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
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[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) oxygen vacancies within the metal oxide film, 2) the nanotexturing of the sensing site surface, and 3) the ability to bind a significant amount of cross-linker molecules for immobilizing capture antibodies. This platform demonstrates applicability as a sensitive, low-cost, rapid and easy to use tool that can be integrated as a point-of-care diagnostic device.

Iontophoresis is a one of methods to enhance the drug penetration across the skin via ion movement under electrical potential known as transdermal drug delivery system (TDDS). In this work, calcium-alginate (Ca-Alg) hydrogel was used as a matrix, which was prepared by solution casting using CaCl2 as a crosslinker. Benzoic acid (BA) is an anionic drug which was used to study the release mechanism and the diffusion coefficient. The diffusion coefficients increase with decreasing crosslinking ratio due to larger mesh size of hydrogel. The diffusion coefficient is shown to be controlled by applied electric field strength and electrode polarity. The release behavior is further developed by using poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticle as the conductive polymer as the drug substrate and blended with a Ca-alg hydrogel. The PEDOT nanoparticle was synthesized via the chemical oxidation polymerization at various oxidant and surfactant concentrations. Variously distinct particle shapes were obtained: irregular, raspberry agglomerate, coralliform, orange-peel, globular, and plum shape. The particle sizes and the electrical conductivity values were in the range of 60 nm to 900 nm and < 1 S/cm to 153 S/cm, respectively, depending on the polymerization condition. Due to the various and distinct PEDOT nanoparticle sizes and morphologies, they are expected to extend the operation window of TDDS.

Biosensors have been developed widely in the medical and the human healthcare sectors for many years since the biosensors provide attractive options such like the cost-effectiveness, the good sensitivity and the rapid response times. Especially portable biosensor systems based on Si based transistor for the rapid detection of specific biomolecules are crucial for anti-bioterrorism, disease diagnostics, and food safety. However, the rigid and the opaque characteristics of the Si wafer induce some difficulties to apply it to flexible skin or to detect anti-body reaction by microscope in transmittance mode.
Here, we demonstrated high sensitive and high transparent amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs) employing indium-gallium-zinc oxide (IZO) as the source and the drain electrodes for biosensor applications. The device performance shows a high field effect mobility of ~ 6 cm²/Vs, a subthreshold slope of 650 mV/decade, drain current on-off ratio of ~ 10⁶ with high transparency over 80%. To store the culturing media, we also achieved 2-step reservoir structure with SU-8 polymer on TFTs. The bio-sensing effect of the IGZO TFT design has been studied using bacteria of thermococcus gammatolerans and olfactory receptor neurons. The thermococcus gammatolerans and the olfactory receptor neurons from rat nerve cells are well cultured on the IGZO junction layer or the insulator surface for passivation. The reaction of the bacteria or the specific odorant molecules with a-IGZO TFTs can be detected in real time with high signal ratio. The characteristics of oxide TFTs-based sensors can be optimized by simple surface engineering. Furthermore, IGZO-based TFTs can operate in aqueous electrolytes that are essential for real-time chemical and biological sensing applications. The low process temperature of IGZO TFTs can give an important merit to use flexible substrate. Therefore, the IGZO TFT-based biosensor satisfies important requirements, such as high sensitivity, transparency, disposability, high throughput sensing and application as flexible biosensor.

Microtubules are a subset of cytoskeletal eukaryotic proteins. Their role has been proposed by different groups in memory retentions with feasible ionotropic or metabotropic mecahnisms, pertaining to electrical charge transfer process. Tuszynski and group have proposed that microtubules behave as ferroelectric materials and have given a detailed theoretical justification for the same. We've used microtubules together with microtubule-associated proteins, that are meant to give them structural stability, further known as MAPs-rich microtubules.
Following up, we did two separate studies for the electrical characterization, namely, electrostatic force microscopy (EFM) and polarization-voltage (P-V) measurements. The samples were prepared on n+ Silicon (resistivity- 0.05 ohm-cm) and PET sheets with two planar Cr-Au (50 nm: 5 nm Cr + 45 nm Au) electrodes deposited by metal evaporation process, for EFM and P-V measurements respectively. Liquid MAPs-rich microtubules (~0.1 mg/ml) was drop-casted on the substrate and further spinning was done for uniform coverage of the protein sample on Si and between the electrodes.
There was no colour reversal (from light-to-dark and vice versa) upon reversing the applied voltage bias in EFM; a loop with no saturation plateau (likening to that of a banana) in P-V measurement was observed. Hence, we observed a chargeable dielectric behaviour in both the characterizations.

Bottom-up assembly, which enables construction of complex architectures from molecular building blocks, is a promising alternative for the fabrication of future electronic devices. DNA and, in particular, DNA origami have made possible the fabrication of complex, self-assembled, molecularly addressable, nanostructured templates. This paper describes the results of our efforts to selectively deposit two different metals on the same DNA origami template as a step towards the fabrication of complete nanoelectronic circuits. The deposition of copper and gold onto pre-designated locations on the template, as verified by both compositional and morphological data, was accomplished to form a heterogeneous Cu-Au junction. Seeding and deposition were performed in sequential steps. An enabling aspect of this work was the use of an organic layer or “chemical mask” to prevent unwanted deposition during deposition of the second metal. The approach demonstrated in this work can be used for site-specific deposition of a much broader set of materials like semiconductors, which are required for circuit fabrication on DNA templates. Continuing efforts seek to optimize the yield, morphology, and electronic properties of multiple metals deposited on DNA origami templates.

DNA is one of the most fascinating materials used in nanoscience today. First, it is a promising molecule for applications in molecular electronics. It was noticed early that the structure of double-stranded DNA (dsDNA) provides a pi-stacking structure that could potentially lead to efficient conduction along the chain. Secondly, DNA has self-assembly properties, and recent advances in DNA origami have demonstrated its utility for creating nanostructured. These properties suggest that it may be possible to design hybrid DNA-based materials with tunable electrical properties. Moreover, DNA is currently used in the diagnosis of many diseases. A clear picture of the electrical conductivity of this molecule could open the doors for the design of diagnostic tools that could be read electronically; improving the sensitivity and reducing costs.
Although results of DNA conductance reported in the literature span a huge range and differ by orders of magnitude, some consensus has been achieved in the charge transport mechanism, being found to be tunneling in short molecules (less than 4bp) and hopping in longer DNA molecules. Besides length, other factors influence DNA conductance. Sequence can modulate conductance, as some bases participate in the charge transport process. The presence of single nucleotide polymorphisms (SNP) has been reported to modulate conductance as well. But, to date, conductance modulation by structure in different DNA forms has not been studied. The B-form typical for dsDNA is a right-handed double helix with an average distance of 0.33 nm per base pair and it has been extensively studied. The A-form is the prototypical structure for dsRNA, but can be induced in dsDNA by dehydration. It is a right-handed helix with a shorter rise per base pair than the B-form (0.23nm/bp).
Herein we report conductance measurements of amino-functionalized short dsDNA molecules using the STM-break junction method. Briefly, a gold STM tip is brought into contact with a gold electrode and then retracted with the molecule present in solution while the current between the electrodes is recorded. This process is repeated thousands of times and results can be used to obtain conductance histograms. We study dsDNA conductance as function of length, sequence and structure. The structure is changed from B-form to A-form by adding ethanol during the experiment.
Results demonstrate that A-form dsDNA is ~10 times more conductive than B-form in GC rich sequences. These results help to rationalize the divergence in conductance results reported in the literature and pave the way for the design of nanodevices based on DNA with tunable structural and electrical properties and sensors that could take profit of this conductance-structure modulation

Emulation of human touch sense via electronic means is of pivotal importance for developing intelligently accessible and natural interfaces between human/environment and machine, which necessitates the development of large-scale pressure sensors array with high spatial-resolution, high-sensitivity and fast response. Using the piezoelectric polarization charges created at metal-semiconductor interface under strain to modulate transport of local charge carriers, piezotronic effect has been applied to design 3D array of independently addressable strain-gated vertical piezotronic transistors (SGVPT) based on vertically aligned ZnO nanowires (NWs), which convert mechanical stimuli applied on the devices into local electronic controlling signals. By combining the patterned in-place bottom-up synthesis of vertically aligned ZnO NWs with state-of-the-art microfabrication, macro-scale integration of SGVPT array with taxel density of 92 × 92 in 1 cm2 has been achieved and parallel manufacturing of SGVPT arrays on 4-inch PET flexible substrates has been presented. The taxel area density of SGVPT array is 8464/cm2, not only enabling a 15-to-25-fold increase in number of taxels and 300-to-1000-fold increase in taxel area density compared to recent reports (~ 6-27/cm2), but also much larger than the number of mechanoreceptors embedded in the human fingertip skins (~ 240/cm2). The fabricated sensors are capable of mapping spatial profiles of small pressure changes (< 10 kPa).
The reliability and stability of device operations have been probed, exhibiting a good stability of SGVPT array operation for future applications like in vivo physiological sensing in complex environments for certain designed time of period. The feasibility of SGVPT array for applications such as self-powered active and adaptive artificial skin has been presented by converting mechanical stimulations into electrical signals without external bias, which emulates the physiological operations of mechanoreceptors in biological entities. This enables real time detection of the device shape change and feeding-back the sensed changes in shape for calibration of other functionalities as well as corresponding control/response performed by the system, which is a desirable feature for sensors embedded in an artificial tissue or prosthetic device. The scalability of this technology in integrating in-place synthesized single-crystalline NWs in controllable manners together with its demonstrated compatibility with state-of-the-art microfabrication techniques enables future implementation of nanomaterials for practical applications in smart skin, prosthetics and novel surgical instruments.
Ref: Wu W. Z.*, Wen X. N.*, Wang Z. L. Taxel-addressable matrix of vertical-nanowire piezotronic transistors for active and adaptive tactile imaging. Science 340, 952-957, 2013. *Authors with equal contributions

Human pulse, an essential indicator of health conditions, can be found at any point on the body where an artery's pulsation is transmitted to the surface. Here we introduce a cost-effective and highly sensitive flexible accelerometer, which can sense human pulse by detecting the pulsation. Conventionally, accelerometers are fabricated by expensive micro fabrication techniques with rigid substrates like silicon or silicon nitride. In contrast, this work employed a facile fabrication method to generate flexible light-weight accelerometers by direct-printing of silver nano-inks on pre-patterned flexible paper substrates. The accelerometer employs capacitive sensing with a structure of two parallel plate electrodes with the optimally designed top electrode pattern in order to achieve high sensitivity. A double-bridged membrane type top electrode and a simple bottom electrode are defined in pre-patterned paper via spraying of silver nano-inks, followed by thermal annealing at 160 degree celsius. Finally, a readout circuit is designed and integrated with the accelerometers by thin wires to convert capacitance changes to a voltage change signal. When the accelerometer is attached to the body surfaces: neck, inner elbow, or any other pulsation point, a continuous pulse wave is obtained which shows accurate pulse rate and amplitude by reading out the voltage output signal.
Reference
Y. Zhang, T. Lei, and W.S. Kim*, “Design-optimized Membrane-based Flexible Paper Accelerometer with Silver Nano Ink” Applied Physics Letters 103, pp.073304 (2013).

Recording neural electrodes capture the electrical activity generated by neurons. To obtain long-term reliable signals, the electrode must be biocompatible, and have stable electrical properties; micro-size electrodes are needed in order to have higher spatial selectivity. As the electrode size goes down, initial electrode impedance increases and therefore, sensitivity and quality of signal decreases. Hence, several strategies have been conducted to modulate a tradeoff between the size (spatial selectivity) and quality of signal recordings (sensitivity) in neural electrodes. However still having devices with sufficient electrical properties is a challenge. Bioelectric signals in physiological environments are in the form of ionic currents. In order to process these biological signals, neural electrode transduces them to the electronic from. Conducting polymers (CPs) have been extensively used for biomedical applications; in particular, for neural interfaces due to their unique characteristics, such as biocompatibility, both ionic and electrical conductivity and response to electrical stimulation.
Here we report a novel method for fabrication of conducting polymer microspherical cups (CPMSCs) for improvement of electrical properties and on-demand drug release. The fabrication process involves electrospraying of biodegradable poly (lactic-co-glycolic acid) (PLGA) microspheres on a gold substrate, followed by electrochemical polymerization of conductive polymers poly (3,4-ethylenedioxythiophene) (PEDOT) on the gold substrate and around the PLGA microspheres. We can control the diameter of the PLGA microspheres by controlling the electrospraying parameters such as polymer concentration, flow rate and voltage. The diameters of the microspheres range from 3±2mu;m, and wall thickness of the PEDOT spherical cups varies from 50-100nm. By changing the polymerization time, we can reproducibly control the opening size of the CPMSCs and create either fully coated PEDOT (sphere) or partially coated PEDOT (spherical cup). Fabrication of CPMSCs on the surface of electrodes will provide an extremely low impedance and high charge transfer capacity recording electrode due to extremely high effective surface area of CPs. These results demonstrate superiority of CPMSCs for neural recordings and stimulations whereas the low-impedance electrode tissue interface is essential.
As future study we envision the extension of the CPMSC system reported here as a controlled drug delivery system by incorporation anti-neoplastic agents during electrospraying process. We anticipate that drug can be released from CPMSCs in a controlled fashion by actuation of CP during electrical stimulation (~1V). This system holds considerable promise for simultaneously detection and targeted and controlled release systems. By employing a targeted release method, drug release rate can be tailored to the need of a specific application, while reducing side effects and improving patient compliance.

An increasing number of visceral organs and associated disease conditions have been demonstrated to be under neural control. Precision electrical modulation of neural signalling patterns has the potential to provide therapeutic benefit in a host of chronic diseases such as diabetes, asthma, hypertension, arthritis and even cancer. The bioengineering demands of creating “bioelectronics medicines” centred on neural interfaces are considerable. Such devices require advanced geometries and materials, which will enable miniaturized electrodes to interface with peripheral nerves anywhere in the viscera. The interfaces must be compliant and malleable to conform to visceral nerve anatomies including plexi, and have high-density geometries able to target specific fibre subsets including fascicles. Ideally, they would be able to perform controlled nerve re-configuration, re-shaping, or opening to limit the long-term penetration damage and must have a high signal to noise ratio which should experience minimal change over a period of several months. Spatial resolution should target single axon level interrogation and may require conductive materials and coatings to improve charge injection density. Implantable device electronics should be able to read and write the full complexity of the signalling pattern within the nerve; and smart enough to operate in a closed loop fashion, regulating organ function in response to therapeutic signatures. This presentation will outline research efforts and several funding opportunities being provided by GSK for the development of such neural interfaces.

In electronic circuits as well as in the cell systems of mammalians signals are processed, amplified and distributed utilising complex pathways and various discrete components. In electronics, those are represented by electrically conducting networks, resistors, diodes and transistors. In biology, nerves and the vascular network together with the axons, glands, the synaptic terminals etc represent the circuit system. Here, we report ionic conductors, resistors, diodes and transistors that together represent a chemical circuit technology that enable translation of electronic addressing signals into delivery of complex chemical signals and gradients. The chemical circuit technology is built up from solid-state anionic and cationic polyelectrolytes combined with conjugated polymers. We report the characteristics of ionic resistors and conductors together with the principle of operation of ion bipolar junction transistors and diodes. Further, an array of different chemical circuit systems has been built, aiming for complex regulation of biology, at high chemical and spatiotemporal resolution. The performance and application of those circuits in cell biology and therapy experiments are reported, as well.

Bioelectronic medicine has numerous promising applications for the treatment of diseases and disorders of the nervous system, but also many challenges. Two of the key limiting factors to the development of next-generation neural interfaces are the low charge transfer area and poor neural tissue integration of conventional metallic electrodes [1, 2]. The “synaptic electrode" concept draws upon knowledge from both implantable neurostimulator and bioelectrode research, and combines it with the principles of tissue engineering. The basis of this technology is a conductive hydrogel (CH) which provides a new approach to tailoring the neural interface by decreasing the strain mismatch while providing a conductive path within a soft, deformable hydrogel matrix [3]. A typical CH consists of a biosynthetic hydrogel integrated with a CP, such as poly(ethylene dioxythiophene) (PEDOT). The hydrogel is a co-polymer of poly(vinyl alcohol) (PVA) and a modified biological molecule. Varying the type of biomolecule has allowed the properties of the CH to be tailored such that specific cells will interact with the electrode coating. CH efficacy and safety has been demonstrated in vivo, with reduced scar tissue compared to conventional platinum interfaces. The “synaptic electrode” construct is produced by the addition of a degradable PVA layer overlying the CH, in which cells can be encapsulated. This hydrogel layer provides both the ability to encapsulate cells within the electrode and simultaneously deliver therapeutic agents to promote regeneration or directed growth of neurons. Specifically, co-cultures of neurons and supporting glia have been embedded in the electrode coating, and found to survive and differentiate to produce active neural processes. The neural networks grown within the hydrogel matrix are excitable at lower thresholds than typical neural tissue at the implant interface. It is expected that integration of this bioelectrode into neural tissue will create a “synaptic electrode” to directly interact with excitable target tissue. These studies provide evidence that next-generation electrode arrays can be developed to safely deliver stimulus and accurately record from high density electrode arrays using natural synaptic processes. These bioactive neural interfaces create a technology platform which can be tailored for bioelectronic applications such as functional electrical stimulation (FES), nerve guides, bionic ear and eye devices and deep brain stimulators.
References
1. Ludwig, K.A., et al., Chronic neural recordings using silicon microelectrode arrays electrochemically deposited with poly(3,4-ethylenedioxythiophene) (PEDOT) film. J Neural Eng, 2006. 3: p. 59-70.
2. Green, R.A., et al., Conducting polymers for neural interfaces: Challenges in developing an effective long-term implant. Biomaterials, 2008. 29: p. 3393-9.
3. Green, R.A., et al., Conductive hydrogels: Mechanically robust hybrids for use as biomaterials. Macromol Biosci, 2012. 12.

Biocompatible materials capable of conducting electricity have numerous biomedical applications including use as electrodes for neurological stimulation and recording, tissue engineering, artificial muscles, and stimuli-responsive actuators or sensors. Therefore, we are developing new ‘soft&’, flexible, polymer-based electrode materials that can be integrated into biological tissues with minimal damage to the host. To this end, we have synthesized composite materials composed of the polypeptide silk fibroin (for mechanical strength, flexibility, biocompatibility) and poly(pyrrole) or poly(3,4-ethylenedioxythiophene) (conducting polymers for electrical interfacing). Covalent attachment of negatively charged, hydrophilic sulfonic acid groups to the silk protein can selectively promote pyrrole absorption and polymerization within the modified films to form a conductive, interpenetrating network of polypyrrole and silk that is incapable of delamination. Using this strategy, we are able to produce silk-based ‘electrodes&’ with various architectures including fibers, 2D films, 3D porous sponges and hydrogels. In addition, we have found that specially designed silk-polypyrrole composites can function as electromechanical bending actuators, which show immense promise for the development of implantable valves or drug delivery devices.

Nanostructured forms of carbon have extraordinary mechanical and electrical properties.
The fact that carbon is considered inherently biocompatible means that these more recently discovered forms have attracted the attention of those of us interested in the development of more effective electromaterials for medical bionics.
A number of different carbon nanotube based electromaterial platforms have been shown to provide effective electrical communication with both nerve and muscle cells. These advances will be presented here.
More recently a structure consisting of graphene layers deposited on a biopolymer substrate has proven to be effective in nerve cell communication. A striking feature of this electrode structure is that the very thein layer of (bilayer) graphene used has minimal effective on the mechanical properties of the underlying biopolymer yet provides sufficient electronic conductivity for electrical stimulation of nerve cells.

Nerve defect in both central and peripheral nervous system is a major health problem. Spontaneous axonal regeneration is only applicable to small lesions within the injured peripheral nervous system and is suppressed within the central nervous system. Axons can be guided along specific pathways by gradients of attractive and repulsive chemical and physical cues. However, the molecular mechanism of action of such gradients is poorly understood. To understand the effect of gradients of guidance cues individually or in combination on growth cone turning and growth rate modulation, the development of platforms that are capable of producing precisely controlled shape gradients of different guidance cues is essential. Conducting polymers have been widely reported in biomedical field especially for drug delivery systems and neural interfaces. Conducting polymers have the ability to response to electrochemical redox reaction by changing their color, conductivity, wettability, and volume. Previously we developed a novel method for fabrication of randomly oriented conducting polymer nanotubes for controlled release of an anti-inflammatory drug. We hypothesize that the aligned conducting polymer nanotubes will provide both physical and chemical guidance cues for axonal regeneration.
Here we report a novel method for fabrication of multifunctional aligned conducting polymer nanotubes for axonal regeneration. We successfully incorporated nerve growth factor (NGF) into poly (3, 4-ethylenedioxythiophene) (PEDOT) nanotubes using a templaing method. Electrochemical deposition of PEDOT was carried out by an applied current density of 0.5 mA/cm2. We characterized surface morphology and electrical properties of the NGF-loaded PEDOT nanotubes by using scanning electron microscopy and impedance spectroscopy, respectively. The diameter and wall thickness of PEDOT nanotubes were 100 ± 23 nm and 30 ± 5 nm, respectively. The impedance of substrates decreased about two orders of magnitudes after electrodeposition of PEDOT nanotubes. In order to release the NGF from PEDOT nanotubes in a controlled fashion, we actuated PEDOT nanotubes by applying a bias voltage 1 V for 5 times at three specific time points of 170, 360, and 600 hr. Preliminary results showed that NGF was precisely release (~65ng/ml) from PEDOT nanotubes after electrical actuation. To evaluate the biocompatibility of aligned PEDOT nanotubes, primary dorsal root ganglion (DRG) explants and PC12 cells from rats were cultured on the substrates. PEDOT nanotubes supported neurite outgrowth from the ganglia in the direction of the nanotubes In Future, we will design a multifunctional conduit using aligned PEDOT-NGF nanotubes and we will examine the rate of axonal regeneration nerve gap in rats.

Organic electrochemical transistors (OECTs) have been targeted for a variety of in vitro and in vivo diagnostic applications owing largely to their efficient transduction of ionic to electronic signals. In these devices, the transistor drain current is modulated by de-doping of the PEDOT:PSS {poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate)} channel due to local variations of ion flux induced by, for example, neural activity. Owing to the efficient ion mobility and high capacitance in hydrated PEDOT:PSS, we are able to fabricate devices with high intrinsic amplification (transconductance), and when scaled to micron dimensions, broad-band response up to 10 kHz. Along with facile and robust/conformal fabrication schemes, these devices show great promise for a number of neuroscience applications. By studying film morphology and by systematically varying OECT device geometry, we develop a fundamental understanding of device operation and establish design rules for practical implementation of OECTs in vitro and in vivo, for both research and clinical applications. Considering the recording capabilities of common measurement techniques, and the nature (amplitude, frequency) of neural signals, we describe how a tradeoff between OECT device response time and transconductance can be navigated. With this scheme, we demonstrate the use of OECTs to record low amplitude, low frequency neural oscillations, high amplitude epileptiform activity, and show that measurements of individual action potentials are within reach. Thus, these devices can be tailored for various applications depending on the desired or required content of neural signals.

The long-term performance of introcortical neural probes is often complicated by a foreign body reaction that consists of accumulation of microglia, neuronal apoptosis and an insulating glial sheath around the implants. This extensive gliosis has been associated with the system impedance increase and signal deterioration and loss of the devices. Previously we have proposed that the in vivo polymerization of a conducting polymer, poly (3,4 ethylene dioxythiophene) (PEDOT), in living tissue may help to build a conducting pathway between the retreated neurons and the probe. The EDOT monomer can be infused into the tissue with a microcannula/electrode guide followed by electrochemical polymerization under the oxidative current through the electrodes. Here we examined the effects of this in vivo method by polymerizing PEDOT in living rat hippocampus at different time points post initial device implantation. We found that the system impedance was decreased for all the groups regardless of scarring stage. However, there seemed to be an optimal time window for sustained impedance improvement. The tissue responses to the polymer were examined with immunohistology. We also investigated the effects of polymerization on local neural function with a hippocampus-dependent behavior test, delayed alternation (DA). Compared to the control groups, in vivo polymerization did not cause significant deficit on the hippocampal function.

Advances in bioelectronics require materials that facilitate the interface between biological systems and electronic materials. Unfortunately, many of the challenges involved in achieving and maintaining functional bioelectronic interfaces result from a relative lack of materials that are both soft and electrically conductive. Electronic materials are generally inelastic and extremely brittle, while hydrogels, which have mechanical properties that closely mimic a diverse range of tissues types, are electronic insulators. Although there are reports of electroactive hydrogels created by chemically conjugating conductive polymers (e.g. polypyrrole, polyanaline) to hyaluronic acid (HA) or polyethylene glycol (PEG), the ideal bioelectronic interface would be formed of materials that are endogenous to the anatomical area of interest.
To this end, we have synthesized an electroactive composite material for neural tissue engineering and bioelectronics by chemically conjugating hyaluronic acid (HA) and dopamine (DA). Hyaluronic acid is an endogenous polysaccharide whose properties as a hydrogel have been well-characterized. This versatile material is found in the mammalian brain, and has been used as a protective interface to prevent glial cell adhesion and as a scaffold to selectively direct the differentiation of dopaminergic neural progenitor cells (dNPCs). Dopamine is an essential neurotransmitter, and neural melanin is composed of dopamine that is produced by dopaminergic neurons located in the mammalian ventral midbrain. These neurons play a significant role in the clinical manifestations of Parkinson&’s disease and schizophrenia, and ex vivo cultures of dopaminergic neurons have shown promise as a cell therapy for Parkinson&’s patients. However, dopaminergic neurons are difficult to cultivate in vitro, so robust 3D in vivo-like culture environment are necessary for properly studying their behavior.
The chemical synthesis of our dopamine-hyaluronic acid (DAHA) composite is simple and requires a single step. The stiffness of the material is tunable by altering the degree of dopamine substitution, and was favorable for the adherence and differentiation of dNPCs, which validates its use as a tissue regrowth scaffold. Because dopamine is electrochemically polymerizable, the material is electrically active and may be polymerized directly onto electronically conducting materials. In addition, the material is stable over one hundred cyclic voltammetry cycles, which demonstrates its utility as a bioelectronics interface. More importantly, this electroactive biomaterial is composed entirely of endogenous materials from the substantia nigra (the region where dNPCs develop), and therefore represents the highest possible degree of biocompatibility for studying and interfacing with this important region of the brain.

Electronic medical implants serve as a key pillar in many therapeutic strategies. Classes of implantable devices include biosensors, controlled release systems, and tissue stimulation devices. While the sophistication of these implants has increased over recent years, there are many persistent challenges that may limit the prospective impact of permanent implantable device-based therapies. These include risk of infection, chronic inflammation, and costly surgical procedures. This talk will introduce the idea of edible electronic devices as a strategy to overcome many of these challenges. Two specific innovations will be discussed in this talk. First, the performance of edible batteries fabricated from biologically-derived melanin pigments will be examined. Second, the use of ultra-compliant electronically active hydrogels that integrate edible devices with soft tissue will be discussed. Prospective medical applications for edible electronic will be highlighted.

Electronic devices are used as implants to temporarily monitor biological activities. In most cases, an implanted electronic device requires an extraction surgery that imposes risks, cost and discomfort. In this work we present a new concept of transient materials for bioelectronics and biomedical devices. Transient materials presented in this work can be used to construct bioelectronic devises capable of monitoring and communicating biological signals. A prototype device consisting of several basic electronic components that is fully transient in bioenvironment is presented. Transient bioelectronics are capable of dissolving in their surrounding environment with no traceable remains. DMA and FTIR are used to characterize the materials for their mechanical properties and to further investigate cross-linking within the polymer composite.

Peptide nanostructures are attractive candidates for the development of novel bioelectronic devices due to their chemical diversity, which enables modifying their properties; their ease of synthesis; and their ability to self-assemble into nanometric structures. However, electrical conductivity in such nanostructures may involve the contribution of both electrons and ions, and accordingly, can critically depend on humidity. Hence, understanding how the relative humidity affects peptides' conductance is of great importance. Therefore, the main goal of this research is to study the relative humidity dependent conductance in amyloid β based peptide filaments and how it is affected by the self-assembly conditions, towards their future incorporation in electronic devices.
The peptides used in this work were based on an extension of a core sequence of the amyloid β peptide (AAKLVFF), which was modified by mutating phenylalanine with 2-thienylalanine, in order to promote electronic conduction.1 Current-voltage and impedance spectroscopy (IS) measurements revealed a bimodal exponential dependence on relative humidity. In particular, the electrical conductance is governed by ion transport at relative humidity above 60%, but has a non-negligible electron transport contribution in the lower relative humidity range. Furthermore, we demonstrate that the extent of network folding, which is controlled in this work by the self-assembly duration, affects the conductivity and the degree of dependence of ion transport on relative humidity; larger conduction was obtained for more uniform network morphology, probably due to larger amount of exposed side groups on the scaffold that could interact with water molecules to create charge carriers (OH-/H3O+).
Beyond a deeper understanding of conduction mechanisms in peptide fibril networks, this work reveals that a precise control of environmental conditions will be required for the proper operation of future peptide-based bioelectronic devices.
1 Amit, M., Cheng, G., Hamley, I.W. and Ashkenasy, N., Soft Matter 2012, 8, 8690.

Melanins represent an important class of natural pigments present in plants and animals and have been considered as a promising material for semiconducting applications. However, despite their interesting opto-electronic properties, until now there is no satisfactory understanding of some basic properties of these materials, such as the macromolecular structure, origin of intrinsic paramagnetism and absorption and luminescence features. In particular, the presence of stable paramagnetic centers evidenced by persistent ESR signals is frequently reported in the literature. These centers are sensitive to several external factors such as pH, temperature, illumination and the presence of oxidizing/reducing agents,, in such way that a wide range of distinct spectroscopic parameters have been reported. In order to better understand the origin of these paramagnetic centers, in this work we have employed electronic structure calculations to evaluate Spin Hamiltonian (SH) parameters. The ground-state geometries were fully optimized in a DFT approach with Becke&’s LYP (B3LYP) exchange-correlation functional and 6-31G basis set. The SH parameters were obtained in a DFT/B3LYP approach, employing 6-31G** and EPRII basis sets. The calculations were carried out with GAMESS (optimization) [2] and ORCA (SH parameters) [3] computer packages. The results confirm the presence of at least two groups with different values for g-factor identified in the literature as centered carbon radicals (CCRs) and semiquinone free radicals (SFRs) [4]. In particular, CCRs could be associated with anionic hydroquinone structures (HQ) and N+ hydroquinone defects (Ndef); SFRs were compatible with the semiquinone (SQ), anionic indolquinone (IQ) and anionic quinine-imine (QI) structures. These trends were confirmed in dimmers structures, suggesting a strong localization of the paramagnetic centers.
[1] P. Meredith, T. Sarna. Pigment Cell Res, Vol. 19(2006) 572-594.
[2] M. W. Schmidt et al. J. Comput. Chem. Vol. 14 (1993) 1347-1363.
[3] F. Neese. Wiley Interdiscip. Rev. Comput. Mol. Sci. Vol. 2 (2012) 73-78.
[4] A.B. Mostert, et al. J. Phys. Chem. B, 117 (2013) 4965-4972.

The Reaction Centers (RCs) of photosynthetic organisms are efficient billion-of-years optimized photoenzimes for conversion of absorbed light into charge separated states. Combination of such effective photoenzimes with π-conjugated molecules appears an intriguing strategy to obtain a new generation of versatile bio-optoelectronic materials for applications ranging from photoconversion to photocatalysis and sensing.
We present here the design and synthesis of hybrid bio-organic photosynthetic complexes by combination of the Reaction Center of the photosynthetic bacterium Rhodobacter Sphaeroides R26 with tailored molecular semiconductors. The organic molecules can act as antennas to extend the light harvesting capability of the Reaction Center, thus enhancing its photoconversion performances [1], but can be also used for charge transfer processes to external electron/hole acceptors.
We have developed protocols to synthesize tailored bio-organic complexes, exhibiting optimized interactions of the functional π-conjugated molecules with the photoenzime.
We also demonstrate that such hybrid architectures can be incorporated into the membrane of tailored polymersomes, still maintaining their full functionality, and even be anchored on electrode surfaces.
References
[1] F. Milano, R.R. Tangorra, O. Hassan Omar, R. Ragni, A. Operamolla, A. Agostiano, G.M. Farinola, M. Trotta Angew. Chem. Int. Ed. 51, 11019 (2012)

We describe an optical sensing platform, where an OLED pixel array, a sensing element, and a polymer or small-molecule organic photodetector are integrated to form a compact monitor. Sensing element design and monitoring of e.g., O2, pH, relative humidity, lactate, and glucose, including detecting multiple bioanalytes using a lab-on-CD, will be described. Monitoring dissolved O2 as a tool to study respiratory function and hence remediation of bacteria will also be described, as well as the effect of different light wavelengths and intensities on light sensitive cells in relation to cellular development and differentiation. For the latter, an array of controlled LEDs interfacing a 96 well culture plate for high content screening was fabricated. The development of a spectrometer on a chip using microcavity OLED pixels emitting in the 370 to 640 nm range will also described.

Förster Resonance Energy Transfer (FRET) is commonly used as a spectroscopic ruler for nanometer scale distance measurements. DNA photonic wires[1] are of interest for potential applications in synthetic photosynthesis, biological sensing,[2] and photonics applications.[3] Many of these applications require understanding how to engineer highly efficient energy transfer.
We have combined steady state absorption, fluorescence, ultrafast transient absorption, time-resolved photoluminescence, and single-particle (sp-)FRET measurements to examine energy transfer between Cy3 and Cy5 attached to a DNA duplex as a function of dye separation distance. The combination of these techniques allow for inhomogeneities in ensemble measurements and the contribution of direct absorption by the Cy5 acceptor molecule to be accounted for. Each cyanine dye was rigidly attached to the DNA backbone. Anisotropy measurements and increased fluorescence quantum yields confirm rigid immobile dyes. This reduces the uncertainty in dye separation as well as in the orientational factor, κ2. Energy transfer from the donor to the acceptor dye is characterized by donor emission quenching and simultaneous acceptor emission sensitization. Time-resolved and single-particle measurements are found to be more reliable for dye separations less than the Förster distance. For time-resolved measurements, we see a fast decay in donor emission and a concomitant rise in acceptor emission. We explore energy transfer over distances that are shorter than the dye molecules and thus are outside of the Förster limit. Spectral shifts in steady state absorption and acceptor fluorescence quenching indicate interaction between the donor and acceptor when in close proximity. We observe, for the smallest separation distances, picosecond energy transfer with near unity efficiency. Single distributions in efficiency are observed via spFRET measurements and transient absorption shows no signs of charge transfer. Structural models were used to clarify the distances between dyes. Deviations from Förster theory are discussed.
1 - S. Buckout-White et al., "Multimodal Characterization of a Linear DNA-Based Nanostructure" ACS Nano 6 1026 (2012)
2 - I.L. Medintz et al, "Proteolytic activity monitored by fluorescence roesonance energy transfer through quantum-dot-peptide conjugates" Nature Materials 5 581 (2006)
3 - C.M. Spillmann et al., "Achieving Effective Terminal Exciton Delivery in Quantum Dot Antenna-Sensitized Multistep DNA Photonic Wires" ACS Nano 7 7101 (2013)

In this contribution, we demonstrate the dual-detectable metal/bio-organic/n-GaN visible/ultraviolet photodetector with electrically different polarity based on DNA-CTMA biopolymer for ultra-light-sensing applications. The smart-light-sensing DNA-CTMA/n-GaN photodiode (DG-PD) shows high-performance, efficient characteristics and charge transport mechanism under dark, halogen- and UV- illuminations. The DG-PD parameters are studied using current-voltage (I-V) and transient photocurrent techniques. Measurements show that the DG-PD has low leakage current and a negative bias shift compared to reference diode without DNA-CTMA biopolymer. It is observed that the DG-PD shows excellent recognize photocurrent behavior like halogen-illumination photocurrent with 0.75 V and UV-exposed photocurrent with 1.02 V positive bias shifts compared to dark photocurrent. In addition, the zero-bias saturation current of halogen-illumination occurs at negative and UV-exposed occurs at positive bias sides. Further, a significant transient photocurrent responses observed in halogen- and UV- irradiation with electrically different polarity. These behaviors show that how the DNA-CTMA on n-GaN is quite effective for recognizing visible and UV lights as a dual-detectable photodiode. We find that the series resistance values from I-V measurements for DNA-CTMA biopolymer on different substrates. The formation and charge transport mechanisms with feasible interface energy band diagrams for DG-PDs under dark, halogen- and UV- illuminations are also discussed. These results indicate that the use of DNA-CTMA biopolymer on n-GaN is very promising for recognize of visible and UV photocurrents in smart-sensing future technologies.

In organic electronic areas, there are many challenges for chemists to develop new bio-materials and novel microfabrication techniques since the area is a part of the chemical domain, which builds up novel bio-materials at the molecular level. It allows us to develop organic bio-electronic devices/materials. In this study, we introduce a microfluidic synthesis and microfabrications of bio-sensing material, molecularly imprinted polymer (MIP), which has a highly cross-linked thermoset with receptor sites. Molecular recognition takes place by creating those receptor sites. MIP can be produced by a molecular imprinting technique, which is a general protocol for the creation of those synthetic receptor sites with specific molecular recognition functions for bio- or chemical sensors in cross-linked network polymers. Synthesis of high affinity receptor sites in MIPs systems is a key contribute to achieve high performance bio-sensors. The microfluidic approach was employed to produce high sensitivity MIP&’s particles. A novel microfabrication technique was also demonstrated to develop organic bio-electronic sensors. Those approaches resulted in novel MIP&’s system with specific advantages that can&’t be achieved by conventional techniques.

Here we report the fabrication of a ethanol sensor based on electrical readout of the sensor activity. The sensor element is based on a standard enzymatic reaction using alcohol oxidase (AOX). The transducer is a a pair of finger electrodes that will work as chemiresistors/ capacitors that detect the change caused by the hydrogen peroxide produced by the reaction between ethanol and oxygen, mediated by AOX.
The purpose of the sensor is to apply them in packages with cut-fruit to identify the degradation of the packaged fruits. The final goal is to print the sensor unit on the upper-lid of the package and sense the electrical response of the sensor via a wireless reader.
This work is carried out within the EU-funded Smart sustainable food packaging utilizing flexible printed intelligence and materials technologies (Susfoflex) project.

The integration of an organic electrochemical transistor (OECT) with human barrier tissue cells provides a novel method for assessing toxicology of compounds in vitro. Epithelial cell monolayers serve as functional barriers in the body, tightly controlling the flux of ions. Ion transport between cells is regulated by protein structures known as tight junctions. The ability to measure the function of tight junctions provides information about barrier tissue and is indicative of certain disease states. Minute variations in paracellular ionic flux induced by toxic compounds are measured in real time, with unprecedented temporal resolution and extreme sensitivity.
Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has the ability to conduct both electronic and ionic carriers, offering an unique platform for communication between biological systems and electronics. An OECT is a device in which electronic drain current within the PEDOT:PSS channel is modulated by ionic current between an electrolyte and the polymer. In the present device architecture, cell monolayers act as a barrier to the ionic current. Channel current is used to detect ion transport through the cell layer. Pursuing the work developed in our group [1], kidney MDCK cells are grown directly on the PEDOT:PSS channel of the OECT. We will present the new architecture of the OECT where the gate and the channel are in the same plan and both composed of PEDOT:PSS. Optimization of the device geometry will be presented. Optimization of the cell adhesion on the OECT will be highlighted, since it represents a key parameter to acquiring valuable data about the barrier tissue.
The planar architecture presents a number of advantages, including ease of integration with existing electronic and biosensing platforms, and compatibility with mass production roll-to-roll, and potentially low-cost fabrication schemes. Contrary to cells growth on filters, our system is compatible with established optical characterization techniques common in cell biology. Correlation between optical and electrical characteristics of epithelial cell layers will be presented.
The biosensor presented here provides a vehicle for fundamental research in the life sciences, facilitating the study of barrier tissue and factors affecting its integrity and allowing for the development of realistic in vitro cell models for drug discovery and toxicology.
1. Jimison, L.H., et al., Measurement of Barrier Tissue Integrity with an Organic Electrochemical Transistor. Advanced Materials, 2012.

Microalgae photosynthesis is an efficient conversion of sunlight into biomass. WonHyoung et al. have demonstrated that by piercing individual microalgae cells with a single nanoelectrode, the excited electrons produced by the cells&’ photosynthetic pathway can be collected[1]. According to their work, the electrons from the photosystem II pathway are shuttled to the nanoelectrodes through the redox reaction of p-benzoquinone[1]. Although this opened up an exciting possibility of using microalgae as a way of harvesting light as electric current, it was limited in its application due to their AFM-based setup; that is, it allowed only individual cells to be pierced at a time (~1.2 pA of current collected).
In our presentation, we will demonstrate, for the first time, how an array of microelectrodes can be used to harvest photosynthetic electrons from multiple microalgae at a time. The microelectrode array is prepared by a template-synthesis method[2]. This method allows us to prepare an array of protruding, gold microelectrodes, whose diameter and length can easily be tuned. From our setup, we can fabricate ~0.2 million microelectrodes that can all be used for simultaneous impalement. We will demonstrate how these arrays can be used as an array of microelectrodes, and be applied to impale model microalgae, Chlamydomonas reinhardtii cells, using simple centrifugation approach. The impaled microalgae are immobilized and electrical currents can be collected through the gold microelectrodes to external electrical circuits. We will also discuss how coating the array with a semi-conductive alumina layer prevents a buildup of a capacitive double layer. The semi-conductive alumina film is broken off from the tips of the microneedles upon impact by microalgae cells, thus creating a contact between the intracellular matrix of the cell and the gold. The details of each procedures and their efficiency will be discussed in our presentation.
References:
[1] Ryu, WonHyoung et al. “Direct Extraction of Photosynthetic Electrons form Single Algal Cells by Nanoprobing System”. Nano Letters, 10, 2010, 1137-1143.
[2] Mukaibo, Hitomi et al. “Controlling the Length of conical Pores Etched in Ion-Tracked Poly(ethylene terephthalate) Membranes”. Small, 2009, 5(21), 2474-2479.

We have developed a miniaturized prototype sensor matrix for breath analysis that can detect key biomarkers in human breath as an indicator for disease, the result and analysis of which can be transmitted and displayed on a smartphone device. This device uses engineered M13 bacteriophage (phage) as the base material. Phages are essentially programmable colloidal particles with receptor molecules on their surfaces, and they possess many desirable features that make them useful as materials for sensing applications. Fist, due to their monodispersity and high aspect ratio, phage can easily self-assemble to form various functional nanostructures to exhibit structural color. M13 phage receptor molecules can also be modified to display different functional peptides or receptors on the major (pVIII) coat proteins that can interact with various atmospheric compounds. Finally, phage building blocks are completely harmless and can be easily prepared through amplication using bacterial host cells (E. coli).
We have previously demonstrated that phage particles can be assembled into structurally colored matrices and various nanostructures, dubbed “phage litmus”. This is done through simple thin film growth process from phage suspensions, where the phage particles are organized into supramolecular structures with multiple levels of hierarchical organizations, similar to that of colloidal liquid crystals. Most notably, we can create viewing angle independent color matrices. Different colorimetric properties are also achieved through altering the number of glutamic acid (1E to 4E) at the N-terminus of the pVIII region, as well as tuning the thin film fabrication conditions.
The biosensor works by taking differential image mapping of the phage litmus, or “fingerprint” patterns, of target compounds, and matching the patterns from existing data library; the sensitivity of which can go down to the ppb regime. Preliminary results suggest that exhaled gases can interact and bind with the phage litmus, and hence a colorimetric response due to the scattering of light in the phage material, thus allowing detection of a wide range of biomarkers.

Nucleic acid detection is a common method of identifying pathogens such as viruses and bacteria. Conventionally, DNA amplification and sequencing have been used for this purpose. Unfortunately, certain pathogens only possess genetic material in the RNA phase (e.g. RNA viruses). Further, amplification-based methods tend to be time-consuming and are less suitable for rapid field-based detection. While methods are available for detecting RNA oligomers, they typically require labeling (e.g. fluorescent tags) which makes the technology more costly. For these reasons, a label-free method to rapidly identify RNA sequences, particularly in fragments, would be advantageous.
In this work, we examine the detection of RNA and DNA oligomers using surface plasmon resonance. Single-stranded DNA oligomers were immobilized on the gold sensing surface and the surface was further functionalized with poly(ethylene glycol) to minimize any non-specific binding. The binding between complementary RNA and DNA oligomers was monitored as a function of solution parameters including temperature using a sample and reference configuration to determine the melting point of DNA-RNA complexes. We have determined that surface bound DNA oligomers can be used for detection of the complementary RNA oligomers; however, both the binding capacity and melting temperature are reduced relative to complementary DNA oligomers.

Nanocomposite films of organic-capped gold nanoparticles (AuNPs) are attractive vapor sensing materials due to relatively easy preparation, simple transduction mechanism, and versatility towards different types of surface functionalization. Alkanethiol-functionalized AuNPs have been widely explored as vapor sensing elements for a variety of vapor analytes through array-based pattern recognition. However, these materials are limited by a lack of high specificity and a limited diversity available for surface functionalization. Single strand DNA (ss-DNA) oligomers are new candidates for AuNP surface functionalization with two principle merits. The first is the expansion of surface functionalization diversity by a large number of unique oligonucleotide sequences, which scales with sequence length. The second is enhanced specificity by development of aptamers for specific targets. DNA can be engineered to have complex three-dimensional structures through base-pairing and self-interactions to yield structures with molecular recognition properties. In this study, we explore these two attributes for engineering analyte selectivity. We first report vapor sensing capabilities of random DNA to show its properties as a non-specific sensor in array-based sensing, similar to alkanethiol-AuNP chemiresistive sensor arrays. Sensor responses are dependent on oligonucleotide sequences with different response patterns for each sensor/vapor combination. Next, we compare DNA sequences with specific folding properties to controls without, and demonstrate structure-dependent response characteristics for specific analytes. Through comparison for a series of organic vapors - ethanol, methanol, toluene, hexane, dimethyl methylphosphonate and 2,4-dinitrotoluene, we demonstrate that vapor specificity can be engineered by altering base sequences and three-dimensional macromolecular geometry. In addition to the selectivity advantages in these two aspects, DNA-functionalized AuNP chemiresistive sensors have sensitivity and limits of detection (LODs) comparable to state-of-the-art chemiresistors. These results support DNA-functionalized AuNP nanocomposite films as a promising material for selectivity engineering for sensor applications.

Seamless integration of biological components with electrochemical sensors is critical in the development of microdevices for cell analysis. Cell-based impedance biosensing is an emerging technology that can be used to non-invasively and instantaneously detect and analyze cell responses to chemical and biological agents. The use of bioimpedance measurements allows for the in vitro monitoring of cellular adherence, proliferation, viability, and morphological changes. The goal of this project is developing and optimizing a biosensor platform that is capable of detecting cellular changes caused by reagents down to the single cell level. The optimization of the electrode design provides the ability to monitor the changes of cell kinetics while reducing the background noise often seen in other impedance based sensors. The use of size exclusion in the design of the microelectrodes allows for the separation and detection of single cells. Mammalian Human Embryonic Kidney, which are an average of 13 microns in diameter, cells in medium were added to a microfluidic reservoir of a microelectronic device and allowed to settle to the bottom. The addition of electrodes to the bottom of the well allow for the cells to bind and cause a quantifiable change in impedance which provides real time indications of cellular changes. The ability of ECIS to give real time information about the cellular environment also presents the possibility for the detection of cellular biomarkers as a reference to test for the ability to monitor cells in-situ for the release of specific biomarkers. Rapid chip fabrication for testing is achieved through standard photolithography for creating microelectrodes on glass microscope slides. The microelectrodes provide for the cell attachment and single cell manipulation through the utilization of electric fields. Polydimethylsiloxane (PDMS) is used for the formation of the wells around the electrodes. Readings are attained using a multiplexed potentiostat to measure changes in the impedance of the cellular environment in each microfliudic well individually and simultaneously. Time lapse readings are used to monitor cell adherence over the course of the test. Impedance changes in the range of 100 ohms are observed during cell binding to the microelectrodes.

Surface functionalization and modification of conducting polymer materials has been a challenge due to the lack of chemical functionality. We have previously reported the synthesis of alkene-functionalized 3,4-propylenedioxythiophene derivatives. Here, we report the synthesis of a dialkene functionalized variant (ProDOT-diene). The chemical structure of the ProDOT-diene monomer was characterized by Nuclear Magnetic Resonance (NMR). The resulting polymer was electrochemically polymerized and characterized with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). With the alkene side groups, highly efficient post-polymerization functionalization of the conducting film was successfully achieved via a radical-based thiol-ene “click” reaction with various terminal thiols under mild conditions. Examples of side group chemistries that have been so far examined include branched alkanes, ethyloxys, and ferrocenes. The modified polymer films were examined by a variety of analytical techniques including CV, scanning electron microscopy (SEM), and Fourier Transform Infrared spectroscopy (FTIR). This method allows for efficient, facile tuning of the surface chemistry of poly (3,4 -propylenedioxythiophene) (PProDOT) films, thus making it possible to tailor the physical and biological properties such as conductivity, wetting ability and biocompatibility of these films for different applications.

Protein sensing is an issue with great interest in medical and biological applications. One possible approach to protein detection takes advantage of measuring changes in fluorescence resonance energy transfer (FRET) between a fluorescent donor and an acceptor within a protein which undergoes induced changes in conformation. This technique has grown in popularity due to the emergence of various fluorescent proteins with shifted spectral properties. To accomplish this process it is necessary thee detection of low intensity fluorescent signals in the visible spectrum.
In this paper we analyzed the emission spectrum obtained from fluorescent labels attached to a protein which changes its conformation in the presence of glucose using a commercial spectrofluorometer. Different glucose nanosensors were used to measure the output spectra with fluorescent signals located at visible bands of the spectrum.
A new device is presented based on multilayered a-SiC:H heterostructures to detect identical transient visible signals. The transducer consists of a p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructure optimized for the detection of the fluorescence resonance energy transfer between fluorophores with excitation in the violet (400 nm) and emissions in the visible range of the spectrum. The device was characterized through transmittance and spectral response measurements (400-800 nm), under reverse electrical bias (-10VResults show that the device photocurrent signal measured under reverse bias and using appropriate steady state optical bias, allows the separate detection of the fluorescence signals.
An electrical model, supported by a numerical simulation, gives insight into the transduction mechanism.

Significant advances have been made in the last two decades in interfacing electronic devices with biology. Bidirectional interaction with living tissue is broadly investigated today, and multiple options in sensing and stimulating physiological activity are now available. Organic devices such as the organic electrochemical transistor (OECT) and the organic electronic ion pump (OEIP) have shown promise, but their integration at high resolution in an implantable probe is still challenging.
The use of organic materials as passive and active components exhibit mechanical and physical properties, which better match with biological environment such as the brain, and thus reduce the invasiveness of such devices compared to standard materials such as silicon.
While polymeric materials present a promising route for biological interfacing, the patterning process of such materials is challenging. Indeed, it requires the availability of patterning techniques that are compatible with chemically sensitive materials; such that standard silicon-based processes cannot be used.
This work presents the use of orthogonal photolithography to pattern flexible implantable probes devices dedicated to chronic neural interfacing. We developed a platform that allows the implantation of probes embedding multimodal organic devices at high resolution. The flexility of the device also allows making chronic recording and accessing different parts of the brain such as frontal lobe.

The scope of wearable technology stretches beyond electronic gadgets, and has the potential to revolutionize both in-hospital and in-home health monitoring. However, wide implementations of wearable medical sensors is hindered largely due to non-conformality of conventional printed circuit boards (PCBs) and solid-state electronic components. Leveraging the recent advances in flexible electronics, an integrated sensor platform has been established, which employs solid-state electronic components and utilizes conformality of flexible electronics.
In this work, we demonstrate a flexible and wearable sensor board composed of a printed electrode array capable of measuring biopotential and bioimpedance. While using a thin (35µm) PEN substrate improved conformality of the sensor board, flexure cuts further improved skin-electrode contact. Inkjet printed gold nanoparticles were used for electrodes and routing due to chemical inertness and biocompatibility of gold. Minimum feature size of 70µm was routinely achieved with sheet resistance of 0.5 Omega;/sq at annealing temperature of 200° C. The sensor board was interfaced with a polyimide flex board that hosted solid-state electronic components for data processing and transmission. The flexible sensor board provided significant edge over conventional rigid PCBs by providing high resolution data from conformal surfaces. Overall, we demonstrate a wearable flexible sensor platform that can efficiently extract biomedical signals from conformal surfaces without compromising signal quality and can transmit data over “state of the art” wireless links.

Owing to the high performance, low-cost, flexibility and simple fabrication processes, organic thin film transistors (OTFTs)-based devices have emerged as a viable platform for the biological and chemical sensing applications. Organic electrochemical transistors (OECTs), an important type of OTFTs, have shown huge potentials for state-of-the-art sensor platforms in various sensing applications.
OECTs based on Poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT: PSS) with gate electrodes co-modified with bio-molecules, biocompatible polymers and graphene-based materials have been successfully used for the following three types of sensors by us recently. (1) Glucose sensors. The OECTs with GOx-CHIT-Graphene/Pt modified gate electrodes show linear responses to glucose in a broad concentration region from 10 nM to 1 µM and interfering effect caused by uric acid and L-ascorbic acid is almost negligible for practical applications. (2) Dopamine sensors. The device with Nafion(1.0%)-Graphene /Pt modified electrode can detect dopamine down to 5nM, which is much lower than that of conventional electrochemical approaches employing the similar functionalized electrode. The interference induced by uric acid (UA) or ascorbic acid is effectively eliminated by the modification of Nafion on the gate electrode. (3) Uric acid sensors. Adopting the multilayer modification techniques, OECTs have also been successfully used as the high performance UA sensor. The sensor with UOx-GO /PANI/solution-based graphene/Pt modified gate electrode can detect UA down to 10 nM, which is approximately 4 orders of magnitude lower than that of the conventional electrochemical UA sensor. A good linearity region from 100 nM to 500 mu;M was obtained and error signals from some common bio-active interferents are largely reduced.
In summary, OECTs with functionalized gate electrodes are promising for high performance biosensors. It is expected that OECTs can be further explored for many other types of biosensors based on same principle.

Development of modern electrochemical biosensing devices requires new sophisticated systems for surface modification. Attachment of macromolecules on electrodes results in various modified surfaces with properties suitable for biosensing applications. A very promising class of polymers for such surface modifications is the group of so called switchable polymers. These macromolecular compounds undergo sharp reversible phase transitions in response to external stimuli such as temperature or pH and enable so a simple way for rapid variations of surface properties.
Different methods have already been used in investigating switching phenomena of thermoresponsive polymers on gold surfaces. The choice of a suitable technique depends on the property of interest which changes during the phase transition process to be observed. In this study, it is shown how the pH dependent structural reorganization process in the temperature responsive polymer film can be monitored by electrochemical means. [1]
For this purpose the thermoresponsive polymer from the class of poly(oligoethylene glycol)-methacrylate polymers (poly(OEGMA)) with carboxy functions containing side chains was synthesized and properly characterized in aqueous solutions. The behavior of the polymer covalently grafted to gold substrates is investigated using cyclic voltammetry (CV) in ferro-/ferricyanide solutions. Peak currents and peak separation have been found as indicators for structural changes on the surface. The experiments indicate modified access for the redox couple after the change in polymer conformation. The temperature at which structural changes on the electrode surface can be detected declines with increasing pH. This is different to the situation of the polymer in solution, suggesting different mechanisms in both cases. Finally biorecognition reaction between a short FLAG peptide (N-Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys-C) covalently immobilized on the polymer interface and the corresponding IgG antibody was performed. The effect of the bioconjugation on the responsiveness of the electrode system is described, giving inspiration for the potential development of a biosensor device based on smart macromolecular compounds.
[1]: ChemPhysChem 2012, 13, 2020 - 2023

Tactile sensing/imaging has been an important area of research for its applications in artificial skin, flexible electronics, human-electronics interfacing, and micro-electromechanical system (MEMS). Major research efforts have been focused on improving the sensitivity, spatial resolution, response time, long-time stability, and cyclic reliability of the pressure sensor devices and the integrated matrix. But one common limitation is that most of these sensors rely on an externally supplied power source, otherwise none of them will work. To solve this problem, the nanogenerator based sensor was introduced by converting the mechanical inputs into electrical output signals without applying an external power source, which is referred as a self-powered active sensor. Most recently, the triboelectric nanogenerator (TENG) has been invented as a promising energy conversion approach for sustainably and continuously driving personal electronics. So far, limited work has been demonstrated of using TENG as a self-powered pressure sensor, especially in a quantitative way.
Here, we demonstrated a flexible triboelectric active sensor (TEAS) with excellent performance and low processing cost. The working principle of the TEAS is similar to the TENGs and was theoretically verified by numerical calculations with finite element method (FEM). Both static and dynamic pressure sensing were accomplished by the same device with different measurement approaches. Specifically, the open-circuit voltage as well as the amount of the transferred charge density was employed for static pressure detection, while the pulse-like short-circuit current peak was used for dynamic pressure monitoring. Owing to this active sensing principle, a supreme performance of pressure detection was achieved on the TEAS, including high sensitivity of 0.31 kPa-1, fast response/relaxation time of < 5 ms, long-term stability/reliability of 30,000 cycles, as well as a low detection limit of 2.1 Pa. Multiple TEAS devices were integrated into a sensor array for tactile imaging, and distinguishable spatial profiles of the sensor array were realized for self-powered monitoring and mapping the applied local pressures distributions. This work is an unprecedented progress towards the practical application of nanogenerators, the realization of self-powered system, and further advancement of flexible electronic devices. [1]
[1] Lin, L.; Xie, Y. N.; Wang, S. H.; Wu, W. Z.; Niu, S. M.; Wen, X. N.; Wang, Z. L. ACS Nano 2013, 7, 8266-8274.

A novel dual-amplification immunosensing strategy by integrating of macroinitiator and surface-initiated polymerization was proposed. Because of excellent water solubility, functional groups for covalent binding of initiators and/or other biomolecules, and minimal nonspecific interactions with test surfaces, a copolymer poly(acrylic acid-co-acrylamide) [P(AA-AM)] was deservedly employed as a macroinitiator carrier in this work, in order to bring multiple polymerization reaction centers (i.e. initiators) to each sandwish immune event for subsequent polymerization-based signal amplification in protein detection. The carboxyl groups and a fraction of amino groups of the high molecular weight copolymer P(AA-AM) were applied to couple with streptravidin and water-soluble ATRP initiators, respectively. After immunoreaction, the biotin-labeled antibody on the surface of substrate was reacted with macroinitiator through streptravidin-biotion specific identification, and then the purge-free activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP) of 2-hydroxyethyl methacrylate (HEMA) was triggered, which was expected to improve the detection sensitivity significantly. As a result, scanning electron microscopy (SEM) measurement showed clear signal amplification via using macroinitiator compared with small single molecule initiator.
The dual-functional macroinitiator could be endowed with the abilities of triggering polymerization and biomolecule recognition. It was known that the long polymer chains that derived from polymerization contained abundant repeating units, and as a result a single biological molecule identification process kept in one small monomer would be amplified hundreds of millions of times through the chain extending. On the other hand, the total amount of grafted polymeric materials could also be increased by producing more polymer chains per binding event in advance . So the increased amount of initiators formed on the basis of polymer segment of poly(acrylamide) in P(AA-AM) could further improve the polymerization and enhance the signal output.
The growing polymer chain provided numerous hydroxyl groups, which led to the change of the hydrophily of substrate surface in favor of the contact angle measurement within 7 min. Additionally, the polymer formed on the surface of substrate also altered the surface reflectivity and opacity, which also led to directly visible to the naked eye within 10 min by virtue of signal amplification. The presented method was successfully demonstrated to be easy to perform and less time-consuming, and showed great potential to detect other proteins in practical samples only with simple modification of procedure.

The focus of this work is on the numerical investigation of the charge transport properties of the de novo-designed alpha3-peptide, as well as its variants 5Q-alpha3 and 7Q-alpha3. Their charge transport properties are investigated within a tight-binding model Hamiltonian, using Dyson's equation together with a transfer-matrix treatment to solve a time independent quantum Schrödinger equation. The input parameters (amino acid vertical ionization and dipeptide hopping energy) were obtained by performing ab initio calculations within the Density Functional Theory (DFT).
The alpha3-peptide is a 21-residue peptide with three repeats of the seven-residue (heptad) sequence Leu-Glu-Thr-Leu-Ala-Lys-Ala, which forms an alpha-helical bundle structure through hydrophobic interaction between Leu residues. The 5Q-alpha3 and 7Q-alpha3 peptide is obtained by Ala → Gln substitution at the 5th and 7th position, respectively, of the alpha3-peptide amino acid sequence. The alpha3-peptide and its 5Q-alpha3 variant has the ability to form fibrous assemblies that are observed by transmission electron microscopy and atomic force microscopy, whereas the 7Q-alpha3 does not.
Our main aim is to investigate whether or not the biased alpha3 polypeptide and its variants can be also identified by quantum charge transport measurements through current-voltage (IxV) curves as a pattern to characterize their fibrous assemblies. From their IxV profiles, we found that the alpha3 peptide, which presents the most fibrous assemblies, shows the smaller current saturation, whereas the 5Q-alpha3 variant, which forms fibrous assemblies more attenuated than those of the alpha3 peptide, has a current saturation higher than alpha3, but smaller than 7Q-alpha3. Finally, the 7Q-alpha3 variant does not form fibrils and shows the highest current saturation, suggesting that charge transport in peptides can turn to be a useful tool for the development of biosensors to probe the onset of amyloidosis-like diseases. If the secondary structure of the peptides is considered, the number of charge transport channels should increase due to hydrogen bonding related to the secondary structure, further increasing saturation currents, but not specifically enough to change the order I(alpha3) < I(5Q-alpha3) < I(7Q-alpha3). We hope that this biomedical application
of the charge transport in proteins and polypeptides should stimulate experimental and engineering technological developments.
Acknowledgments: This work received financial support from the Brazilian Research Agencies CAPES (Rede NanoBioTec), CNPq (INCT-Nano(Bio)Simes and Casadinho) and FAPERN/CNPq (Pronex).
References
[1] S. Kojima et al, Biochim. Biophys. Acta. 1294, 129 (1996).
[2] L.M. Bezerril et al, Appl. Phys. Lett. 98, 053702 (2011).

We develop a new method for sensing sweat electrolytes [Na+] and [K+] levels with Optical Measurements. We have incorporated the use of Lawsone (2-hydroxy-1,4-naphthoquinone) where [Na+] and [K+] ions can bind to so the different concentrations of electrolytes would cause different absorption intensities. We have studied the effects of [Na+] and [K+] doped Lawsone thin films recently and showed that doping in Lawsone with electrolytes results in absorption at a particular wavelength region that is 400 nm - 500 nm. There were two parts of sweat collection Dehydration and hydration. In the first part, the subjects were Fasting for 12 hours. We use a disposable plastic wrap that fit to the subject forearm the area of (550 cm2) at room temperature and humidity (25 C and 55% respectively). We analyzed the sweat with flame photometry and compared the results with Ultraviolet-visible (UV-Vis) measurements of Lawsone that is dissolved in sweat. Our results showed that there is a correlation between absorption peak at 400 nm - 500 nm region and the concentration of the electrolytes in sweat. This important finding could be used to develop a microscale optical sweat sensing device as a point-of-care solution for athletes and soldiers where physical and cognitive performance would play a crucial role.

Nowadays there are a lot of interest to investigate the DNA&’s potential applications in nanoelectronic devices, not only as a template for assembling nanocircuits, but also as an element of such circuits, triggering a series of experimental and theoretical investigations. Besides, using a full range of quantum mechanical and biochemical methods, studies on the conformational behavior of DNA-based molecules with periodic/quasiperiodic nucleotide sequences have now established that they are a promising biological medium for the efficient transport of charge carriers.
Many interesting theoretical results concerning the electronic properties of one dimensional chains have been obtained by using the Schrödinger equation in the tight-binding approximation. A considerable amount of work has been devoted to the study of this equation, for both random and quasiperiodic sequences of the on-site potential and/or the hopping potential between the quantum states.
Recently [1], it was shown that the knowledge of thermal properties, like the specific heat and chemical potential, may be useful to characterize different genetic diseases, such as the neurodegenerative ones (Alzheimer and Parkinson, among them). As the characterization of biomolecules presents a high degree of complexity together with a high level of precision, approximate methods must be used.
It is the aim of this work to push this field forward by investigating the thermal properties (the electronic specific heat spectra) of quasiperiodic extended ladder model mimicking a double-strand DNA (ds-DNA) segments, considered as a sequence of four possible nucleotides, namely guanine G, adenine A, cytosine C and thymine T, arranged according to the Fibonacci and Rudin-Shapiro quasiperiodic sequences. For comparison we consider a segment of the first sequenced human chromosome 22 (Ch22), whose arrangement was retrieved from the internet page of the National Center of Biotechnology Information. We utilize here the same theoretical model used in Refs. [2,3], which is based on a tight-binding model and fits well all experimental data. Our main aim is to investigate the role of aperiodic order in different electronic specific heat (ESH) spectra profiles, seeking possible differences and similarities among them, with the purpose to establish some kind of standard behavior.
Acknowledgments: This work received financial support from the Brazilian Research Agencies CAPES (Rede NanoBioTec), CNPq (INCT-Nano(Bio)Simes and Casadinho) and FAPERN/CNPq (Pronex).
References
[1] G.A. Mendes et al, Chem.Phys.Lett. 542, 123(2012).
[2] R.G. Sarmento et al, Phys. Lett. A 376, 2413 (2012).
[3] M. Zilly et al, Phys. Rev. B 82, 125125 (2010).

We have developed a novel vertical nanogap device (VND) structure with bare semiconductor contacts as electrodes, to investigate electronic transport phenomena in bio-electronic systems. The device fabrication starts from a Silicon-on-Insulator (SOI) substrate comprising a buried SiO2 (BOX) layer of few nm thickness, embedded within two degenerately p+-doped (boron, 0.001 - 0.005 Omega;cm), single crystalline silicon layers. Individual devices were fabricated by standard photolithography and a combination of anisotropic (tetramethylammonium hydroxide, TMAH) and selective (hydrofluoric acid, HF) wet etching techniques, resulting in well-conductive silicon contacts separated by a nanogap of either 8 ± 1 nm or 4 ± 1 nm, depending on the chosen BOX thickness. For initial verification of the device electrical functionality, gold nanoparticles (diameter 15 nm) were successfully trapped onto the nanogap electrodes using AC dielectrophoresis. Subsequently, we have functionalized our silicon nanogap electrodes with Cytochrome c. This protein, which is found in many organisms as part of the electron transport chain, has already been demonstrated to sustain electronic transport even when embedded in macroscopic, dry solid-state device architectures [1]. Current-voltage measurements were performed on VNDs after protein deposition from solution, revealing a significant increase in junction conductance of typically up to 5 orders of magnitude at 2 V. Our temperature-dependent current-voltage characteristics measured from 20 K to 340 K indicated activated transport though Cytochrome c with activation energies in the range 50 -100 meV.
[1] N. Amdursky, I. Pecht, M. Sheves, and D. Cahen, “Electron transport via cytochrome c on Si-H surfaces: roles of Fe and heme.,” J. Am. Chem. Soc., vol. 135, no. 16, pp. 6300-6, Apr. 2013.

In living systems, protonic and ionic currents are the basis for all information processing. As such, artificial devices based on protonic and ionic currents offer an exciting opportunity for bionanoelectronics. Proton transport in nature is important for ATP oxidative phosphorylation, the HCVN1 voltage gated proton channel, light activated proton pumping in bacteriorhodopsin, and the proton conducting single water file of the antibiotic gramicidin. In these systems, protons move along hydrogen bond networks formed by water and the hydrated biomolecules (proton wires). Along these wires, protons hop according to the Grotthuss mechanism. We have previously demonstrated complementary H+- and OH-- FETs with acid and base doped biopolymer proton wires and PdHx proton conducting contacts. Here, I will discuss a new class of proton-conducting devices based oh highly conductive proton wires that emulate brain synapses and display memristive behaviour.

Accurate intracellular recording of action potentials is important to understand the physiology of electrically-excitable cells such as neurons and cardiomyocytes. These recordings provide valuable information on the behaviors of different ion channels as well as the properties of the plasma membrane. Traditional intracellular recording method such as whole-cell patch clamp requires rupturing a portion of the plasma membrane to access the cell interior directly. On the other hand, extracellular recording methods such as multi-electrode arrays afford noninvasive and multiplexed measurements but sacrifice signal strength and quality. Recently, we and others developed nanoelectrodes combine the strength of both techniques and offer long term, minimally invasive and multiplexed intracellular recording (Nat. Nanotechnology 7, 185-190 (2012)). Here we present the application of our vertical nanopillar electrodes to measure action potentials in human stem cell derived cardiomyocytes. Our method not only reliably distinguishes different cardiac cell types (ventricular, atrial, and pacemaker) but also monitors their electrophysiological changes for more than a week. A comprehensive circuit simulation matches our experimental recording.

Dry bacteriorhodopsin, bR, (with only tightly bound H2O, needed to maintain the natural conformation, retained) is a fascinating candidate component for biomolecular electronics, considering the combination of its mechanical stability, electrical conduction and versatile optical and chemical properties. This promise and the conflicting results that have been reported, led to the present study. Electron transport across dry bR monolayers is governed by thermally activated hopping > 160K, along with tunneling via super-exchange at lower temperatures. Transport is dominated by the retinal cofactor, and protein conformation. As bR is a trans-membrane protein, in nature it is surrounded by membrane lipids from all but its top and bottom sides. For possible practical use as high a concentration of the active membrane component as possible is needed and to that end we studied monomeric lipid-deleted bR (dLbR). Monolayers of dLbR on conducting substrates are stable and maintain the photoactivity of the native membrane-bound protein. Electron transport across dLbR monolayers, both in dark- and light-adapted intermediate states, can only be probed under optical illumination at controlled humidity conditions. Such measurements were performed by conducting-probe AFM on junctions that contain only a few monomers. Such measurements need to be done at tip forces <10 nN, the limit of elastic behavior (i.e., at higher forces irreversible changes occur). We find green light-induced current enhancement and conductance modulation upon subsequent blue illumination in this configuration. The effect associated with bound water molecules on electronic transport was found by changing the external relative humidity (to affect the number of water molecules inside the protein) and probing junction conductance. Remarkably, we find significantly increased electronic conductance at higher humidities, suggesting that conformational effects are involved. Apart from their scientific value, these results emphasize the building block potential and relevance of dLbR for future bioelectronics.

Due to their technological relevance, proton conductors constitute an important class of materials for further research and development. We have recently discovered bulk proton conductivity in thin films from a cephalopod structural protein. In the solid state, this protein features high conductivities and excellent general electrical figures of merit, which compare favorably to those found for artificial materials. The unique physical and electrical properties of our protein facilitate the demonstration of the first protein-based protonic transistors. In their totality, our findings represent an important step towards the next generation of fully biological proton conducting materials.

Membrane proteins perform many important functions in living cells, which makes them potentially important components of the bioelectronic toolkit. Integrating membrane proteins with nanoelectronics requires a versatile biocompatible matrix that can preserve the protein functionality. We accomplish this task by using hierarchical assembly of lipid molecules and membrane proteins onto a nanowire transistor to create a 1-D bilayer device—a nano-bioelectronic device that can convert proton and ion transport events into electrical signals. This presentation will discuss several examples of these devices that use passive ion channels and active ATP and light-driven pumps. Another distinctive feature of biological systems is their widespread use of chemical modifiers and co-factors to alter the signal transduction characteristics. I will present several examples that realize a similar concept in bioelectronic devices by using additional biological components to regulate the device performance. This research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences.

Charge transport (CT) through DNA has been extensively studied, and yet the mechanism of this process is still not yet fully understood. Besides the benefits of understanding charge transport through this fundamental molecule, further understanding of this process will elucidate the biological implications of DNA CT and advance sensing technology. Therefore, we have investigated the temperature and length dependence of DNA CT by measuring the electrochemical response of DNA monolayers modified with a redox-active probe. By using multiplexed electrodes, we are able to compare square wave voltammetry of distinct DNA sequences under identical experimental conditions. We vary the position of the probe, within a well matched DNA duplex, in order to investigate distance dependent kinetics. Using a model put forth by O'Dea and Osteryoung and applying a nonlinear least squares analysis we are able to determine the charge transfer rates (k), transfer coefficients (α), and the redox active surface concentration (Γ*) of the DNA monolayer. The yield of transport is strongly connected to the stability of the duplex, linearly correlated to the melting temperature of the duplex. Additionally, the results show Arrhenius like behavior for multiple probe locations, with the transport rates following a 1/L length dependence, consistent with a hopping mechanism of transport. These results begin to clarify the significance of length and sequence on the stability of the duplex, which in turn, may be used to establish the guidelines for using DNA as a molecular wire in nanoscale electronics and sensing applications.

Methylation of Cytosine bases in DNA is known to play a crucial role in many biological processes, such as the regulation of gene expression, X chromosome inactivation. They are also responsible for diseases including cancer. Targeting and identifying methylated DNA is therefore important for disease diagnosis and drug design. Current detection techniques involve chemical modification, which may not be trustworthy in distinguishing small changes during the amplification processes. Recently, new techniques using the electrical properties of DNA bases have been used to detect methylated bases [1, 2]. The results show that the methylated sequence/base can be identified with conductance measurement. In this work, we study charge transport through the 8 base-pair methylated DNA strand and its native counterpart used in the experimental work of reference [2]. Our approach consists of two steps [3]: (1) using ab initio calculations to obtain the Hamiltonian and overlap matrices of DNA strands and (2) using the Landauer-Buttiker method and Green&’s function approach to compute the transmission and linear response conductance of the strands. To fully mimic the solvated experimental condition, we employ the polarizable continuum model (PCM) in Gaussian 09. We first look at the highest occupied molecular orbital (HOMO) distribution of the two strands. We find that for the native strand, the charge density tend to accumulate more on the Guanine bases and the charge on Cytosine bases is smaller than that of methylated strand. We further analyze the HOMO parameters for the two DNA molecules, including the on-site energy for each base and hopping integrals between neighboring bases both within and between the two complementary strands. We find that the most significant differences lie in the on-site energies of Cytosine bases and the intra-strand hopping integrals between two nearest Guanine and Cytosine bases. The on-site energies of the methylated Cytosine bases are approximately 200 meV lower than that of native Cytosine bases. The intra-strand hopping integrals between two nearest Guanine and Cytosine bases for a methylated strand are about 40 meV larger than that of native strand. The HOMO analysis indicates the small modification on Cytosine bases can cause a change in the electronic properties of strand and therefore transport properties. Our calculations show that the conductance of the methylated DNA strand is smaller than that of the native one, which is in qualitative agreement with the experimental results in [2]. We then calculate the ionization potential (IP) for native strand and its methylated counterpart. We find that the IP for methylated strand is around 20 meV higher than that of native one, which lends further support to our conclusion.
[1] M. Tsutsui, et al., J. Am. Chem. Soc., vol. 133, pp. 9124 (2011)
[2] J. Hihath, et al., J. Phys.: Condens. Matter, vol. 24, pp. 164204 (2012)
[3] J. Qi, et al., Phys. Rev. B, vol. 87, pp. 085404 (2013)

Shewanella oneidensis MR-1 is a well-characterized dissimilatory metal-reducing bacterium that has burgeoned as a model exoelectrogenic species in the last decade. Appropriately poised graphite electrodes may serve as electrochemical electron accepting proxies for MR-1's native respiratory substrates (such as ferric iron minerals), and this has allowed for excellent electrochemical characterization of the species in 3-electrode type reactors. In particular, many studies have explored the mechanistic roles and interplay of the Mtr (metal reduction) electron transport pathway and the biosynthesized flavin electron shuttles that are characteristic to MR-1. From these studies, it is now well understood that MR-1 respires (i.e. donates electrons) in anaerobic environments by utilizing a combination of both direct electron transfer (DET) through cytochromes of the Mtr pathway and mediated electron transfer (MET) via redox cycling of flavin molecules between the bacterium and the acceptor surface.
Recently, a growing body of literature has suggested that chemical modification of various microorganisms with micromolar concentrations of membrane-intercalating conjugated oligoelectrolytes (COEs) will accelerate extracellular electron transport (EET) from the organisms to an electrode acceptor. The universal observation of such EET acceleration would seem to be analogous to the natural EET observed in MR-1, but up to this point, a straightforward mechanistic picture of the accelerated EET afforded by COEs has remained elusive. From a technology-development standpoint, it is extremely important to understand this acceleration mechanism and whether DET or MET processes are involved. MR-1 undergoes both types of EET and thus serves as an excellent model organism for exploring exactly this COE-EET mechanism. This presentation will outline the 3-electrode amperometry and voltammetry, as well as electron microscopy and other experiments, which suggest that COEs increase anodic respiration of MR-1 via DET by activating a subdued electrochemical pathway (non-flavin, non-cytochrome, but still biological) without significant cytotoxicity. These results may have strong implications for understanding the effect of COEs on other species in bioelectrochemical systems.

The ubiquitous biomolecule eumelanin is widely studied for its photoprotective, thermoregulating, free-radical scavenging, and anti-oxidant functions in the human body. Recently, eumelanin received increased attention for potential applications in organic bioelectronics due to its unique set of physicochemical properties including strong broad-band UV-Vis absorption, metal chelation properties, and potentially mixed electronic-ionic conduction [1,2]. This interest has been spurred by recent progress in eumelanin thin film processing. Although the amorphous semiconductor-like properties of eumelanin were already discovered in the 1960s-70s [3], the mechanism of charge transport remains one of the unresolved enigma about this black, chemically and structurally heterogeneous pigment, whose properties strongly depend on the hydration state.
We present results from the charge transport characterization of eumelanin films in controlled hydration conditions, in planar two-electrode configuration using Pt and PdHx electrodes.
Hydration-dependent current/time characteristics, Kelvin probe force microscopy, and electrochemical impedance spectroscopy measurements were conducted with electrodes more stable than Au electrodes previously considered [4] and shed new light onto the charge carrier dynamics in eumelanin thin films. Particular attention was paid to monitoring the electrochemical activity of the films, even at low electrical biases (0.2-0.5 V).
Electrolyte gated melanin devices were also fabricated using as the gating medium aprotic, hydrophobic ionic liquids, with the aim to shed light on the electronic component of charge carrier transport in eumelanin thin films.
Our results on eumelanin thin films are a further indication of the important role of ions/protons in eumelanin charge transport, as has been recently suggested based on spectroscopic measurements on eumelanin pellets [2].
[1] M. D&’Ischia et al., Angew. Chem. Int. Edit. 48, 3914 (2009). [2] A. B. Mostert et al., Proc. Natl. Acad. Sci. 109, 8943 (2012). [3] J. McGinness et al., Science 183, 853 (1974). [4] J. Wünsche et al., Adv. Funct. Mater., accepted (2013).

The high operative voltages, the low mobility of semiconductors and their poor stability in oxygen-rich and/or liquid environments are probably the most relevant problems that are significantly limiting the employment of organic thin film devices in applications for sensing in liquid and in particular, with living cells.
By combining an ultra-thin dielectric layer with a self-aligned architecture, Organic Thin-Film Transistors (OTFTs) with ultra-low operational voltages (<2 V) and a very high (100 kHz) cut frequency have been obtained. A dramatic reduction of the parasitic capacitances leading to a remarkable increase of the cut-off frequency, has allowed obtaining devices that properly work with signals at frequencies as high as those of the electrical activity of excitable cells. In addition, these optimized structures may be successfully employed also for sensing other chemical parameters in liquid solutions as for instance, pH. In this way, information about both electrical and metabolic activity of living cells can be obtained with the same kind of devices. The realization of low cost, plastic, smart substrates for cell culture is a realistic perspective for these devices.

Cellular lines models are widely used to study cell behavior under different conditions. Epithelial cells are the most analyzed in vitro system, especially when they are grown as monolayers over a solid surface in two dimensional cultures. In these conditions, the cells keep many of the original characteristics; however recent reports show that the use of solid matrix to growth cells, or three dimensional (3D) cultures, mimics tissue characteristics, so the response to a specific stimulus is different than in monolayer, and more in vivo like. One of the protein complexes dedicated to sense these changes is the tight junction (TJ), which is localized in the most apical region of the epithelial cells. The main technique to analyze the barrier function of tight junction is the measurement of the transepithelial electrical resistance, which determines the ion flux through TJ; previously in our group an Organic Electrochemical Transistor (OECTs) was developed to accurately record the TJ barrier activity. In the present work we combine the 3D culture and the OECTs to analyze the tight junction in a 3D system such as kidney epithelial cyst. We determined the optimum conditions of the cyst culture in a Matrigel matrix, the biochemical characterization, as well as the barrier properties of the tight junctions under different stimuli.

We present the integration of an organic electrochemical transistor (OECT) with an epithelial cell monolayer to create a cell based sensor for barrier tissue integrity. Epithelial cell monolayers serve as functional barriers in the body, tightly controlling the flux of ions. Ion transport between cells is regulated by protein structures known as tight junctions. The ability to measure the function of tight junctions provides information about barrier tissue and is indicative of certain disease states. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has the ability to conduct both electronic and ionic carriers, offering a unique platform for communication between biological systems and electronics. In an OECT, the electronic drain current within the PEDOT:PSS channel is modulated by ionic current between an electrolyte and the polymer. In the present device architecture, cell monolayers act as a barrier to the ionic current. Channel current is used to detect ion transport through the cell layer.
Kidney MDCK cells are grown directly on the PEDOT:PSS film of the OECT. The transparency of the PEDOT:PSS allow optical observation of the cells. The recording of the barrier resistance - measured by the OECT - was performed simultaneously with taking optical images of this barrier. The introduction of pathogenic agents, such as Salmonella Typhimurium, to a healthy cell monolayer results in degradation of tight junction proteins and can be monitored both electrically and optically throughout the time-course of infection. Adding fluorescent markers to the pathogen agents allows a better understanding of the infection effect to the barrier tissue integrity.
The biosensor presented here provides a vehicle for fundamental research in the life sciences, facilitating the study of barrier tissue and factors affecting its integrity and allows for the development of realistic in vitro cell models.

In cell biology, active control over the parameters related to cultivation such as adhesion, proliferation and detachment of cells is desired. Today, detachment typically involves enzymatic treatments that unfortunately damage surface proteins of the cells. In areas such as tissue engineering there is therefore a need for alternative, less harmful methods. In addition, spatial control is of great interest to enable selective cell detachment.
Using a self-doped and water-soluble derivative of the conducting polymer 3,4(-ethylenedioxythiophene), PEDOT-S:H, we have enabled electronic control of cell detachment at physiological conditions. When the polymer is electrochemically oxidized it swells, cracks and finally disrupts and detaches from the underlying substrate. Any cells cultured on top of the polymer will detach along with it. The detachment mechanism of PEDOT-S:H involves strain induced by an increased degree of self-doping for charge compensation upon oxidation as well as swelling due to inflow of electrolyte. When increasing the magnitude of the applied potential, detachment is faster, enabling fine-tuning of the detachment time.
Detached cells can be collected for analysis or further cultivation. When detaching human epithelial cells we found that the surface antigens were preserved to a much greater extent as compared to using enzymatic treatment methods. In addition, detached cells could be re-seeded and assumed a normal morphology, indicating that the detachment process caused no damage.
We have also patterned PEDOT-S:H using standard photolithography to realize matrix structures, opening up the possibility for selective detachment of individual parts of a polymer film. This has been used to selectively detach different types of human skin cells from a mixed cell culture on top of a PEDOT-S:H matrix.

Organic Electrochemical Transistors (OECTs) are emerging as devices ideally suitable for biological sensing and bio-electronics[1]. We here show OECTs operating in bio-liquid environments sensing and monitoring biomolecules at high sensitivity. The devices, based on the conductive polymer PEDOT:PSS, operating at low-voltages in liquids, confirm to be an ideal interface between electronics and biology.
In particular we will discuss our recent achievements in biosensing relevant for nanomedicine and drug delivery applications: detection and monitoring of drug-loaded liposomes and liposome-based nanoparticles [2] real time studies and analysis of redox properties of phase-responsive pigment biopolymers[3]. Finally we achieved the ability to directly study drug stress and death on cells cultivated on a Transwell membrane, directly integrated in the OECT. We will show the first observation of cellular death, induced by drugs and other chemical substances on normal and cancer cells, achieved by monitored the device output current that is sensitive to the cells death. These studies pave the way to OECTs as low cost and disposable devices for the monitoring drugs action dynamics.
[1] G. Tarabella, F. Mahvash Mohammadi, N. Coppedè, F. Barbero, S. Iannotta, C. Santato and F. Cicoira, “New opportunities for organic electronics and bioelectronics: ions in action”, Chemical Science, 2013, 4, 1395-1409.
[2] G. Tarabella et al., “Liposomes Sensing and Monitoring by Organic Electrochemical Transistors Integrated in Microfluidics”, Biochem. Biophys. Acta, 2013, 1830, 9, 4374-4380.
[3] G. Tarabella, A. Pezzella, A. Romeo, N. Coppedè, P. D&’Angelo, M. Calicchio, M. d&’Ischia, R. Mosca and S. Iannotta, “Irreversible Evolution of Eumelanin Redox States Detected by an Organic Electrochemical Transistor: En Route to Bioelectronics and Biosensing”, J. Mater. Chem. B, 2013,1, 3843-3849.

Solution-gated transistors have shown promising applications in biosensors due to the high sensitivity, low working voltage and the simple design of the devices. Solution-gated transistors normal have no gate dielectric and the gate voltages are applied directly on the solid/electrolyte interfaces or electric double layers near the channel and the gate, which lead to very low working voltages (about 1 V) of the transistors. On the other hand, the devices can be easily prepared by solution process or other convenient methods because of the much simpler device structure compared with that of a conventional field effect transistor with several layers. Many biosensors can be developed based on the detection of potential changes across solid/electrolyte interfaces induced by electrochemical reactions or interactions. The devices normally can show high sensitivity due to the inherent amplification function of the transistors.
Here, I will introduce several types of biosensors studied by our group recently, including DNA, glucose, dopamine, uric acid, cell, and bacteria sensors, based on solution-gated organic electrochemical transistors or graphene transistors. The biosensors show high sensitivity and selectivity when the devices are modified with functional nano-materials (e.g. graphene, Pt nanoparticles) and biomaterials (e.g. enzyme, antibody, DNA) on the gate electrodes or the channel. Furthermore, the devices are miniaturized successfully for the applications as sensing arrays. It is expected that the solution-gated transistors will find more important applications in the future.

Recently, a bio-sensor is required for a home diagnostic, which is an early,simple and reproducible diagnostic. Among bio-sensors, the nanoparticle-organic-memory-field-effect transistor (NOMFET) has been a great interest in biological spiking synapse and cancer-stem-cell detectable biosensor, because it could describe depressing and facilating current behavior and has an large open channel structure easy to attach cancer-stem-cell. In our study, NOMFETs were fabricated with a pentacene channel embedded with Au nanoparticles (50~80 nm in diameter). The 30-nm-thick pentacene channel embedded with Au nano-particles on the gate SiO2 on p++ gate were dipped in a solution of 8-mercaptooctanoic acid in ethanol (1mM) for connecting linker between Au N.Ps and CCSC for 12 hrs, where a CCSC was orginated from Breast Cancer Cell . The threshold voltage shift of the NOMFET was only ~ 0.2 V when phosphate-buffer-saline (PBS) was dropped on the pentacene channel embedded with Au nano-particles. Surprisingly, the threshold voltage shift of the NOMFET was ~ 18 V when the CCSC solution attached anti-body in phosphate-buffer-saline (PBS) was dropped on the pentacene channel embedded with Au nano-particles. This result indicates that the CCSC include the hole charge of 3.1X10-7 C. In our study, we will present the correlation between the CCSC and NOMFET of threshold voltage for shift and drain current in detail. In addition, we test a possibility of the hole charge transfer from Au nano-particles to CCSC to classify the type of cancer stem cells.
* This research was supported by the Converging Research Center Program funded by the Ministry of Science, ICT & Future Planning (Project No. 2013K000283) and Brain Korea 21 PLUS, Republic of Korea.

Organic bio-electronics is emerging as a new discipline involving the study of direct interactions occurring between an electronic device and a biological functional system, such as membrane proteins (ion pumps or receptors) but also DNA, antibodies or enzymes that can act as recognition elements in electronic sensors. The fallout of these studies are generally twofold: to get insights into fundamental issues connected with a bio-system functional properties and to exploit this know-how for conceiving high performing sensing approaches, leading to label-free, sensitive and selective electronic sensors. A review on this topic was recently published by the authors [1].
This lecture will provide an outlook on this field mostly focusing on the study of organic semiconductor (OSC) based field-effect transistors (OFETs) with different device structures. Particular attention will be devoted to the study of different materials serving as gate dielectrics or electrolytes [2, 3]. Indeed, also different biological species that are integrated into the devices to allow for selective interaction with target analytes, will be considered [4, 5]. The devices discussed are also interesting as they can be produced using sub-millimeter scale architectures fabricated by printing compatible procedures, this being a viable route toward low-cost, high performance bio-electronic devices.
[1] L. Torsi, M. Magliulo, K. Manoli, Kyriaki and G. Palazzo; Chemical Society Reviews 42 (22) 8612-28 (2013);
[2] M. Magliulo et al. Advanced Materials 25(14) 2090-2094 (2013);
[3] D. De Tullio et al. Science od Advanced Materials 5(12) doi:10.1166/sam.2013.1658 (2013);
[4] M.D. Angione et al. Biosensors & bioelectronics 40(1) 303-7 (2013);
[5] M. Magliulo et al. Analytical Chemistry 85(8) 3849-3857 (2013).

Charge injection barriers can often be found at electrode-organic semiconductor interfaces. These interfaces play a key role in determining device characteristics and performance. For example, in polymer light-emitting diodes (PLEDs), these barriers can cause imbalanced electron and hole densities and therefore lower the device efficiency. In organic field-effect transistors (OFETs), energetic barriers can determine device parameters such as turn-on voltage, on-off ratios, high contact resistance, and even enable observation of bipolar behavior. In this work, we examined the potential application of DNA as an interlayer to improve charge injection in PLEDs, n-type OFETs, and ambipolar OFETs. Incorporation of DNA interlayers leads to improvements in the transport of PC70BM and ambipolar transport in diketopyrrolopyrrole (DPP)-based OFETs. We attribute these observations to improved charge injection at the Au/organic interface. The field-effect mobility for PC70BM and DPP devices is enhanced together with a reduced contact resistance. For PLEDs, electron injection is improved using a thin layer of DNA between the emissive layer and the Al cathode. The DNA interlayer significantly lowers the device turn-on voltage and increases the luminance efficiency.

Mammalian visual system converts intermittent light signals into discrete nerve impulses and integrate them into a continuous perception of external world through a process termed flicker fusion, which plays a crucial role in perception of object in motion. In bionic visual engineering, the implementation of flicker fusion in artificial visual system still remains challenge. Inspired by the microstructure of the outer segment of rod cell, in which lamellar discs containing phototransduction proteins stacked over an array of tubular cilium for the traffic of mass and nerve impluse, we demonstrate a frequency-responsive photoelelctric nanosystem by reconstituted bacteriorhodopsin (bR) multilayers onto the surface of aluminia nanochannels (AAO) to mimic the flicker fusion process in vitro. Upon the flickering light irradiation from 0 to 130 Hz, a bR membrane thickness dependent optimal flicker frequency (ORF) is identified, at which the amplitude of generated photocurrent reaches its peak value. Beyond this threshold, the photocurrent comes to fuse, analogous to flicker fusion process in rod-mediated vision. Flash kinetics studies reveal that the bR thickness-dependent ORF is dominated by the extended decay time of its long-lived intermediate M412. Under certain cooperative conditions of bR layers, proton concentration gradient and pore size of AAO, the highest frequency-responsive photocurrent was obtained and effectively controlled. Our biohybrid nanosystem effectively reproduces and regulates flicker response in visual perception, which sheds light for the exploitation of artificial vision.

Conjugated polymers (CPs) are multi-chromophoric systems composed of delocalized electrons in alternating σ and π bonds. CPs exhibit light harvesting properties, with absorption and fluorescence properties dependent on polymer chain conformation and aggregation state.Cationic CPs can complex with negatively charged DNA to undergo chain conformation and/or aggregation state charges leading to changes in absorption/emission properties.Colorimetric and fluorimetric DNA biosensing platforms based on cationic water soluble CPs have been demonstrated and they exploit either polymer conformation and/or aggregation state changes induced upon complexation of CPs with DNA or the light harvesting properties of CPs providing amplification via fluorescence resonance energy transfer (FRET) to a dye attached to DNA. However, chemical labeling is expensive and laborious.As the intercalating dyes can only be fluorescent after intercalating into double strand DNA , sequence specificity can be achieved for base mismatch detection.
Here we demonstrate a label free, energy transfer based, sequence specific DNA sensor based on conjugated polymer and intercalating organic dyes.The energy transfer from CPs to intercalating dyes is also studied by a variety of spectroscopic methods.

This talk introduces the use of organic semiconductors as artificial photoreceptors in bio
mimetic devices. The research started some years ago by demonstrating that organic
semiconductors can be used to reproduce the natural retina photoreceptor spectral response
in standard photo-diodes [1]. Second step was the development of hybrid solid liquid photodiodes that can naturally interface with a biological environment through the electronic/ionic interface [2]. The next step was demonstrating that primary neurons (from rat brain) grown on top of a photovoltaic semiconducting polymer acquire light sensitivity [3]. This occurs through a specific mechanism of cell stimulation by polymer photoexcitation (CSP) that will be discussed in the presentation. We then studied explanted retinas put in contact with our organic device. We will show that blind retinas, i.e. retinas with severe damage of the photoreceptors, do regain light sensitivity, as demonstrated by ganglion cell electrical activity upon illumination [4]. The process, its relation to CSP, perspective and future developments will be discussed.

[1] M. Antognazza et al., Appl. Phys. Lett. 90, 163509 (2007)
[2] M. Antognazza et al., Appl. Phys. Lett. 94, 243501 (2009)
[3] Diego Ghezzi et al., Nat. Commun.2,166 (2011)
[4] Diego Ghezzi et al., Nat. Photonics 7, 400 (2013)

Photosynthetic reaction centers (RCs) are protein complexes responsible for solar energy harvesting in bacteria. The high efficiency of these species in achieving charge separation under photo-stimulation has attracted interest in using RCs as a functional unit in bio-solar cells. However, the complexity of the charge transfer between the biological species and the inorganic electrode typically leads to low values of the measured photocurrents in such systems.
A great effort has been done in the last years to optimize the immobilization of RCs on several surfaces making use of suitable linker molecules. Recently, we have suggested that diamond can be an interesting alternative to metal electrodes in these bio-hybrid devices, as it exhibits excellent electrochemical properties and at the same time it provides a suitable surface for covalent immobilization.
In this contribution, RCs from purple bacteria have been immobilized on highly B-doped nanocrystalline and polycrystalline diamond electrodes using various grafting protocols. We have studied the photocurrent signal generated from immobilized RCs enhanced by the presence of cytochrome C, coenzyme Q0 and other redox species in solution. We have found that the role of the first two species in the charge transfer is similar to the role they play in the natural environment of RCs, with cytochrome C shuttling the low-energy electrons from the electrode to the RCs P-side and Q0 extracting the high energy electron from the Q-side of the RCs and shuttling it into the electrolytic solution. A deeper insight into these processes is provided by studying the photocurrent signal as a function of the concentration of these two mediators in solution. We have also investigated the dependence of the photocurrent signal on the voltage applied between reference and working electrode, enabling a deeper understanding of the different steps involved in the charge transfer induced by photo-excitation and how the energetic level of electrodes and redox species can be tuned to maximize the measured photocurrent levels. This work demonstrates recent progress in the use of diamond electrodes in bio-hybrid systems for solar energy harvesting resulting in photocurrent density of the order of 500 nA/cm² stable over several hours of direct exposure to a IR - LED light.

Organic field-effect transistors (OFETs) are highly promising candidates for chemical and biological sensing. Many organic compounds are solution-processable at low temperatures on a variety of substrates, which allows for cost-effective fabrication methods, leading to smart (disposable) sensor tags in the field of health-, food- and environmental monitoring. Concerning the detection of ions or biological molecules in aqueous solutions, a water-stable operation of OFET sensor elements is crucial. Thus low voltage operation is a prerequisite.
In this context electrolyte-gated OFETs (EGOFETs) seem to be the devices of choice. Due to the formation of an electric double layer at the electrolyte/organic semiconductor interface, they exhibit a very high capacitance allowing for a low voltage operation. Moreover, it was reported that devices are stable even if the organic semiconductor is in direct contact with water. Since these transistors are very sensitive to changes of the interface potential they constitute ideal candidates as transducers for potentiometric ion sensors.
Here the realization of ion-selective EGOFETs is discussed. In this context the device stability of poly(3-hexylthiophene) (P3HT) - based EGOFETs on various substrates gated using water and different concentrations of NaCl in water are presented. In order to obtain a sensitive as well as selective response to sodium a commercial available ion selective membrane was introduced and the corresponding interfaces as well as the limiting factors of this ion sensor concept were investigated. The applicability of the sensor is tested in ambient conditions using a broad variety of analytes with and without interfering ions (e.g. different mineral waters).
K. Schmoltner, J. Kofler, A. Klug, and E. J. W. List-Kratochvil, Advanced Materials, DOI: 10.1002/adma.201303281 (2013)
This work was supported by the projects BioOFET 2 and MIEC-DEVs funded by the Amt der Steiermärkischen Landesregierung.

Sensors are devices capable of capturing a certain physical-chemical signal from environment and convert it into a measurable electrical signal by a transducer [1]. Biosensor is a sensor which has a biological sensing element as receptor specific to a particular target analyte [2]. The physical-chemical signals experienced by these devices are converted into electrical signals with proportional magnitude to the concentration of one or more chemical compounds [3]. In this work, we built a pH-sensor using commercial thin films of tin oxide doped with fluorine (FTO) as ion receptor. The sensor was made by linking FTO samples to the gate of a field effect transistor MOS type. In solution, the ions interact with the sample being adsorbed on the surface of FTO film. The potential generated by the ions adsorbed on the film surface modulate the gate voltage of the transistor, in this way, we can determine the concentration of ions present in solution correlated with the magnitude of the transistor response [4]. This kind of device is given the name of EGFET (Extended Gate Field Effect Transistor). The EGFET exhibits sensitivity of 68 mV/pH and linear response in the range of pH 2 to 10. Through enzyme immobilization techniques we could covalently bind urease proteins on the surface of FTO film, changing the pH-sensor in urea biosensor. Buffer solutions with differents pHs and concentrations were tested and was determined that optimal environment conditions for this urea biosensor is buffer solutions with pH = 6 and 10mM of concentration. Under these conditions, the biosensor showed sensitivity of 114.5 mV/p(urea) and linear response in the range of 3,2.10-4 to 3,2.10-2 mol/L.
[1] A. Hulanicki, S. Glab, e F. Ingman, “Chemical sensors: definitions and classification”, Pure Appl. Chem., vol. 63, no 9, p. 1247-1250, 1991.
[2] D. R. Thévenot, K. Toth, R. A. Durst, e G. S. Wilson, “Electrochemical biosensors: recommended definitions and classification”, Biosens. Bioelectron., vol. 16, no 1-2, p. 121-131, jan. 2001.
[3] B. R. Eggins, Biosensors: an introduction. Wiley-Teubner, 1996.
[4] A. Hierlemann e H. Baltes, “CMOS-based chemical microsensors”, Analyst, vol. 128, no 1, p. 15-28, dez. 2003.

Due to the unique physical and chemistry properties, graphene has been viewed as a promising material for fabricating chemical and biological sensors with high sensitivity, chemical stability, and biocompatibility. Solution-gated graphene transistors (SGGT), in which the gate voltage applied on the graphene channel through an electrolyte instead of gate insulator, have been widely studied for detection of biological relevant analytes because the related reactions require aqueous environment.
Whole-graphene solution-gated transistors are designed and realized as high sensitive dopamine sensors. Graphene serve as both the channel and the gate eletrode in the transistor, which provide the possibility for high density integration. Different from previous SGGT-based dopamine sensors, the sensing mechanism is based on the change of effective gate voltage applied on the transistors induced by the electro-oxidation of dopamine at the graphene gate electrodes. The device show high sensitivity with the limit of detection (LOD) of dopamine as low as 1 nM, which is three orders of magnitude lower than conventional electrochemical methods. The interference from glucose, uric acid (UA) and ascorbic acid (AA) on the dopamine sensor is characterized. In order to improve the selectivity of the dopamine sensor, the gate electrode is modified with a biocompatible Nafion film. After the modification, the detection limit of the device to dopamine, uric acid, and ascorbic acid are 1nM, 10 uM and 1 uM respectively, exhibiting excellent selectivity to dopamine.
In conclusion, whole-graphene SGGT-based dopamine sensor with high sensitivity and selectivity was fabricated. The mechanism of functionalizing the gate electrodes for specific detection could be used for developing many other types of biosensors. Therefore the SGGTs have great potential for the applications as low-cost, high density and multifunctional biosensors in future.

The interaction of cell and organelle membranes (lipid bilayers) with nanoelectronics can enable new technologies to sense and measure electrophysiology in qualitatively new ways. To date, a variety of sensing devices have been demonstrated to measure membrane currents through macroscopic numbers of ion channels. However, nanoelectronic based sensing of single ion channel currents has been a challenge. Here, we report graphene-based field-effect transistors combined with supported lipid bilayers as a platform for measuring, for the first time, individual ion channel activity. We show that the supported lipid bilayers uniformly coat the single layer graphene surface, acting as a biomimetic barrier that insulates (both electrically and chemically) the graphene from the electrolyte environment. Upon introduction of pore-forming membrane proteins such as alamethicin and gramicidin A, current pulses are observed through the lipid bilayers from the graphene to the electrolyte, which charge the quantum capacitance of the graphene. This approach combines nanotechnology with electrophysiology to demonstrate qualitatively new ways of measuring ion channel currents.

Unrepaired DNA damage can lead to mutation, cancer, and death of cells or organisms. However, due to the subtlety of DNA damage, it is difficult to sense the repair of damage products with high selectivity and sensitivity. Here, we show sensitive and selective electrochemical sensing of the repair activity of 8-oxoguanine and uracil glycosylases within DNA monolayers on gold by multiplexed analysis with silicon chips and low-cost electrospun nanofibers. Our approach involves comparing the electrochemical signal of redox probe modified monolayers containing the defect versus the rational control of defect-free monolayers. We find sequence-specific sensitivity thresholds on the order of femtomoles of proteins and dynamic ranges of over two orders of magnitude for each target. For 8-oxoguanine repair, temperature-dependent kinetics are extracted, showing exponential signal loss with time constants of seconds. Electrospun fibers are shown to behave similarly to conventional gold-on-silicon devices, showing the potential of these low-cost devices for sensing applications.

Molecular modification of oligothiophene is a topic of intensive investigations for the development of active devices, for example as materials for organic field effect transistors (OFETs) [1-3]. One aspect of its research is the control of HOMO and LUMO energy levels which plays an important role in the stability of organic semiconductors. Accordingly, semiconductors with a first reduction potential ranging from -0.4 to 0.0 V and a first oxidation potential higher than 0.58 V vs SCE are stable in presence of water or oxygen in OFETS devices [4-5]. In other words these potentials are compatible with applications in aqueous media.
Marine biofouling on materials and equipments leads to fatal effects in numerous civil or military marine applications: works in the wide or coastal, sailing ships, running ships, traders and military, offshore platforms, powerboats, aquaculture installations, oceanographic equipments, and optical sensors. Their consequences are estimated at several billion euros a year, including the costs of maintenance. This colonization leads to an increase of energy consumption, a decrease of efficiency and financial losses in particular in the sea transport. Antifouling coatings are used on surfaces in contact with marine fouling organisms [6]. Such coating composition comprises generally polymer matrixes called binders, and biocides which inhibit the settlement of marine organisms. The most successful biocide was for years based on triorganotin compounds. These later are now banned by the International Maritime Organization because of environmental concerns [7].
In this context new concepts of antifouling paint are necessary. In this presentation first results of a new strategy of non-toxic antifouling coatings using organic semiconductors will be presented. The control of redox properties of organic semiconductors on the settlement of marine bacteria will be investigated. In other words it is expected to obtain a bioelectronic control of marine biofouling development.
1. Murphy, A. R.; Fréchet, J. M. J. Chem. Rev. 2007, 107, 1066-1096.
2. Facchetti, A. Mater. Today 2007, 10, 28-37.
3. Mishra, A.; Ma, C.-Q.; Bauerle, P. Chem. Rev. 2009, 109, 1141-1276.
4. Wang, Z.; Kim, C.; Facchetti, A.; Marks, T. J. J. Am. Chem. Soc. 2007, 129, 13362.
5. Jones, B. A.; Facchetti, A.; Wasielewski, M. R.; Marks, T. J. J. Am. Chem. Soc. 2007, 129, 15259-15278.
6. Lejars M.; Margaillan A.; Bressy C. Chem. Rev. 2012, 112, 4347-4390.
7. Kiil, S.; Dam-Johansen, K.; Weinell, C.E.; Pedersen, M.S.; Arias Codolar, S. J. Coat. Tech., 2002, 74(929), 45-54.

Current knowledge in macromolecular engineering allows for the preparation of a myriad of tailored block copolymer morphologies, which play distinguished, multifaceted roles in nanoscience and technology (nanolithography, photonics, pharmaceutical, biomedicalhellip;). Such systems exhibit a remarkable ability to self-assemble into a great variety of supra-macromolecular structures both in solution (nanoparticles: micelles, vesicles...) and in solid state (thick and thin films: lamellae, cylinders, gyroids, spheres...), whose domain spacing span from few to hundred nanometers. Their final nano-organization results from the interaction between the molecular “elementary bricks” and architectures, the block composition or volume fraction and, in the case of solvent annealing, the affinity of the solvent with the different blocks. Most of those systems are, however, derived from petroleum: A resource that is being rapidly depleted!
While the self-assembly of synthetic block copolymer systems is limited today to 20 nm features (domain and size spacing) and in some cases to less than 10nm with “heavy” chemical modification, we have recently developed a versatile hierarchical self-assembly approach of novel multi-functional glycopolymer (carbohydrate) leading by self-assembly process to thin thin films shooting down to few nm-high-resolution nanoscale pattern. Such thin films found a number of key applications, spanning from next generation nanolithography, memory devices, pharmaceutical, biomedical and generally in flexible opto- and bio-electronic devices where the feature size (domain spacing) as well as its control at the 2 and 3D nanoscale level is of great importance.
The talk will focus on the design and the nanofabrication of new hybrid nano-organized thin films made from bio-sourced macromolecules (oligo or polysaccharides) [1-7] for potential applications in “green” flexible electronics. Recent results will be presented on the self-assemblies of sugar-based block copolymer leading to ultra-thin films (sub-10nm resolution) for next generation of flexible opto- and bio-electronic devices.
References
[1] Giacomelli, C., Schmidt, V., Aissou, K. and Borsali, Langmuir 2010, 26, 15734-15744
[2] K. Aissou, I. Otsuka, C. Rochas, S. Fort, S. Halila, & R. Borsali Langmuir, 2011, 27(7), 4098-4103
[3] L.C. Porto, K. Aissou, C. Giacomelli, T. Baron, C. Rochas,.P. Armes, A.L. Lewis, V. Soldi & R. Borsali Macromolecules, 2011, 44(7), 2240-2244
[4] Aissou, K.; R. Borsali, Fort, S.; Halila,T. Baron, Patent (CNRS) 2010, World Extension 2011,
[5] Cushen, JD; Otsuka, I; Bates, CM; Halila, S; Fort, S; Rochas, C; Easley, JA; Rausch, EL; Thio, A; Borsali, R; Willson, CG; Ellison, CJ ACS NANO, 2012, 6, 4 ,3424-3433
[6] Otsuka, I ; Tallegas, S; Sakai, Y; Rochas, C; Halila, S; Fort, S; Bsiesy, A; Baron, T; Borsali, R Nanoscale 2013, 5, 7, 2637-2641
[7] Otsuka, I; Isono, T; Rochas, C; Halila, S; Fort, S; Satoh, T; Kakuchi, T; Borsali, R ACS Macro Letters 2013, 1,12, 1379-1382

In recent years, the bioelectronics field has seen the use of an increasing variety of conducting polymers because they promise to display tunable mechanical properties (flexibility) and the ability to form an intimate interface with living tissue - in strong contrast to their inorganic counterparts [1]. Even though transduction of ionic biosignals into electronic signals is thought to be the key mechanism for successful integration of electronic devices in biological systems, little insight has so far been gained that allows understanding the interplay of electronic and ionic conductivity in the currently employed materials [2]. Here we present a straight-forward and chemically inert materials science approach to this challenge that promises to control mixed ionic/electronic transport in ‘plastics&’ by blending organic semiconductors with insulating polymers. This assists in inducing a more polar nature to the resulting systems and introduces the capability of controlling the interdiffusion of biological media through the final structures. We will demonstrate that electronic transport can be maintained in such multicomponent systems upon blending with the insulating matrix. Moreover, initial studies show faster switching response in large-scale organic electrochemical transistors (OECT) when using blend systems compared to devices fabricated with a single-component conducting layer. This observation suggests that our blend system shows efficient ionic conductivity. We tentatively relate this desirable behavior of the semiconductor:insulator blends to the more polar nature of the latter active layers, introduced through the insulating (commodity) polymers, in addition to the swelling of the blend in the aqueous electrolyte. We thus show that the use of conducting/insulating polymer blends has the potential to bring multifunctionality to the final material systems, including biological activity, biodegradation, topological cues, etc., which in turn promises to enable more specific interactions with biological systems.
[1] R. M. Owens et al., MRS Bulletin, 35, pp. 449-456 (2010)
[2] S. Ghosh et al., Electrochemical and Solid-State Letters, 3 (5), pp. 213-215 (2000)

The diversity of peptides has been exploited in recent years for screening peptides that bind to diverse inorganic materials. Such peptides can be used for directing the synthesis of inorganic nanoparticles. For semiconductors, such surface bound ligands can affect the surface electronic behavior. These electronic effects at semiconductor - peptide interfaces will be the focus of this talk.
First insight into a semiconductor- peptide interface will be obtained using a family of peptides that bind to GaAs (100) [1]. It will be shown that while the "native" peptide, which was previously selected by biopanning methodologies, has only a minor effects on the electronic characteristics of the interface, the introduction of tyrosine or tryptophan amino acids to the sequence greatly modulate the surface work function, both by dipolar contribution and by inducing charge redistribution at the interface. These effects will be shown to depend on the sequence of the peptide. I will further demonstrate that grafting a peptide binder, mutated to include non-natural side chain (porphyrin), on titania results in effective surface photosensitization. Combining this effect with the ability of the peptides to direct the deposition of inorganic films [2], will be shown to result in a room temperature, environmental friendly, deposition of photosensitized TiO2 nanoparticle films. These results demonstrate that inorganic peptide-binders can serve as powerful building blocks for the construction of future electronic devices. In these devices peptides will be used both for the fabrication of the devices, and for controlling their electronic performance.
[1] M. Matmor and N. Ashkenasy “Modulating semiconductor surface electronic properties by inorganic peptide-binder sequence design” J. Amer. Chem. Soc. 134, 20403 (2012).
[2] M. Matmor and N. Ashkenasy, “Peptide directed growth of gold films”. J. Mater. Chem., 21, 968 (2011).

Conducting polymers are rapidly gaining interest as conducting interfaces with biological systems. These materials are inherently advantageous for such applications due to their mechanical properties (“softness”) as well as their ability to conduct both ions and electrons. Several publications have reported the use of conducting polymers in cell-growth and in-vivo applications, whereby the commonly used poly-pyrrole (PPy) is frequently described as bio-compatible. However, PPy has low conductivity and limited stability, which led to the interest in using the conducting polymer poly(3,4-ethyledioxythiophene) (PEDOT). PEDOT:PSS and other versions of PEDOT have been shown to facilitate cell-growth of a number of cell-lines, but - as for most materials - they are not a universal “fit” to all types of cells. Accordingly, it is the well-being of the cells on the PEDOT electrode that must first be addressed in the development of a bioelectronic device. One way to overcome this is by preparing PEDOT composites with materials that are known to promote the growth of the particular cell-line. As an added bonus, this approach may also be a route to enhancing other properties such as conductivity, ion-mobility, hydrophobicity and the ability to obtain direct charge transfer to bio-molecules. Unfortunately, the ability to modify the pre-made PEDOT:PSS is limited due to the instability of the suspension upon addition of extra components.
In this paper, the possibility of incorporating various co-components in and on PEDOT prepared by oxidative polymerisation will be examined - primarily from a materials perspective with a view towards their incorporation into various “bio-applications”.
Our laboratory toolbox includes three main routes through which we can modify PEDOT:
1) Incorporation of macro-molecules during the oxidative polymerisation of PEDOT.
2) A “stuffing" method where the co-components are trapped inside PEDOT by collapsing the PEDOT film after polymerisation (during the washing step where “used” oxidant is removed).
3) Grafting of functional (bio)molecules onto plasma-modified PEDOT.
These methods have been developed over several years, with their details to be given through a number of examples that include the tailoring of PEDOT composites to support growth of “difficult” brain-barrier cells [1], incorporation of enzymes and redox centres into PEDOT for alcohol [2] and pH [3] sensors, enhancing the ion-mobility in PEDOT by addition of hydrophilic polymers that provide ionic “highways” through the composites [4] and the use of functional plasma-polymerised surface coatings on PEDOT as ion selective membranes and as an anchor for simple grafting protocols.
References
[1] Bongo, M. et al. Journal of Materials Chemistry B 2013, 1, 3860.
[2] Winther-Jensen, O. et al. Biosensors and Bioelectronics 2014, 52, 143.
[3] Thompson, B. C. et al. Analytical Chemistry 2013, 85, 3521.
[4] Stavrinidou, E. et al. Under review for PCCP.

The emerging field of organic bioelectronics requires sensing elements for local detection and quantification of relevant species in aqueous and physiological media. In this context, the ability of selectively detect a specific ion is of major interest but still remains a challenge. Conducting polymers combine high conductivity, ion permeability, tunable properties and solution processability, and therefore are ideal transducers for a variety of biosensors. In particular, the mixed electronic/ionic transport properties of conducting polymers can be employed in the development of simple and efficient ion-selective sensors, with application in either environmental or physiological monitoring. Here we present sensing structures based on poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) which, if combined with classical ionophores and ion-selective membranes, is able to selectively determine ion concentration in solution and complex media. Simple polymer electrodes were used for test and optimization of geometry and formulations of the ion sensors. Both polymer/membrane double layer structures and monolithic ionophores-functionalized polymers were explored. These architecture were incorporated into organic electrochemical transistors (OECTs) in order to amplify the signals generated by the concentration gradient at the polymer/membrane interface. We will explore the effect of these parameters on selectivity, sensitivity and detection limit. We demonstrate how OECTs, as ideal ion-to-electron transducer, can be successfully employed in the selective detection of relevant ionic species in aqueous environment.

Organic electroactive materials are increasingly used to produce flexible, low-cost and easily processable electronic devices, such as organic light-emitting diodes, transistors and photovoltaic cells. Recently a great deal of attention is being paid to emerging technologies that exploit the ability of organics to conduct ions in addition to electron and holes. Examples of devices that exploit mixed ionic/electronic transport are: electrochromic devices, light-emitting electrochemical cells, electrolyte-gated transistors and organic electronic ion pumps. Mixed ionic/electronic transport opens exciting scenarios for organic electronic, which has been so far considered mostly as a flexible and low-cost alternative to well-established inorganic semiconductor technologies. In particular, because of the importance of ion fluxes in biology, mixed ionic/electronic transport is the underpinning of the new field of organic bioelectronics, which deals with the coupling of organic electronics with biological systems.
The research of our group focuses on organic electrochemical transistors (OECTs), a class of devices particularly attractive for applications in bioelectronics. OECTs can be operated in aqueous electrolytes as ion-to-electron converters and electrochemical sensors, thus providing an interface between the worlds of biology and electronics. OECTs have been investigated in the last decade as sensors for hydrogen peroxide, glucose, dopamine, chloride ions, cells and bacteria as well as tools to investigate electronic/ionic transport in conducting polymers.
Here we investigate several electrolytes for organic electrochemical transistors and elucidate their effect on device performance. The investigated electrolytes range from aqueous solutions, surfactant, ionic liquids and solid electrolytes. We show how changing the electrolyte might affect device operation speed, modulation and reversibility of the doping/dedoping process.

Organic bioelectronics deals with the coupling of devices based on conducting polymers with biological systems and underpins new technologies, such as implantable electrodes, biosensors and drug delivery systems. Organic electronic materials exhibit mixed conduction: they can transport not only electronic charge carriers but also ions. As such, they offer a suitable interface
between the worlds of solid-state electronics, which use electronic charge carriers, and biology, where signals generally consist of ionic currents.
Among the most common examples of organic bioelectronics devices are organic electrochemical transistors (OECTs). OECTs are able to operate in aqueous solutions at low voltages (< 1 V). They have been used as sensors for hydrogen peroxide, glucose, dopamine, chloride ions, and bacteria. Despite the impressive progress in the field of OECTs, the interrelationships between the chemical composition/morphology of the polymer transistor channel and the transistor
electrical characteristics are still largely unexplored.
In our group we are developping OECTs where the chemical composition and the morphology of the conducting polymer channel is tailored to achieve: i) high current modulation at low operating voltage (ideally 2-3 current decades below 100 mV), and ii) reversibility of the doping/dedoping process taking place upon application of an electrical bias. Such characteristics will improve the ability of OECTs to respond to external stimuli and to reversibly incorporate specific molecules. To achieve this objective, we employed several thin film processing techniques. In particular, we explored spin coating, a combination of screen-printing and vapour phase polymerization and inkjet printing.
By varying the film deposition technique, we are able to obtain films with different morphologies and chemical compositions, which result in different doping/dedoping characteristics. Our work provides new insights on the role of film processing on device performance and offers unprecedented opportunities to clarify the OECT operating mechanism.

Electronic transducers of neuronal cellular activity are important devices in neuroscience and neurology. Organic field-effect transistors (OFETs) offer tailored surface chemistry, mechanical flexibility, and high sensitivity to electrostatic potential changes at device interfaces. These properties make them attractive for interfacing electronics to neural cells and performing extracellular recordings and stimulation of neuronal network activity.
Here I want to present an emerging area of interest where the OFET is used as a gauge to supply a variety of electrical, chemical and electrochemical stimuli to neuronal cells, in an effort to stimulate their plasticity else to differentiate neuronal stem cells into neurons. I will overview the progresses of an ongoing EU project, “Implantable Organic Nanoelectronics” (I-ONE-FP7) which is aimed to the use of organic electronics in implantable devices for the treatment of the spinal cord injury (SCI). The project is presently at midterm, and I will highlight the advances to date and discuss the direction of further development towards in-vivo experiments on animal model of the SCI.
This work involves collaboration of several partners, that I would like to acknowledge through the principal investigators: S. Pluchino (Univ. of Cambridge), M. Berggren and D. Simon (Univ. Linkoeping), F. Zerbetto and S. Rapino (Univ. of Bologna), P. Greco (Scriba Nanotecnologie Srl Bologna), L. Occhipinti (ST Microelectronics Catania), D. Vuillaume (CNRS, Lille), R. Garcia (CSIC Madrid), H. Gomes (Univ. do Algarve), R. Frycek (Amires Sarl, Neuchatel), E. Cerna and V. Velebny (Contipro Dolni Dobrouc), T. Cramer, S. Casalini, F. Valle (CNR-ISMN Bologna), G. Foschi, C. A. Bortolotti, N. Dorigo (UNIMORE).
This work is supported by EU NMP Project I-ONE Grant Agreement n. 280772.

In this work we present an innovative structure for the realization of tactile transducers on flexible plastic substrates. The core of the device is a floating gate Organic Field Effect Transistor (OFET) biased through a control capacitor and with a sensing area directly connected to the floating gate. The floating gate dielectric has been realized by using a combination of two different ultrathin insulating materials (average thickness of 25 nm), composed by alumina (grown on a pre-deposited aluminum film that acts as the floating gate electrode) and Parylene C. Thanks to the high capacitance coupling the fabricated OTFTs can be operated at voltages as low as 1 V. A control capacitor is fabricated on the floating gate and used for setting the operational working point of the sensor. In this way, if an additional electrical charge is somehow induced onto the sensing area fabricated on the floating gate, it leads to a charge separation in floating gate electrode, which, in turns, induces a modulation of the transistor threshold voltage. In order to achieve the sensitivity to pressure, a piezoelectric thin film, namely PVDF-TrFE, is transferred on the sensing area of the device. In this way, when pressure is applied on the PVDF-TrFE, the charges induced in the piezoelectric film, lead to a variation of OFET threshold voltage and a current variation can be detected at each pressure event. We will demonstrate that the fabricated devices are characterized by a reproducible response to applied forces within the range of 0-5 N with a resolution of 0.1 N.
Moreover, PVDF polymer is also characterized by pyro-electric properties, which make it suitable also for the realization of temperature sensors. This feature have been also exploited, and preliminary results on the fabrication and characterization of temperature sensors will be presented. The introduced approach represents a very simple and innovative solution for the realization of multimodal tactile sensing systems on highly flexible and possibly compliant substrates, which could be employed for a wide range of applications in the biomedical field and particularly suitable for the fabrication of artificial electronic skinm

Future biomedical devices may enable chronic sensing or stimulation of body tissue through stable interfaces between soft tissue and high-performance electronics. We demonstrate flexible organic thin-film transistors (OTFTs) on physiologically-responsive smart polymer substrates with shape-changing and softening properties that can mechanically-adapt after implantation for creating soft bioelectronic interfaces while maintain initial electrical properties. Additionally, 3D deployable structures are demonstrated with large geometry changes based on the release of stored applied stresses.
Shape memory polymers (SMPs) are smart polymers which respond to stimuli, such as a temperature change, to soften and change shape. We synthesize SMP substrates which can adapt in vivo to autonomously form secure interfaces with target tissue via a two order of magnitude drop in modulus when exposed to physiological conditions, which reduces the modulus mismatch between the device and soft tissue. Reduction in the mechanical mismatch between biomedical implants and soft tissue through soft materials has been shown to extend the long-term viability of biotic/abiotic interfaces. Acute in vivo stability of an OTFT which adapts to the morphology of soft tissue is shown, with only small changes in device performance after implantation for 24 hours. OTFTs fabricated on SMP substrates are demonstrated which can autonomously deploy to programmed 3D shapes 15× larger than the insertion footprint of the device, as well as conform to 3D surfaces with radii as small as 500 µm when triggered by a small temperature change. Flexural stability of the OTFTs is demonstrated down to 1 mm radius for four bending configurations; with some devices remaining operational at radii as small as 100 µm. The flexible low-voltage transistors (2 V) based on the air-stable organic semiconductor, dinaphtho[2,3-b:2&’,3&’-f]thieno[3,2-b]thiophene (DNTT), are demonstrated with a measured average mobility of 1.5 cm^2V^-1s^-1 and an on/off current ratio of 10^4, which is suitable for sensing small biosignals at low operating voltages.

In this talk I will discuss our recent progress in designing new materials, sensors and integrated devices for electronic skin applications. We have been working with a variety of electronic materials to add new functionality and increase stretchability. We have developed ultrasensitive and stable organic transistor sensors for chemicals and biological species. We have also developed multifunctional devices to enhance the versatility of electronic skin.

Implantable medical devices have made a major impact in improving healthcare. Increasingly in recent years, devices have become active rather than passive - for example cardiac pacemakers. A key challenge for these active systems, as well as for others on the horizon is their need for an internal electrical power source. A downside of present systems is the limitation of internal batteries, which must be changed frequently, requiring follow-up surgical procedures, with associated complication risks and additional healthcare costs. One compelling solution would be to employ energy harvesting as a means of recharging or completely replacing batteries. Energy harvesting, through chemical reactions, heat extraction, blood flow, and natural mechanical movements of organs, could help address energy depletion in implants. However, most harvesting units being considered today are like conventional batteries, in that they also rely on rigid electronics and subcomponents, and therefore, are incapable of providing intimate mechanical contact with soft tissue.
In this study, materials and devices that enable high efficiency mechanical to electrical energy conversion from the natural contractile and relaxation motion of the heart, lung and diaphragm, demonstrated in several different animal models, each of which has organs with sizes that approach human scales are reported. A combination of such energy harvesting elements with rectifiers and microbatteries provides an entire flexible system, capable of viable integration with the beating heart via medical sutures and operation with efficiency of ~2%. Additionally, in vitro experiments, computational models and results in multilayer configurations capture the key behaviors, illuminate crucial design features and provide sufficient power outputs for operation of pacemakers, with or without battery assist. The key findings consist of in vivo demonstrations of ultra-thin lead zirconate titanate (PbZr0.42Ti0.58O3, PZT) based energy harvesting devices on flexible polyimide substrate (i) with output open-circuit voltages and short-circuit currents that are greater by three and five orders of magnitude, respectively, than previous in vivo results; (ii) monolithically integrated with rectifiers and millimeter-scale batteries for simultaneous power generation and storage, including high power, multilayer designs; (iii) in biocompatible forms, evaluated through cell cultures and large-scale, live animal models, on various locations/orientations on different internal organs; (iv) for harvesting inside the body, via open and closed left thoracotomy experiments with a bovine model.

Wearable bio-sensor systems will play a vital role in the emerging next-generation healthcare systems, clinical diagnoses and daily monitoring due to their integration flexibility and mobility on physiological signal measurements. Traditional bio-medical sensors have planar metal electrodes and rigid wiring that experience poor signal quality and ineffective electrode to skin contact, many restrictions are hence imposed to disable long term monitoring due to the lack of subject mobility. We demonstrated wireless, flexible and stretchable skin-mounted epidermal sensor systems that conformably laminate on human skin for impedance sensing through near-field coupling method. Skin impedance value can be interpreted into skin hydration level through calibration.
Wireless passive sensing of epidermal sensors is based on capacitive detection through inductive coupling method: the changes in the secondary components will alter the resonance frequencies of primary circuits made of inductors and capacitors. This approach potentially offers simplification in sensor design and eliminates the need of battery use to enable mobile daily health monitoring system.
The system presented is capable of quantifying dielectric and strain changes of the skin. Skin dielectric measurements can be related to physiological, dermatological and cosmological processes as an effective diagnostic tool. Strain sensors can provide complementary data to the above measurements. Other sensing techniques for temperature, pH and humidity can also be integrated in a similar wireless epidermal system.