both mixed consortia and E. coli fuel cells. The ability of these nontoxic, synthetic COEs to mediate transmembrane charge transfer without acting as conventional redox shuttles suggests the potential for future applications in the field of bioelectronics.

Hybrid organic/inorganic nanostructures are engineered to function as two terminal devices with enhanced functionality. The devices are the building blocks for designing hybrid organic/inorganic circuits in the nanoscale. In our work, we have demonstrated the sensing capabilities of electrospun conducting polyaniline nanofibers for designing nanoweb devices towards detection of biomolecules.
In electrospinning, the nanofibers formed by the evaporation of the solvent from the electrified polymer jet are randomly aligned. Deposition of electrospun nanofibers in desired alignment can be achieved through the careful selection of the collector geometry. In this work the polyaniline nanofibers of diameter in the range 50-300 nm was obtained by controlling flow rate and the applied voltage. Nanofibers of defined morphology were deposited in an ordered pattern on a non-conducting collector substrate patterned with metal microelectrode array. Concentration below the critical entanglement concentration of the polymer solution resulted in the formation of beaded fiber matrix. The device designed in this research comprises of a glass substrate with a metal microelectrode array of a crossbar array configuration and was used for electrical characterization of polymer cross bar junction. With the described technique the polyaniline nanofibers were directly patterned at the crossbar junction. The electrically active area comprises of gold nanoparticles embedded in the nanofiber matrix.
Biomolecules with surface charge such as nucleic acids were detected on this device by interfacing the biomolecules with the polymer/metal composites. The change in electrical properties due to modulation in charge transport at the crossbar junction is used to obtain switching behavior was identified as the measured electrical signal for designing sensors. Nanotextured surface offers strong charge carrier transport and hence enhances the strength of the detected signal. This device is used to quantify the hybridization event of DNA molecules. The hybridization event at the crossbar junction effectively modulates the charge transfer kinetics and modifies the junction characteristics due to the surface potential associated with the organic molecules. The net change in surface charge can be measured either as changes in the diode current in the two terminal configuration or as changes in the source- drain current in the three terminal configuration. Smaller the fiber diameter, larger is the surface area for immobilization of DNA molecules and higher the sensitivity of the device. Detection sensitivity in the order of fg/mL was targeted by measuring the voltammetric current response (in microamperes). This was measured between -3V and 3V. The switching behavior is observed when the change in the measured current is higher than three orders of magnitude.

Cortisol “a steroid hormone” is known as a potential biomarker for psychological stress estimation and abnormality is indicative of many disorders. A simple, low-cost, label free sensor is required to detect Cortisol. Electrochemical immunosensors due to increased range, rapid detection, and sensitivity have been developed to detect Cortisol. The sensing performance is dependent on the functionality and electrical behavior of immobilizing matrix for high electron transport for signal amplification and loading of higher biomolecule.
In recent studies, nonmaterials have been deposited usually on Au or Au-coated silicon or glass or other hard substrate, which was then used as a sensing device for biosensing. Nanomaterials grown on flexible and wearable plastic substrates are suitable to biomedical instrumentation as they reduce the weight and cost of the device.
In this work, nanostructured ZnO due to bio compatibility, chemical stability, high iso electric point, electrochemical activity, high electron mobility, ease of synthesis and high surface-to- volume ratio has been explored for electrochemical Cortisol immunosensing. ZnO nanostructures synthesized by Sonochemical method are used to immobilize Ant-Cortisol antibody (Anti-Cab). ZnO nanorods and nanoflakes are directly synthesized on ITO/PET as flexible substrates at ambient conditions by reacting Zinc acetate dehydrate (Zn (O2CCH3)2 .2H2O), zinc nitrate hexahydrate (Zn (NO3)2. 6H2O) and hexamethylenetetramine (HMT, (CH2). 6N4) in aqueous solutions. The selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM) studies on the nanostructures showed that the nanostructures grown are single crystalline with orientation along [0001]. Electro chemical detection is utilized for detection of Cortisol using anti- Cortisol antibodies (Anti-Cab) immobilized on ZnO nanostructures. The electrodes are characterized by using Scanning electron microscopy (SEM), Atomic force microscopy (AFM) and cyclic voltammetry (CV).
Electrochemical response studies of Anti-Cab/ZnO/ITO/PET immunoelectrode shows a linear relationship between the obtained current response and Cortisol concentration. The sensor exhibits a linearity from 1 pg/mL to 100 ng/mL, with a detection limit of 1 pg/mL and a sensitivity of 4µA/ (pg/mL) with a regression coefficient of 0.98. The obtained sensing performance is in physiological range. This developed sensor can be integrate with fluidic system for the automated sensing at point-of-care application

Over the past few years, a considerable effort has been spent on the development and optimization of organic polymers based memory elements. In this work we introduce an interesting approach consisting in the employment of a double gate dielectric - Organic Thin Film Transistor for the fabrication of high retention time, non volatile memory elements. The device structure consists in an aluminum gate electrode on which an ultrathin oxide layer, nominal thickness of 5 nm, is grown by means of UV-Ozone treatment. At the top of this structure, a second ultrathin insulating layer (thickness of 25 nm), made out of Parylene C, is deposited from vapor phase, and on top of it, metal source and drain electrodes have been patterned by means of photolithography or by inkjet printing. In all cases, TIPS-penatcene was employed as organic semiconductor. Thanks to the high capacitance coupling induced by the ultrathin double-layer insulating film, such devices can be operated at ultralow voltages, as low as 1V, showing mobility up to 0.4 cm2/Vs, Ion/Ioff up to 10^5 and remarkably low leakage currents (100 pA), with a typical breakdown field higher that 5MV/cm. Interestingly, we have found that by applying a pulsed gate voltage, possibly slightly higher than the nominal breakdown voltage, it is possible to induce a pronounced threshold voltage shift in the transistor behavior. In particular, we observed that the charges injected into the device channel are trapped into the Parylene C low-k dielectric (called electret), whereas, the Al2O3 high-k blocking dielectric avoid trapped charges to move all the way through the gate electrode.
It was found that, by applying a gate voltage pulse of -20V for 10 ms, usually gives rise to a threshold voltage shift higher than 1.5V in the same verse of the applied field. In other words, the device is strongly driven to its off state. We have observed a remarkably high Ion/Ioff ratio, usually in the range of 103, measured at -1V, and retention times higher than 105 s are typically obtained. We will demonstrate that by properly tuning the thicknesses of the two insulating layers and the program parameters (amplitude, duration and number of pulses) it is possible to dramatically increase the retention time up to 10^7 s.
Moreover, being all devices fabricated on a highly flexible (13 um thick) Kapton substrate, we will demonstrate that the final devices are characterized by a remarkable robustness to mechanical deformation. In particular we will show that the electrical performances of the fabricated OTFTs are not affected by a continuous mechanical deformation, and that the fabricated memory elements are able to retain the data even after more than 500 cycles at bending radii as small as 150 um.
The flexibility of the proposed structure and the simplicity of the employed fabrication procedure make this approach very interesting for practical applications.

Metal-reducing bacteria Geobacter sulfurreducens have been found to be able to transfer electrons to external electron acceptors (EEA) such as insoluble Fe(III) oxides, or anode electrodes in bioelectrochemical systems for electricity production, by either direct cell-EEA contact or the production of type IV pili as biological nanowires. The biological nanowires in G. sulfurreducens have been reported to be electrically conductive with and without bacteria cells and enable electron transfer from distant G. sulfurreducens cells in biofilm to electrodes.
However, up to now, the conducting mechanism of nanowires in G. sulfurreducens is still not clear. Previous scanning tunneling microscopy results did not find the evidence of cytochrome heme groups contributing to nanowires&’ conductivity. Denaturing cytochromes did not affect nanowire conductivity of G. sulfurreducens either. Although the protein sequence suggested less than 9% aromatic amino acids content in nanowire&’s protein pilin, PilA, X-ray diffraction patterns of purified nanowires surprisingly indicated tightly packed crystalline regions against amorphous background, leading to the guess of π-π interchain stacking between aromatic amino acids present in nanowires. In this presentation, we will show the characterization of the material properties of nanowires in G. sulfurreducens regarding their electric conductivity and elasticity under different conditions. Further exploration of their conducting features and the feasibility of using biological nanowires as conductive material will also be covered.

We have investigated M-DNA hydrogel gate graphene transistors utilizing water and hydrogel composition based on six M-DNA (M = Na, Mg, Ca, Fe and Zn). The capacitances for the water and M-DNA based hydrogels are almost same values at 20 Hz (~1.6mu;F/cm2), however, begin to change different value by increasing frequency. These results have shown that the smaller valence number lead to faster capacitive response with M-DNA hydrogel. Furthermore, capacitance behavior was observed by controlling concentration of Na-DNA. We have discovered three regimes in the capacitance vs. concentration of Na-DNA, and the each regime has different predominance, which rely on correlation between viscosity and capacitive response. Finally, the dynamic response for graphene transistors and inverter based on these M-DNA based materials is determined primarily by the change in the ON and OFF state, which in turn reflects the conductivity-frequency characteristic of the hydrogel dielectric and the device footprint. Future efforts to improve the switching frequency must focus on shrinking the device dimensions and on improving the capacitance-frequency and conductivity-frequency responses of the hydrogel materials.

Within the family of π-conjugated polyelectrolytes, there is great promise in cationic polythiophenes for the development of biosensors for genomic and proteomic applications, as for the detection of the amyloid fibrils formation or for the detection of Single-Nucleotide Polymorphism.[1] Recently, a series of DNA hybridization biosensors have been described, for which the cationic polythiophenes act as optical transducers through fluorescence properties.[2] However, is has been shown that the fluorescence signal of DNA hybridization biosensors is strongly dependent on DNA sequence, which affect the detection sensitivity and the homogeneity of the assays. So far, the lack of understanding in the DNA-CPT supramolecular assembly and hybridization processes constitute a strong limitation for applications in biosensors and bioelectronics.
Recently, we reported on the design of a series of cationic polythiophenes that assemble with DNA in hybrid chiral supramolecular complexes, for which the CPT helical assembly depend on the DNA sequence and topology.[3] In this work, we exploit these remarkable properties to probe the effects of DNA hybridization in DNA-CPT biosensor experiments in solution. Several important processes for the functioning of hybridization biosensors are examined, such as the formation of single-stranded DNA - CPT complexes, the hybridization of complementary DNA sequences, and the double-stranded DNA melting. By studying a series of complementary DNA probes, we reveal how the self-assembly is influenced by the DNA sequence, topology, and stability. Moreover, by means of a joint experimental/theoretical approach, we give important clues on the conformational changes and DNA-CPT binding mechanisms, which are important for achieving a rational design of biosensors.
[1] Hammarström, P.; Simon, R.; Nystrom, S.; Konradsson, P.; Aslund, A.; Nilsson, K. P. Biochemistry 2010, 49, 6838 ; Gaylord, B. S.; Massie, M. R.; Feinstein, S. C.; Bazan, G. C. Proc. Natl. Acad. Sci. U. S. A. 2005, 102, 34.
[2] Ho, H.-A., A. Najari, M. Leclerc, Acc. Chem. Res. 2008, 41, 168. Charlebois, I.; Gravel, C.; Arrad, N.; Boissinot, M.; Bergeron, M. G.; Leclerc, M. Macromol. Biosci. 2013, 13, 717.
[3] Rubio-Magnieto, J.; Thomas, A.; Richeter, S.; Mehdi, A. ; Dubois, P.; Lazzaroni, R.; Clément, S.; Surin, M. Chem. Commun. 2013, 49, 5483.

Bioelectronics field demands the development of new materials that have a tendency to combine the features of organic with that of inorganic materials. One of outlook candidates for that purpose is glycine - the simplest amino acid and one of the basic and important elements in biology as it serves as building block for proteins. It is known that glycine has three polymorphic forms with different physical properties, but more perspectives are polar γ- and β- phases with hexagonal (P3₂) and monoclinic (P2₁) non-centrosymmetric space groups respectively. The minor differences in space group and angle between COO_ and NH3₊ functional group cause γ- phase are more stable and attractive for applications than β- phases. But the situation is changed when recently the interest in β- phase glycine has arisen from its useful functional properties such high value of the nonlinear optical susceptibility and ferroelectricity including possibility to ferroelectric switching domains.
In this work we present the growth of stable β phase glycine microcrystals with clear crystallographic habitus grown on Pt/SiO₂/Si substrates. The influence of various parameters (e.g. concentration of solution, solvent, volume of microdroplets, temperature, humidity) on the formation of polymorph phases was evaluated using X-ray diffraction analysis and Raman spectroscopy. We have established that β- polymorph has strong interaction with a light beam. The high value of the optical susceptibility (greater than that in γ-phase glycine with reference to the z-cut quartz) was confirmed by means of nonlinear optical second harmonic generation method (SHG). Additionally, the evidence of ferroelectric properties was confirmed by means of Piezoresponse Force Microscopy (PFM) where the piezoelectric response and ferroelectric switching domains of the β- glycine have been investigated. The value of electromechanical coupling in bio-organic β- glycine has been revisited and this property was found to be sufficient for micromechanical applications.
The major part of this work was supported by the Marie-Curie ITN project “Nanomotion” (grant agreement no. 290158).

We have demonstrated proton-conducting transistors using palladium hydride as a proton-injecting contact. Palladium absorbs hydrogen gas, forming palladium hydride (PdHx), with x varying from 0 to 0.7 depending on the concentration of hydrogen present. When a bias is applied, the PdHx contacts can inject protons into a proton-conducting material. Here, I present an in-depth characterization of the proton-injection characteristics of the PdHx contacts. Time-resolved electrical measurements and micro-scale four-point probe measurements are discussed. The effects of proton concentration in the contacts on the contact protochemical potential and diffusion coefficient are measured, along with the differences between the material&’s alpha (xasymp;0.1) and beta (xasymp;0.7) phases. The results of these measurements are compared with a finite-element simulation of the contacts, which considers the changes in both conductivity and charge carrier concentration.

Conducting polymers have the potential to be widely used in biomedical applications due to their biocompatibility and inherent conductivity. More specifically, conducting polymers are well suited to be used as artificial muscles because they can operate as electromechanical actuators in biological fluids under low applied voltages. However, the material properties limit their use as artificial muscles because the conjugated backbone of conducting polymers makes the bulk materials brittle, and ion mobility through the polymers is low. Here we present the synthesis and characterization of new copolymers containing flexible oligoether linker units of varying length in the polymer backbone aimed at improving both the mechanical properties and the ionic conductivity of thiophene-based conducting polymers. Furthermore, we have developed a method to crosslink PEDOT-OH to make the material more robust. The copolymers were characterized using FTIR, CV, 4-point probe resistivity measurements, film morphology was evaluated with SEM, and mechanical properties were evaluated using a dynamic mechanical analyzer. Preliminary actuation experiments will also be presented.

Dopant-functionalized anilines with improved electrocatalytic properties are promising building blocks for the construction of bioelectronic devices [1]. The present study is devoted to the use of polyanillines possessing different substitution patterns in the interaction with the enzyme PQQ-GDH, which is advantageous in biosensor engineering [2] as well as in the construction of biofuel cells [3]. The aim is to obtain an electron transfer from the substrate reduced enzyme to the polymer without additional shuttle molecules. This has been first studied in solution and then transferred to a surface in order to build a reagentless enzyme electrode. 6 polymers have been prepared from different mixtures of sulfoxy-, methoxy- and carboxy-substituted aniline by chemical synthesis and characterized by UV/VIS, IR and NMR spectroscopy. It is shown that 4 polymers containing carboxy-modifications at the aniline ring are in the pernigraniline state after synthesis, whereas polymers substituted only by sulfoxy- and methoxy- groups appear in the emeraldine state. The different redox state clearly influences the reaction with the enzyme in solution: only the latter polymers can be reduced by the enzymatic reaction. pH dependence of the reduction indicates that the behaviour is dominated by the enzyme activity. The reaction can also be verified electrochemically with two polymers (sulfoxy- and methoxy-modifications only) showing that electrons can not only be transferred from the enzyme to the polymer, but further towards an electrode surface. In a next step the polymers have been immobilized as thin films on the electrode and the enzyme has been coupled to these films. Under these conditions it can be shown that the electrode potential can appear as a valuable driving force for direct electron transfer even for polymers which are not reacting in solution [4]. Thus, these results can be considered as a further step towards the better understanding of the roles played by the structure and interface of polymers in their interaction with biomolecules.
[1] Wallace GG, Kane-Maguire LAP. Manipulating and monitoring biomolecular interactions with conducting electroactive polymers. Adv Mater 511 2002;14:953-60
.
[2] Durand F, Stines-Chaumeil C, Flexer V, Andre I, Mano N. Designing a highly active soluble PQQ-glucose dehydrogenase for efficient glucose biosensors and biofuel cells. Biochem Biophys Res Commun. 2010;402: 750-4.
[3] Schubart IW, Göbel G, Lisdat F. A pyrroloquinolinequinone-dependent glucose dehydrogenase (PQQ-GDH)-electrode with direct electron transfer based on polyaniline modified carbon nanotubes for biofuel cell application. Electrochim Acta 2012;82:224-32.
[4] Sarauli D et al. Differently substituted sulfonated polyanilines: The role of polymer compositions
in electron transfer with pyrroloquinoline quinone-dependent glucose dehydrogenase Acta Biomater 2013; 9: 8290-8298

Charge transport in double stranded DNA (dsDNA) molecules has been intensively investigated over the past two decades. Various experimental techniques and theoretical approaches have been used to understand charge transport in dsDNA. However, little is known about charge transport though mixed oligomers such as DNA:RNA duplexes. DNA:RNA hybrids are important biological components and are integral to the processes of DNA replication, transcription and reverse transcription. However, these hybrid oligonucleotide pairs have significant changes in structure compared to dsDNA. As such, the charge transport properties of DNA:RNA hybrids are expected to be substantially different than dsDNA. In this work, the conductance of individual DNA:RNA hybrids is measured, and we systematically study the transport properties of these systems by changing both the length and sequence of the hybrid pair and comparing these results to the equivalent dsDNA duplexes to obtain fundamental insight into the conductance properties of these important biological systems.
In this work, the conductance of the oligonucleotide duplexes is directly measured using the Scanning Tunneling Microscope (STM)—break junction technique in aqueous solution. This approach, which has previously been used to obtain reproducible conductance values for dsDNA has been adopted to directly measure individual DNA:RNA hybrid duplexes by linking them in between the tip and substrate in an STM. With this setup, thousands of individual conductance measurements can be obtained rapidly for statistical analysis, thus allowing the most probable conductance of a single molecule to be determined. In this work, measurements of various number of G:C or A:T/U base pairs provide us a better understanding of the fundamental charge transport mechanisms in DNA:RNA hybrids.

Combinations of an ISFET with a reference field-effect transistor (REFET) have been reported in the past by many researchers. In conventional ISFET/REFET pairs, the ISFET is sensitive to pH and by covering the gate oxide with a polymeric layer an REFET with zero sensitivity to pH is achieved . This work is dedicated to integration of the same concept to a silicon nanowire (SiNW) FET sensor. The new nanowire/microfluidic channel combination is covered with an alkoxysilane monolayer which offers minimized pH and ion sensitivity conditions as required previously for the REFETs.
The SiNW FET in our work consists of both sensor (SENW) and reference nanowire (RENW) sets with identical electrical properties. The purpose of the first integrated reference set is to eliminate disturbances in the signal caused by the nanowire/background electrolyte interface and the second set enables us to differentiate the specific binding of target molecules from nonspecific interactions. In order to verify the feasibility of such reference sets, their oxide surface should be modified such that they are chemically inert to the molecular species under detection. As a result, the oxide surface of all the silicon nanowires in the sensor chip was first covered with 3-aminopropyltriethoxysilane (APTES) film through microwave-assisted silanization in anhydrous toluene at 75°C for various silanization times. The APTES films were characterized using ellipsometry, Atomic force microscopy (AFM) and attenuated total reflection (ATR) mode of Fourier transform infrared (FTIR) spectroscopy. Surface characterization results suggest that microwave-assisted silanization for 10 minutes produces a continuous and uniform monolayer of APTES on the nanowire surface. Electrical measurements on the silanized SiNW FET in buffer solution reveal that the produced APTES monolayer successfully passivates the surface silanol groups and compared to bare silicon oxide surface, the response to ion or change in concentration is minimized.
Furthermore, single-stranded DNA probes were attached to the silanized surface of the nanowires and the adopted functionalization strategy was investigated through hybridization with a fluorophore-tagged complementary DNA strand (also referred to as target DNA). The results show that the APTES monolayer can be chemically modified if desired for biosensing.
The results of these investigations have led to the design of a SENW/RENW FET which is optimized for sensing target biomolecules or change in pH of a solution measured as a differential current referenced to silanized and/or bio-functionalized nanowire sets integrated on the chip.

This project demonstrates the development of a zinc oxide (ZnO) based microelectrode sensor for the ultra-sensitive detection of protein biomarkers. Biomarkers are unique biological macromolecules that may indicate the presence or risk of certain developing ailments. Point-of-care, rapid quantification of these molecules is essential to disease identification, monitoring, and analysis. Currently employed technologies for quantitative detection of protein biomarkers suffer from problems such as a lack of sensitivity/selectivity, dominance of signal noise, adaptability of detection to a wide range of biomolecules, and are not geared for rapid detection. Our research focuses on utilizing a materials-based approach to overcome these problems often associated with the detection of biomarkers by utilizing ZnO as part of our biosensor for (1) improved binding surface area for enhancing sensitivity and (2) creating nanostructures for biomolecule confinement that can enhance output signal response. This study integrated nanotextured ZnO thin films onto printed circuit boards using RF magnetron sputter deposition at room temperature. By manipulating ZnO deposition conditions, certain properties of the material can be tuned to increase the efficacy of signal transduction. These fabrication conditions not only dictate the number of oxygen vacancies within the film but also regulate the amount of zinc and oxygen terminated ends occurring on the material surface.
This study focuses on the correlation between the effect of physical confinement and surface termination of nanotextured ZnO to its performance as a biosensor. ZnO films sputtered with and without the presence of oxygen were examined for possible differences in biosensor efficacy. Two cross-linker molecules, dithiobis succinimidyl propionate and (3-aminopropyl)triethoxysilane, were evaluated for their ability to bind to these two different surfaces using fluorescent studies. Qualitative and quantitative assessment of cross-linker binding was accomplished using microscopy and fluorescent intensity measurements. Impedance spectroscopy (EIS) was used as the electrical transduction mechanism for detection of the well-established cardiac biomarker, troponin-T, whose presence in trace quantities is indicative of multiple cardiovascular ailments. Utilizing EIS with a functionalized immunoassay on the ZnO surface, troponin-T was detected as low as 10 fg/mL in purified buffer media as well as in human serum. The enhanced detection of the cardiac biomarker using ZnO films sputtered without oxygen can be directly attributed to 1) oxyge