In neutral aqueous environment, we fabricated strong thin films from graphene oxide that are physically crosslinked by silk fibroin, and demonstrated modifying the surfaces of the films with controlled depth of chemical reduction. These films were treated by placing aluminum metal as reducing agent on designated surface areas, where the conversion from graphene oxide to reduced graphene oxide was thermodynamically driven. The electrical conductivity of the nanocomposite can be tuned by either the concentration of the silk fibroin or the ion-induced reduction time. After being reduced, the graphene oxide - silk fibroin nanocomposite film exhibits 1260 S/m effective conductivity and the elastic modulus increased to 20 GPa. The unique sandwiching structure of the conductive and the insulating layers of the nanocomposite films makes them possible to fabricate stacking all-carbon electronic devices. Moreover, due to the biodegradability of silk fibroin crosslinker, it is a suitable candidate for biodegradable flexible electronic devices. With this environmentally friendly and facile strategy, almost all graphene oxide based nanocomposite films can be readily modified and integrated into electronic applications while maintaining their functional and structural robustness.

We have demonstrated the use of vertical phase separation to speed up ion modulated organic transistor manufactured on rough and recyclable paper substrates. We have shown that by using a blend of a biodegradable PLLA with the semiconductor P3HT we solve two main problems with making paper electronics from organic semiconductors, namely the semiconductor becomes thin and separated from the paper substrate. We can then obtain lower off-currents and faster operation, as demonstrated with the four orders of magnitude increase in operational speed of the OFETs on paper. Our ring oscillators are also one of the first to be fabricated on paper not coated with plastic.

Neural interfaces with high sensitivity and selectivity are an essential tool to expand our knowledge in neuroscience and to develop therapeutic solutions in neurodegenerative diseases and neuroprosthesis. The latter involve electrodes designed to communicate bi-directionally with the central or peripheral nervous systems. Furthermore the efficiency of the neural electrode interface rests on its ability to intimately conform the structure of the biological tissue and, in some cases, endure the extreme mechanical strain inherent in the neurological tissues, e.g. nerves and the spinal cord.
We demonstrate that mechanically compliant polymers combined with scalable microfabrication techniques can be used to batch-produce implants with improved biomechanical compatibility and improved electrode characteristics (compared to state-of-the art platinum ones).
Using electrodeposited PEDOT coatings on thin-film metal electrodes embedded in silicone rubber, we report a reduction of up to 20 times of the electrode impedance at 1kHz, an increase in charge storage capacity of up to 17 times and a dramatic increase in maximal charge injection capacity to 20 times, compared to uncoated electrodes. The soft electrode arrays can also withstand significant mechanical bending, twisting and stretching without impairing their electrical specifications.
We will further illustrate the potential of this technology in the context of auditory brainstem implants and spinal cord neuroprosthesis.

The talk will give a brief review of latest work in the diverse areas of macroelectronics, soft robots and energy harvesting. Macroelectronics is a recent branch of electronics mainly driven by research on large area displays. Based on initial work on large area position sensitive detection schemes with cellular polymers and organic photodiodes, solutions were developed to make any large area screen interactive, techniques currently being commercialized. Organic semiconductors are still an active area of research, with new developments in the identification of highly unusual material systems. Hydrogen bonded analogues of tetra- and pentacene, epindolidione and quinacridone show large field effect mobilities and stable hole transport in air, questioning the necessity of strong intramolecular pi-conjugation for efficient charge transport. Epindolidione and quinacridone are better known as yellow and magenta colors in ink-jet printers. Ultrathin and lightweight organic solar cells with high flexibility are over ten times thinner, lighter and more flexible than any other solar cell of any technology to date.
They reversibly withstand extreme mechanical deformation and have unprecedented solar cell-specific weight, with potential applications in stretchable electronics, the latest frontier of research in macroelectronics. While solar cells deliver energy, energy must also be stored for stand alone stretch electronic systems. Ultrastretchable dry gel cell battery, able to withstand mechanical stretching up to 100 % have been developed by several groups. Ultrathin electronics with a total thickness of around 2 mu;m allows bending with a radius of 5 mu;m. Such electronic foils can be even crumpled without failure and may pave a way for imperceptible electronics. Stretchable electronics relies on elastomers. When an electric field is applied to soft elastomers, the thickness decreases and the area expands. This simple and robust principle is used in soft robotic systems, and most recently also in energy harvesting of mechanical energy from human gait or ocean waves. Voltage triggered area expansions of 1700 % in dielectric elastomer membranes, as well as tools for analyzing the efficiency of dielectric elastomers for the conversion of mechanical into electrical energy mark latest developments in the field.
I hope the talk will show that soft materials developed from scientific curiosity to real world applications.
Work supported by the Austrian Science Funds and by the European Research Council within the Advanced Investigators Grant "Soft-Map".

Imperceptible electronic sensor foils that can be integrated directly into or onto soft materials such as biological tissue or textiles enable innovative applications spanning medical, safety, security, infrastructure, and communication industries among many others. Sensors and actuators for health care and monitoring require electronics to be thin, highly flexible and lightweight in order to minimize patient discomfort.
Here we report large area active matrix tactile senor foils only 2 µm thick that are 27-fold lighter than office paper, can be crumpled like paper and operated at elevated temperatures and in aqueous environments. High-performance organic thin film transistor arrays integrated directly onto 1.2 µm thick polymer substrates exhibit excellent carrier mobilities of 3 cm2/Vs and are operated at only 3V. A hybrid oxide gate dielectric enables extreme mechanical resilience that allows our electronic foils to be bent into radii of 5 µm and less and form an intimate contact with arbitrary shapes including human skin. In bio-medical applications, including in-vivo sensing of bio-signals, ultrathin electronic foils must operate at elevated temperatures and in aqueous environments. At just 2 mu;m thickness our devices exhibit remarkable environmental stability, withstanding thermal annealing up to 170 °C and remain fully functional when completely immersed into salt water and continuously operated for more than two weeks.
Together with polymer light emitting diodes and organic photodetectors, active matrix transistor arrays provide a sensor and actuator platform for ultra-conformable and imperceptible electronic circuit foils as electronic skin, for bio-medical monitoring and treatment systems or smart packaging.

Many natural chromophores feature intra- and inter-molecular hydrogen bonding. Our motivation for exploring such molecules is the realization of biodegradable and biocompatible electronics fabricated from cheap and nontoxic materials. We find that pigment-forming dye molecules such as indigos, tyrian purple, and quinacridones form highly-ordered thin films with excellent pi-stacking. Using such films, we have demonstrated field-effect transistors and complementary-like circuit elements utilizing exclusively natural materials operating at the state-of-the-art level with respect to mobility and operational stability in ambient conditions. These dyes show air-stable ambipolar charge transport with balanced hole and electron mobilities in the range of 1×10-2 - 2 cm2/Vs. Such performance places these molecules among the best organic semiconducting molecules reported to-date. Hydrogen-bonding causes strong intermolecular electronic coupling, resulting in optical properties dominated by excimeric and charge-transfer effects. We exploit these properties to fabricate single-layer metal-insulator-metal solar cell diodes that show high photocurrent yields usually thought to be accessible only with the use of donor-acceptor heterojunctions. We discuss also preliminary experiments concerning field-effect transistor biodetectors based on these materials. Hydrogen-bonded natural and nature-inspired materials are an interesting and previously unexplored class of organic semiconductors with inherent potential for biointegrated applications.

Many biological processes involve ion translocation across cell membranes that are carried out by membrane proteins. Bacteriorhodopsin (bR) acts as a photoactivated model proton pump which can generate transmembrane potential, which makes it an attractive candidate for use in bioelectronic devices. We use template-driven assembly to incorporate bacteriorhodopsin molecules in the nanowire transistor to create a hybrid nanobioelectronic device that converts photocycle events into an electrical response. In this presentation we will discuss preparation, characterization, and overall performance of these devices. We will also present examples where adding other biological molecules to this integrated system allowed us to vary some device operational characteristics. This research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences.

One of the great goals of science and engineering today is to develop rapid, accurate, and portable diagnostic technologies for the prevention of infectious diseases such as syphilis and acquired immune deficiency syndrome (AIDS). It has been estimated that 30minus;36 million people globally are living with human immunodeficiency virus (HIV)/AIDS and cannot survive more than two years. Therefore, accurate and rapid HIVminus;2 antibody (Ab) diagnostic testing is challenging because there is no cure or established primary preventative measure. Although various approaches for detecting HIVminus;2 Ab have been developed with some advantages, a novel methodology is still needed to overcome their limitations such as time-consuming, poor efficiency, highminus;cost, low sensitivity, and the need for preparation of the post-clinical setting.
Graphene has attractive physical/electrical properties including extremely high mobility and capacity, and a tunable conductance. From these advantages, the reduced graphene oxide (RGO)minus;based biosensors have been developed that have large detection areas and unique electronic properties. Although, RGOminus;based biosensors have displayed sensitive and selective signals, they have critical limitations such as structural unreliability and performance degradation in electrical sensing devices. Moreover, the minimum detectable level (MDL) is too high compared with conventional biosensors because of irregular shape of RGO, presence of wrinkles on the RGO surface, and low purity from uncompleted oxidation of GO. To realize highminus;performance grapheneminus;based biosensors with better sensitivity and selectivity, the following issues need to be considered in the material design: i) a high-quality graphene with superb electrical/physical properties, ii) a greater surface area for enhanced receptor/analyte interactions, and iii) efficient synergistic effects between the hybridized nanomaterials.
In this work, we establish flexible large-scale GM nanobiohybrids with close-packed carboxylated polypyrrole nanoparticle (CPPyNPs) arrays. Specifically, they were utilized as highminus;performance transducers in a liquid ion gated fieldminus;effectminus; transistor (FET)minus;type HIV immunoassay as an easy and portable pointminus;ofminus;care. Importantly, the flexible GM substrates were integrated with microfluidic channels to improve analytical performance in a living system. Fieldminus;induced sensitivity from liquid ionminus;gated FETminus;type HIV immunosensor was observed, eventually leading to the recognition of a target HIV biomarker at an unprecedentedly low concentration. Notably, the GM nanobiohybrid HIV immunosensor had the lowest detection limit of 1 pM (signalminus;tominus;noise ratio: 5.7), which is 1minus;2 orders of magnitude more sensitive than previously reported HIV sensors. To our knowledge, this is the first experimental demonstration of a largeminus;scale flexible fluidic FETminus;type HIV immunoassay using highly ordered GM nanobiohybrids combined with closeminus;packed conducting polymer nanopartticles arrays.

Membrane proteins represent an interesting and promising part of the bionanoelectronic toolkit because of the many important functions that they perform in living cells. 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 nano-bioelectronic device that can convert proton and ion transport and ion channel gating events into electrical signals. This presentation will discuss several realizations of these devices that use passive ion channels and ATP and light-driven pumps, as well as potential uses of other biological components to alter the device characteristics. This research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences.

Continuous advances in organic electronics and studies on odorant binding proteins present in mammalian nose is stimulating research on Organic Field Effect Transistors (OFET) based e-noses or e-tongue [1]. Odorant molecules such as Carvone and Pyrazines are widely used as artificial flavoring agents in food materials. Detection of these odorants is of great interest in determining food quality. Considerable work has been done on detecting odorants in gaseous media, while detecting odorants in liquid media using OTFTs is still being explored. Recent demonstration of electrolyte/water gated field effect transistors (EGOFET) for sensing applications has opened new doors for sensing analytes in liquid media [2]. To enhance sensitivity and selectivity of EGOFET to target molecules, bio-molecules or soluble proteins such as odorant binding proteins (OBPs) specific for the analyte to be detected can be incorporated in EGOFET architecture. OBPs can be integrated into or on the active semiconducting area or dielectric. Consequently, change in device performance can be detected due to analyte - OBP interaction.These methods have adverse influence on device performance. To further increase sensitivity of EGOFET employing analyte specific OBPs without modifying active semiconductor layer or dielectric layer, another approach is to detect change in work function of gate electrode due to changes in surface charges caused by odorant - OBP interaction. Work function being inherently surface property, allows detection of minute variations in charges on the surface of electrode enhancing the sensitivity of the sensor. These changes in work function consequently affect change in threshold voltage of the transistor. This threshold voltage shift can be used as a sensing parameter for EGOFET based odorant sensor.

We present biosensor based on an electrolyte gated OFET fabricated on flexible substrate with OBPs immobilized on gate electrode. Pig OBPs were immobilized on gate electrode using self-assembled monolayers having different chain lengths. Carvone was selected as an analyte due to its strong binding affinity with pig-OBP as determined by competitive fluorescent binding assay. Solubility of carvone in water was determined by UV-Vis spectroscopy. Elemental composition before and after bio-functionalization of gate electrode with OBPs was determined by X- ray photo-electron spectroscopy (XPS), and fluorescent imaging was used to confirm attachment of bio-molecules on the gate electrode. Carvone concentrations in pico-molar range were successfully detected. These biosensors have potential applications in low cost low voltage disposable sensors for food quality control and monitoring.
[1] L. Torsi, A. Dodabalapur Anal. Chem., 70, 381A-387A (2005).
[2]M. Magliulo, M. Mallardi, M.Y. Mulla, S. Cotrone, B.R. Pistillo, P. Favia, I. Vikholm-Lundin, G. Palazzo and L. Torsi, Adv. Mater. 25 (14), 2090-2094, Apr. (2013).

The field of organic bioelectronics, where a bio-recognition element is interfaced with an electronic device, has drawn a lot of attention in the last years and new bio-sensing platforms capable of rapid screening of biological samples have been explored. These sensors besides potentially interesting in point-of-care applications can be used in several analytical sectors. Particularly, the integration of specific bio-receptors for the analyte of interest could enhance the selectivity and the sensitivity of the electronic device. However, the design and fabrication of a bio-sensing electronic platform stable in liquid media, offering good sensitivity and selectivity, and with low power consumption is still a big challenge. The key point is the development of electronic device in which the bioactivity of the recognition element and the electrical propriety of the transducing element are retained. To this aim interesting is the electrolyte gated EGOFET configuration [1, 2] incorporating bio-recognition elements, were recently developed by our research group. [3]
In this work we propose the use of a biopolymer, in direct contact to the organic semiconductor, as matrix to incorporate bio-recognition elements in EGOFET devices. Specifically, a water soluble polymer was investigated for immobilization of bio-molecules by entrapment and as gating material.
[1] Kergoat, L., B. Piro, M. Berggren, M.-C. Pham, A. Yassar, and G. Horowitz, Org. Electron. (2012), 13, 1.
[2] Khodagholy, D., V.F. Curto, K.J. Fraser, M. Gurfinkel, R. Byrne, D. Diamond, G.G. Malliaras, F. Benito- Lopez, and R.M. Owens, J. Mater. Chem. (2012), 22, 4440.
[3] Magliulo, M., A. Mallardi, M.Y. Mulla, S. Cotrone, B.R. Pistillo, P. Favia, I. Vikholm-Lundin, G. Palazzo, and L. Torsi, Adv. Mater. (2013), 25, 2090.

Biosensors based on organic thin film transistors have attracted much attention recently for many advantages including easy fabrication, low cost, high sensitivity, good mechanical flexibility and biocompatibility. Organic electrochemical transistors (OECT), a type of organic thin film transistor, can operate in electrolyte with stable performance and low voltages, and are thus excellent candidates for high-performance biosensors. In this talk, I will firstly introduce the working principle of the OECT-based biosensors. Then two types of devices recently developed in our group with different sensing mechanisms will be introduced. One type is the devices with functionalized gate electrodes that have been successfully used in DNA, glucose, dopamine and uric acid sensors. Another type is the sensors based on the interactions between the organic channel and the analytes, which include cell-based biosensors, bacteria and ion sensors. In the end, conclusions and perspectives will be addressed.

The natural colonization of organisms such as bacteria or invertebrates on submerged surfaces is known as Biofouling. This process plays a negative role in several fields, ranging from the medical implant design (e.g., stents, catheters, prostheses) to the marine biofouling (colonization of submerged substrata by marine bacteria) to industrial implants as pipelines and aquaculture facilities.
In order to achieve control of bacterial adhesion and biofilm formation, we developed a measurement system based on conducting polymer films. This class of materials is already widely used for biomedical and biosensing applications, allowing for biocompatibility, low cost and tunability of their properties.
In this work we first describe the fabrication of a device by means of an innovative photolithographic technique. The modification of the oxidation state of the conducting polymer in contact with bacteria is achieved by electrochemical switching, both statically and dynamically, and a bacteria adhesion bioassay was performed, allowing for quantification of the bacterial biofilm formed as a function of the surface properties. Results of surface-dependent adhesion are presented and discussed.

The use of conducting polymers as materials for bioelectronics is a rapidly-growing research field. Their mechanical and electrical properties, together with their excellent biocompatibility, make them more suitable for being used as an interface between electronics and cell tissues than “traditional” inorganic semiconductors. Moreover, the fact that the electronic properties of conducting polymers can be modified in response to electrical stimuli creates the opportunity to use these materials as active substrates for cell growth.
Recently, conducting polymers were proved to influence cell behavior, in terms of cell adhesion and growth, by a change in their oxidation state [1-3]. The cell-substrate interaction involves many different parameters, both physical (surface roughness, surface energy), chemical (pH, surface oxidation state) and biological (extra-cellular matrix formation, protein conformation), but the way these parameters are related to each other and to cell behavior is still not clear. Gaining a better understanding of the processes that control cell adhesion is crucial in order to use conducting polymers as a new tool in basic research, medical diagnostics, and tissue engineering.
We employed three different techniques, spin-coating, electro-polymerization and inkjet printing, to deposit thin films of a bio-compatible conducting polymer widely used in organic electronics, poly(3,4-ethylene dioxytiophene) doped with poly(styrenesulfonate) (PEDOT:PSS). These techniques impart quite different physical and chemical properties to the films, namely surface roughness, electrical conductivity, and redox-state. We characterized the effects of these deposition methods by atomic force microscopy, optical absorption, electrical and electrochemical analyses.
Finally, we studied the effects of cell adhesion and proliferation on the PEDOT:PSS films by growing primary human dermal fibroblasts (hDF) cell culture. The cells were kept in a CO2 incubator while cell adhesion, proliferation and tissue formation were on line monitored for a time interval up to 168h (seven days) by automatized optical microscopy.
[1] A. M. D. Wan et al., Adv. Mater. 2012, 24, 2501-2505.
[2] A. Gumus et al., Soft Matter, 2010, 6, 5138-5142.
[3] C. Saltograve; et al., Langmuir, 2008, 24, 14133-14138.

Functional nanowires and nanoelectronics are sought for their use in next generation integrated circuits, but several challenges limit the use of most nanoscale devices on large scales. DNA has great potential for use as a molecular wire due to high yield synthesis, near-unity purification, and nanoscale self-organization. Nonetheless, a thorough understanding of ground state DNA CT in electronic configurations under biologically relevant conditions, where the fully base-paired, double-helical structure is preserved, is lacking. We explored the fundamentals of charge transport (CT) through double-stranded DNA monolayers on gold by assessing 17 base pair bridges at discrete points with a redox active probe conjugated to a modified thymine. This assessment is performed under temperature-controlled and biologically relevant conditions with cyclic and square wave voltammetry, analyzing the redox peaks to assess transfer rate and yield. We demonstrate that the yield of transport is strongly tied to the stability of the duplex, linearly correlating with the melting temperature. Transfer rate is found to be temperature-activated and to follow inverse distance dependence, consistent with a hopping mechanism of transport. These results establish the governing factors of charge transfer speed and throughput in DNA molecular wires for device configurations, guiding subsequent application for nanoscale electronics.

Graphene is considered promising for bio-sensors based on field effect transistors (FETs) because its electrical conductivity can be modified through interaction with chemical or biological species. The higher electrical sensitivity of these devices is related to the number of graphene sheets and their quality. However, the development of sensors based on graphene in large arrays employing arbitrary substrates, such disposable devices on plastic has yet to be demonstrated. In this work, we report the achievement of large area, few-layer graphene films produced by chemical vapor deposition (CVD) process and their implementation into arrays of FETs on plastic and SiO2/Si substrates towards applying them for sensing biological molecules. The graphene films obtained by CVD were transferred onto the desired substrates, achieving uniform coverage on the entire four-inch wafer surface. The assembled few-layer graphene films were configured as chemiresistors by employing a conventional photolithography step followed by metal (Ti/Pd and Ti/Au) deposition and formation of source and drain electrodes by lift-off process. In a single step, over 3,000 devices were produced. After passivating the electrodes, only the graphene channels between source and drain electrodes were exposed to the environment. The devices were then electrically characterized in air and in buffered solutions at different pH and ionic strength values. For the measurements in solution, an ionic liquid gate configuration was employed. Our results suggest that our method allows massive number sensor devices to be fabricated through a simple, fast and scalable approach.

Photoconversion membrane proteins (MPs) are Nature&’s nanoengineering feats for renewable energy management. Harnessing their functions in synthetic systems could help understand, predict, and ultimately control matter and energy at the nanoscale, which is particularly enticing in the post-genome era as recombinant or cell-free expression of many MPs with high yields becomes possible. However, the labile nature of lipid bilayers renders them unsuitable for use in a broad range of engineered systems. A knowledge gap exists on how to design robust synthetic nanomembranes as lipid-bilayer-mimics to support MP functions, and how to direct hierarchical MP reconstitution into those membranes to form 2-D or 3-D ordered proteomembrane arrays. Our studies on proteorhodopsin (PR) and bacterial reaction center (BRC), the two light-harvesting MPs that convert solar energy into two basic forms of matter transport, i.e., proton pumping and electron-hole separation, respectively, reveal a charge-interaction-directed reconstitution (CIDR) mechanism, which induces spontaneous reconstitution of detergent-solubilized MPs into various amphiphilic block copolymer membranes, many of which have far superior stability than lipid bilayers. Our preliminary data also suggest MPs are not enslaved by the biological membranes they derive from; rather, the chemically nonspecific materials properties of MP-supporting membranes may act as allosteric regulators. Versatile chemical designs are possible to modulate conformational energetics of MPs, hence their transport performance in synthetic systems.

Future biomedical devices may enable chronic sensing or stimulation of body tissue through high-performance electronics with stable interfaces to target tissue. We demonstrate flexible organic thin-film transistors (OTFTs) on physiologically-responsive smart polymer substrates with shape-changing and softening properties that can provide additional functionality over typical flexible substrates. These OTFTs 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. Bending 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.
Adaptive OTFTs are facilitated by a thiolene-acrylate shape memory polymer (SMP) substrate, which exhibits a drop in modulus of over two orders of magnitude when ambient temperature exceeds the glass transition temperature (T_g). This enables large shape changes based on the release of stored applied stresses for creating deployable structures, or the conforming of films to 3D geometries. Reduction in the mechanical mismatch between biomedical implants and soft tissue has been shown to extend the long-term viability of biotic/abiotic interfaces. SMP substrates are synthesized with a T_g near body temperature which could enable devices which adapt in vivo to autonomously form soft, secure interfaces with target tissue. 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 cm²V^-1s^-1 and an on/off current ratio of 10⁴. Conforming OTFTs are fabricated directly on the SMP substrate, while deploying OTFTs are created by polymerizing an SMP film on top of OTFTs fabricated on a 1 µm PET film. These high-performance, air-stable OTFTs on physiologically-adaptive substrates that conform and autonomously change shape could have applications in bioelectronics for chronic sensing or stimulation of soft, dynamic and curvilinear tissue.

Rapid and precise discrimination among various odorants is a challenging research subject for key applications in the fields of foods safety, environmental monitoring, and disease diagnosis because odorants can differ by only a single carbon atom in their structures. The olfactory system in humans or animals is capable of recognizing specific odorant compounds at very low concentrations (as low as parts per trillion: ppt). Up to date, several studies such as surface plasmon resonance, quartz crystal microbalance, and light-addressable potentiometric sensors, have been introduced for developing artificial olfactory devices. Unfortunately, although each of these methods has individual strengths, significant limitations including low sensitivity, slow response times, and limited portability remain. Moreover, no flexible and transparent olfactory systems are currently suitable for flexible electrical devices.
Graphene, composed of single-atom-thick of sp2-hybridized carbon, that has attracted tremendous attention because of extraordinary thermal, mechanical, and electrical properties. Especially, devices using grahene have shown high carrier mobility at room temperature. Based on these superior characteristics, the graphene has emerged as valuable platform for a wide range of applications such as electronic devices, energy storage, solar cells, display devices, and chemical/biological sensors. However, its applications, notably in On/Off switching devices, have limitation owing to the absence of a band gap. Accordingly, a number of approaches to assign it semiconductor properties have been proposed by substituting carbon atoms with foreign atoms or transforming into nanoribbons and nanomesh. Nevertheless, most of these methods are limited by the use of complex process at high temperature for a long time
In this presentation, we report an ultrasensitive and flexible field-effect transistor (FET) olfactory system, namely, a bioelectronics nose (B-nose), based on modified bilayer graphene (MBLG) integrated with hOR2AG1 human olfactory receptors, which can bind with a specific odorant. The graphene was treated with oxygen and ammonia plasma to control the bandgap. It showed stable p-type (oxygen plasma-treated graphene; OG) and n-type (ammonia plasma-treated graphene; NG) behaviors, which are suitable for FET-type devices. Importantly, the liquid ion-gated FET-type B-noses with OG had the lowest detection limit, as low as ca. 0.04 fM (10minus;15), which is ca. 2 orders of magnitude more sensitive than previously reported olfactory sensors. Additionally, the B-nose displayed long-term stability and had excellent mechanical bending durability in flexible systems. To the best of our knowledge, this is the first example of a high-performance flexible and transparent FET-type B-nose based on a modified bilayer graphene-conjugated olfactory system.

In the last years Organic Field-Effect Transistors (OFETs) have attracted much attention in sensing applications thanks to the capability of the employed organic semiconductor (OSC) to act both as electronic transport and sensing layer [1]. The integration of biological receptors can endow the device of suitable selectivity properties. Even though many methods for bio-molecules immobilization exist, the integration of bio-receptors on the active area of OFETs remains a challenge. In the present work, an OFET based biosensor selective for the C-reactive protein (CRP) was developed. The anti-CRP antibody was deposited on the poly(3-hexylthiophene) (P3HT) organic semiconductor surface of Electrolyte Gated Organic Field Effect Transistors (EGOFETs) [2]. The deposition strategy involved at first a radio frequency Plasma Enhanced Chemical Vapour Deposition (PE-CVD) process generating a hydrophilic polymeric coating [3]. Biotinylated phospholipids bound to this coating, furnish the binding sites for streptavidin or avidin proteins that are then used to immobilize the biotinylated anti-CRP antibody layer able to specifically capture the CRP. All the transistors were tested using PBS 10 mM as electrolyte gate dielectric before and after the incubation of the CRP. The results indicate a good selectivity and the sensing mechanism is presently under investigation.
[1] L. Torsi, Analytical Chemistry 77 (2005), 380-387
[2] M. Magliulo, Advanced Materials (2012), DOI:10.1002/adma.201203587
[3] M. Magliulo, Plasma Processes and Polymers 10 (2012), 102-109

With growing interest in one-dimensional (1D) nanomaterials such as nanowire or nanotube due to their various powerful applications, ranging from molecular nanoelectronics to energy devices, the orientational control and arrangement of these materials are considered as a significant issue that determines the performance of devices. In addition, the structural design of anisotropic nanomaterials has provided scientific understanding for unveiling unique properties. However, these geometrical designs need to meet conditions of narrow size distribution and suitable aspect ratio for controlling the structural characteristics. Moreover, many conditions are to be optimized for obtaining highly ordered and close-packed nanostructures. Among various controlling factors, the binding affinity between 1D nanomaterials and underlying support matrix is also important.
In this presentation, we propose a novel method for creating unidirectional orientation of close-packed monolayer of one-dimensionally-shaped M13 viruses using a neutral surface of graphene. As a templating biomaterial, M13 virus is adopted due to its structural homogeneity and ease of manipulation. To fabricate unidirectional and closed-aligned viruses on the underlying matrix, we employed chemical vapor deposited (CVD) graphene surfaces, which exhibit excellent electrical conductivity and ideally flattened surface condition. The genetically engineered M13 virus, which enables interaction with graphene via aromatic pi-pi interaction, can manipulate liquid-crystal behavior of virus, determining the orientation and assembly density. Then, peptide-mediated biomineralization or binding from two-dimensionally ordered virus scaffold enable the assembly of dense, highly ordered Au nanoparticles or WO₃ nanowires along surface proteins of the M13 virus. By using such nanostructures, we conducted research on organic photovoltaic devices as inter-layer and electrode. In this structure, virus-templated Au or WO₃ inter-layer could provide enhanced light absorption or efficient hole-injection properties on graphene electrode. We observed that device performance was better compared with conventional nanostructures. Furthermore, these approaches can also provide tool for the construction of various functional materials on graphene film.

Interest in the biodegradability of natural products for use in electronics has rapidly increased over the years with a special focus on nanocrystalline cellulose-based nanocomposites. Cellulose is an abundant, natural polymer that possesses great strength and biodegradability, which makes it an ideal candidate as reinforcement fillers in electronics. In this study, nanocrystalline cellulose will be extracted from purified wheat straw and wood biomass via strong acid hydrolysis with sulfuric, nitric, hydrochloric, and hypochlorous acids. A comparison of the surface and structural differences of the polymer caused by the varying acids will be examined with x-ray diffraction analysis, atomic force microscopy, and scanning electron microscopy. To increase the hydrophobicity of nanocrystalline cellulose, chemical modifications consisting of acetylation, coupling reactions, esterification, Jones oxidation, Clemmensen reduction, and hyrdazone formation will be used to modify the cellulose structure. Subsequently, mechanical and thermal properties of the modified polymers will be investigated which will allow additional insight into characteristic improvements or regressions.
Acknowledgements: The authors gratefully acknowledge the National Science Foundation under Grant Nos. NSF EPS-1158862, NSF HRD-1137681, and NSF IGERT on Sustainable Electronics DGE-1144843 for support of this research.

Eco-friendly organic solar cells (OSCs) have attracted great attention according to the growth of interest in alternative to harmful materials. Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), which was one of the most commonly used material as an interfacial layer in OSCs, had adverse effect to OSCs in terms of prolonged stability and environmental problems due to its high acidity (pH ~1). As PEDOT:PSS alternatives, graphene sheets have been functionalized in a non-covalent manner with biocompatible fullerenol (C₆₀(OH)_x, F-OH) where many hydroxyl groups were introduced into fullerene. F-OH was studied in the nanomedicine field due to its strong antioxidative, radioprotective, and cytotoxic modulative properties (as well as it has semiconducting property also). F-OH adsorbs onto reduced graphene oxide (r-GO) sheet and hence acts as dispersion stabilizer preventing irreversible aggregation and can possibly be used as biocompatible material. The synthesized r-GO with F-OH (Fr-GO) showed good dispersion concentration (~2 mg/ml) in water as well as film-forming property enough to use as an interfacial layer. In addition, the structural, optical, and thermal properties of Fr-GO were characterized by XPS, FT-IR, UV-vis spectroscopy, and TGA. Finally, we will discuss the cell toxicity test of Fr-GO in vitro on mouse embryonic fibroblast cells and possibility for the utilization of the Fr-GO as an interfacial layer in OSCs.

In a Nafion membrane, protons are well known to be transported through nanochannels made by sulfonic acid groups. The nanochannels are created by phase separation with the amphiphilic character of Nafion. Therefore, the proton conductive group orientation is also important to improve proton conductivity. Our group found that the proton conductivity of the Nafion ultra thin film decreased extremely compared to that of the commercial membrane. In the thin film, sulfonic acid groups are highly oriented and isolated each other, which results in the poor conductive channel formation.
Amino acid polymers take several hierarchical structures such as α-helix or β-sheets using hydrogen bonding between the amino acids. Our research group investigates proton transport using hierarchical structures. Poly(aspartic acid) has free carboxylic acid groups at the side chains, and the protons at these groups are mobile during proton conduction. We found that poly(aspartic acid) thin film form non-periodic secondary structures and show higher proton conductivity than their bulk sample. We speculated that the proton conductivity enhancement of it results from the formation of ordered proton conductive channel by the hierarchical structures.
We polymerized D,L-aspartic acids to form polysuccinimide. Sodium polyaspartate was prepared by the hydrolysis of polysuccinimide. Fully and partially protonation poly(aspartic acid) were obtained by using ion exchange or hydrochloric acid to polyaspartate. The poly(aspartic acid) thin films were prepared by spin coating and its orientation was characterized by an infrared multiple-angle incidence resolution spectrometry (MAIRS). The proton transport properties were investigated by the impedance measurements. The proton-conduction mechanisms were investigated by in-situ IR, in-situ QCM, in-situ GI-XRD measurements and DFT calculations.

As organic electronics continue to improve, the future of technology will be required for more environmentally friendly and better integration of green technology for sustainable organic electronics. Among all organic materials for organic electronics, biomaterial and natural compound are especially environmentally friendly, can be mass produced inexpensively, and can contribute to sustainability in organic electronics. Therefore, many researchers believe that the conventional materials for use in electronic device will be replaced by more environmentally friendly and energy productive materials such as natural compounds and bio-inspired materials. In addition, natural and bio materials based organic electronic devices have the potential to be integrated to create a new class of electronic devices and to be utilized in biomedical and environmental applications.
Indigo derivatives are well known in natural compound dyes. Among various indigo species, indigo brown (Isoindigo) has been widely used in the dye industry and can be produced easily from various natural sources. Recently, isoindigo-based semiconductors have been reported high mobilities and high photovoltaic performance. These results indicate the great potential of isoindigo as semiconductor for organic devices. Therefore, we introduce isoindigo unit to make a natural compound based polymer semiconductor.
In this presentation, we will discuss on the synthesis and characterization of isoindigo based polymer semiconductor. The basic material characterizations using NMR, DSC, TGA and GPC were investigated. In addition, optical and structural properties were analyzed using optical spectroscopy tools such as UV/Vis spectroscopy and X-ray diffraction. In addition, we demonstrate isoindigo based organic electronic devices such as organic thin film transistors and organic photovoltaics.

Printing functional inks by means of roll-to-roll compatible techniques would allow a continuous, high-volume and cost effective fabrication process of large area organic optoelectronic devices. Until now, the main criteria for the use of any material or process in the organic electronic field have been solely based on the improvement of device performance. However, if the approach of organic electronics aims to be called a truly sustainable technology more attention has to be paid in the forthcoming years to the use of biodegradable materials for the fabrication of printed optoelectronic applications.
LECs represent an alternative light-emitting device with very distinct processing advantages over organic light emitting diodes: no low work-function metal is required, presents a large tolerance to thickness variations and only one active layer is needed for its operation. The working principle of LECs is based on the dynamic formation of a p-i-n light emitting junction allowed by the existence of ionic species within the active layer. In this context, a vast variety of materials of natural origin is already known for being ionic conductors or fluorescent dyes and therefore suitable for LEC fabrication. In the present work, we will investigate the suitability of water soluble natural materials as solid polymer electrolytes (PSE) and emitters in LECs. The PSE is characterized by means of impedance spectroscopy and cyclic voltammetry. Device performance is correlated to the choice of materials, ionic mobility and film morphology.

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.

The control of the outgrowth of neuronal cultured cells is of critical importance in a wide spectrum of neuroscience applications including tissue engineering scaffolds and neural electrodes. However, the study of neuron cell outgrowth on more complex topographies remains limited. Phenotype alteration of stem cells and differentiated neuronal cells cultured on traditional flat substrates that lack structural cues, emphasize the necessity to shift from 2D to 3D cell culture models. The aim of the present study was to investigate the cellular response to topographical cues both at the micro and the nanoscale. In particular, we have previously reported that the artificial surfaces obtained by direct femtosecond laser texturing of solid surfaces in reactive gas atmosphere exhibit roughness at both micro- and nano-scales that mimics the hierarchical morphology of natural surfaces [1]. Variation of the laser fluence, alters the surface morphology, while the respective patterned substrates exhibit different roughness ratios and wettabilities. Cells with nerve cell phenotype were cultured on the substrates. Results on the culture of PC12 cells showed that the morphology of microspiked surfaces alone can be used for directional cytoskeletal rearrangement and subsequent differentiation into a neuronal phenotype. Besides this, the experiments with DRG/SCG nerve cells showed a good attachment, outgrowth and network formation and depending on the substrate morphology there was a differential orientation of the cells. In particular, cells were randomly oriented on low roughness surfaces, whereas there was a trend for parallel alignment on the intermediate and high roughness substrates. Our results indicate a method to tune cell responses by proper selection of the surface free energy of the substrate and may be promising for the design of cell culture platforms with controlled differentiation environment.
[1] V. Zorba, E. Stratakis, M. Barberoglou, E. Spanakis, P. Tzanetakis, S. H. Anastasiadis and C. Fotakis, Advanced Materials 20, (2008), 4049.

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 presence of damage products with high selectivity and sensitivity. We have shown sensitive and selective electrochemical sensing of 8-oxoguanine and uracil repair glycosylase activity by electrochemical analysis with DNA monolayers on gold with silicon chips and low-cost electrospun nanofibers. Our approach compared the electrochemical signal of redox probe modified monolayers containing the defect versus the rational control of defect-free monolayers. We found sequence-specific sensitivity thresholds on the order of femtomoles of proteins and dynamic ranges of over two orders of magnitude for each target. Temperature-dependent kinetics were extracted, showing exponential signal loss with time constants of seconds. Nanofibers were shown to behave similarly to conventional gold-on-silicon devices, showing the potential of these low-cost devices for sensing applications. Thus, this device approach enables sensitive, selective, and rapid assay of repair protein activity, enabling a biological interrogation of DNA damage repair.

Organic (semi-)conductors have stepped on the bioelectronics field proving furtherance in their mechanical properties and formation of intimate interfaces with living tissue with respect to their inorganic counterparts [1]. Even though transduction of ionic biosignals to electronic signals is thought to be the key mechanism for successful integration of electronic devices in biological systems, little work has been developed in understanding the interplay of electronic and ionic conductivity of the relevant materials [2]. Here we present a materials science approach that addresses the conductivity properties by blending conjugated polymers with insulating organic materials, such as poly(vinyl alcohol) (PVA). This study has already shown improved hydrophilicity of the blend, which has a potential impact on its tissue engineering applications given the importance of cell adhesion and proliferation on these surfaces. Most importantly, electronic transport remained successful and field-effect was observed in such systems. This approach is expected to confer the resulting blend highly improved ionic conductivity, not only for the polar nature of the utilized commodity polymers, but also due to the swelling of the blend in the electrolyte (ultimately biological medium). This effect would in turn positively affect the performance of electrophysiological recordings and stimulation.
[1] R. M. Owens et al., MRS Bulletin, 35, 449 (2010).
[2] S. Ghosh et al., Electrochemical and Solid-State Letters, 3 (5), 213 (2000).

We have five senses, which are the sense of vision, sound, touch, smell, and taste. Among these five senses, the sense of smell and taste is the chemical sense, while the other three senses are physical sense. Regarding the sense of vision and sound, human developed the devices which can measure their activating stimuli, which are light and vibration. However, we do not have any device which can measure the smell and taste. We still depend on the sensory evaluation using our own nose and tongue.
The olfactory system plays an important role in recognizing environmental conditions. Since olfactory receptor genes were identified and cloned, various researches on olfactory systems have been carried out, and the interest in olfaction research has been increasing due to its potential industrial applications. In the smelling process, the binding of specific odorants to the olfactory receptor proteins is the initiation step in odor recognition and triggers signal transduction in a cell. Functional expression of the olfactory receptors on the surface of culturable cells is very useful for application to an olfactory and sensor.
“Bioelectronic nose” consists of primary and secondary transducers. The primary transducer is a biological sensing element that is human olfactory receptor, and the secondary transducer is a nanotube. The bioelectronic nose has sensitivity and selectivity comparable to the natural human nose. Moreover, it demonstrates specificity characteristics similar to those in the cellular signal transduction pathway and displays antagonistic behavior similar to the natural human nose.
This bioelectronic nose can be used in industrial applications as an extremely specific and sensitive sensor as well as in scientific applications for studying the mechanism of olfaction and the interaction between olfactory receptors and odorant molecules. It can be used for standardization of smell, smell industry, medical diagnosis, food quality assessment, environment monitoring, process monitoring, public safety and so on.
In this presentation, sensitivity, selectivity, stability and human analogy of the bioelectronic nose will be discussed, and some representative application examples will be also demonstrated.

Organic Electrochemical Transistors (OECTs) are based on a planar structure consisting of three electrodes: two of them, the source and drain, are the two terminals of a channel, while the third electrode, the gate, is separated from the channel by an electrolytic solution, which enables the ionic conduction between them. The operative regime of OECTs depends on the material used as channel and gate electrode. When the interface between the gate contact and the electrolyte is non polarizable, the OECTs operates in a faradaic regime as redox reactions occurs at their interface. On the contrary, when the metal-gate has polarizable interface, the OECTs operates in a capacitive regime there is no charge transfer at its surface; in this case, the performance of the device depends on the gate geometry. OECTs which have both the channel and the gate contact made of PEDOT:PSS have a pseudo-capacitive behavior, already demonstrated in [1]: in the whole working range of the transistor the device behaves in a pseudo-capacitive regime because both electrodes (gate and channel) are able to exchange charge by means of a faradaic process, and at the same time to charge and discharge the electrical double-layer at the interface with the electrolyte. In the present work, this investigation has been extended, considering solutions containing a mediator (Ferrocene) able to undergo a faradaic reaction in the voltage range of the transistor operation. In addition, the device has been operated in solutions containing Ferrocene, Glucose Oxidase (GOx) and different concentrations of glucose, in order to probe the device ability to work as a glucose sensor. Finally, we will present data obtained with devices fabricated with Ferrocene-clicked PEDOT:PSS coated by GOx in order to allow the employment of such sensors for biological samples with no need of sample preparation.
[1] M. Demelas, R. Rogani, E. Scavetta, A. Bonfiglio, APL, 102, 193301, 2013

The ultimate goal for biodiagnostics is to provide a minimally invasive technology that combines rapid analysis and low cost fabrication. Label-free detection is an added advantage that decreases assay cost and operator time. One promising new technology that has the potential to respond to these specific requirements is the organic electrochemical transistor (OECT). We take advantage of the operating principle of the OECT to fabricate a sensor capable of detecting low concentrations of a variety of physiologically relevant metabolites. During redox cycles, the metabolic analyte (glucose or lactate) and its corresponding enzyme (glucose oxidase or lactate oxidase) react, resulting in the transfer of an electron through a mediator (hydrogen peroxide) to the gate electrode. The electronic modification of the gate electrode induces a change in the transistor drain current that is proportional to analyte concentration. Incorporation of the biorecognition element directly into the device via functionalization can result in a one-step sensing platform. In this work, we incorporate functionalization sites within the conducting polymer (CP) PEDOT:PSS {poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate)} films by adding polymers with reactive sites while at the same time retaining conductive properties of the CP. Subsequently we fabricate planar OECTs with this functional conducting polymer serving as the transistor channel and gate. Enzymes are then cross-linked within the transistor. Additionally, we incorporate Pt nanoparticles to enhance the electron transfer. We demonstrate highly sensitive analyte detection using these functionalized OECTs. The resulting device is capable of continuous, longterm measurement. Due to the inherent advantages of conducting polymers and the robust functionalization demonstrated, the described sensing platform represents a significant step towards the realization of low-cost electronic-based sensors for metabolite detection.

Human-device interface can be augmented by the breakthroughs of the key technological venues in miniaturized, energy efficient and biocompatible sensors, actuators, and batteries. Graphene has been recognized as an excellent material for creating flexible sensors due to their unparalleled electronic, optical, and mechanical performance. Amino acids or nucleic acids in the form of short or long chains offer exquisite sensitivity and selectivity towards analytes. Nanosized graphene can primarily serve as a transducer that converts the molecular level binding activity of the chemical/biological molecules into an electronic output signal. In this presentation, we will describe our efforts in developing designer biomolecules that interact with graphene nanomaterials, and their uses in flexible sensor platforms. We will specifically focus on the understanding of biomolecular conformation on graphene surfaces, and binding kinetics and ultimately sensing performance.
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Large amplification and fast response are essential for transistors in applications ranging from switching elements to measurement of fast biological events such as neuronal action potentials. To this end, organic electrochemical transistors (OECTs) based on conducting polymers such as PEDOT:PSS {poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate)} have been recently targeted for applications in environmental and biological sensing due to their efficient ionic to electronic signal transduction in aqueous. OECT operation relies on the modulation of drain current by the de-doping of PEDOT upon application of a gate bias (which causes a drift of cations into the bulk of the channel). Through active material structure-property investigations as well as micron-scale fabrication and optimization we present a solution processed micron-scale OECT with a transconductance approaching 4 mS. Optimization of geometry reveals the limiting mechanisms for device switching - a competition between ionic drift into the channel or hole transport from source to drain. With proper device design, PEDOT-based OECTs can be made to completely shut off (with 10-70 mV/decade sub-threshold slopes and on:off current ratios exceeding 10⁵) and to exhibit peak transconductance without an external gate-bias, limiting unnecessary voltage application to the biological system and simplifying probe design. The relative ease of fabrication and ability to embed active devices in thin polymeric substrates allows for extreme flexibility, maintaining high performance after aggressive crumpling. Along with stable operation in vivo and in cell culture, such characteristics make OECTs ideal candidates for low signal, transient biological recordings.

Integrating functional biological elements in electronic devices is a research topic that has been stimulating scientific studies since the seminal work by Fromherz [1]. Relevant applications in field-effect type biosensors can be traced back to the work of Bergveld [2]. These efforts involved inorganic-type transistors and more recently organic electronic devices have been coupled to receptors, neurons and even tissues [3].
This invited presentation will focus on the integration of Functional Biological Interlayers (FBIs) into Organic Field-Effect Transistors (OFETs) [4]. With the intent of studying the interface between an FBI and the organic semiconductor electronic channel, a set of proteins with well assessed biological properties have been selected. Specifically streptavidin, avidin and neutravidin are integrated and the impact of their interaction with biotin on the OFET electronic channel will be reported. Particular regard will be given to effort of decoupling biological complex formation contributions affecting the threshold voltage shift from those affecting field-effect mobility changes. The challenges and the issues connected with this activity will be highlighted.
[1] P. Fromherz, in Nanoelectronics and Information Technology, R. Waser, Ed. (Wiley-VCH Verlag, Berlin, 2003), pp. 781-810.
[2] P. Bergveld, Sens. and Actuat. B, 88(1), 1-20 (2003).
[3] L.H. Jimison, S.A. Tria, D. Khodagholy, M. Gurfinkel, E. Lanzarini, A. Hama, G. G. Malliaras and R. M. Owens, Adv. Mater. 2012, 24, 5919-5923
[4] D. Angione et al. PNAS, 109(17) 6429-6434 (2012).

Organic electrochemical transistors (OECTs) have been investigated in the last decade as sensors for hydrogen peroxide, glucose, dopamine, chloride ions, cells and bacteria as well as devices to control cell adhesion. However, despite these important studies, the working mechanism of OECTs remains largely undiscovered.
Currently, most OECTs are based on the conducting polymer conducting polymer poly 3,4 ethylenedioxithiophene doped with polystyrenesulfonate (PEDOT:PSS). PEDOT:PSS films for OECTs are obtained from aqueous suspensions (Clevios PH1000), which need to be mixed with an organic compound (secondary dopant) to increase film conductivity. Upon application of a negative drain-source bias, a hole current (source-drain current) flows into the OECT channel. The application of a positive gate bias induces a reversible redistribution of positive ions within the film and the electrolyte. This, together with charge injection from source and drain, results in electrochemical dedoping of the transistor PEDOT:PSS channel, accompanied by a decrease of the source-drain current, whose extent depends upon the applied gate bias.
Although the role of secondary dopants is still under debate, it has been ascertained that their presence is required to achieve high conductivity. Typically employed secondary dopants are ethylene glycol, dimethyl sulfoxide, sorbitol and glycerol. To date, it is still unclear which one of these dopants is best suited for OECTs. In our experiments (with films deposited by spin-coating) we investigated various formulations, with the aim to elucidate the correlation between the conductivity and the effectiveness of the doping/dedoping process. Our results open new perspective for the use of OECTs in sensing and bioelectronics devices.

Aqueous dispersions of reduced Graphene Oxide (rGO) and multi walled carbon nanotubes (MWCNT) were fabricated through a modified chemical reduction method. The significant advantage of the method developed here is the omission of any stabilizing compound or organic solvent to obtain stable rGO-MWCNT dispersions. Significantly biological entities, in this case the enzyme glucose oxidase (GOx), can be successfully incorporated into the dispersion. These dispersions were characterised using XPS, SEM, zeta potential and particle size measurements which showed that the dispersion stability is not sacrificed with the addition of GOx, and significantly, the electrical properties of the rGO and MWCNTs are maintained. In this study, rGO acts as an effective dispersing agent for MWCNTs and does not affect the solubility or electroactivity of the GOx.
Bioelectrodes fabricated from these rGO-MWCNT-GOx dispersions were characterised electrochemically to test their feasibility in facilitating direct electron transfer (DET) from the redox centre of the enzyme to the electrode. The DET results showed that the specific catalytic current generated at an optimized rGO-MWCNT-GOx electrode was 72 mu;A/mu;g GOx, which is 144 times more efficient than other literature values for similar systems. The remarkable specific catalytic current can be attributed to the use of purified enzyme, the efficiency of charge transfer within the rGO-MWCNT composite and the ability of the electrode to facilitate direct electron transfer.

The ubiquitous natural pigment 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 ionic-electronic conduction in a hydrated state [1,2]. To further explore the use of eumelanin in organic bioelectronic devices, the properties of eumelanin thin films interfaced with device components such as metal electrodes need to be investigated in presence of water and ionic species. A good understanding of the interaction of eumelanin with different metal electrodes is also essential to study the intrinsic charge transport properties of eumelanin films, which are still largely undiscovered.
We characterized eumelanin films grown on substrates patterned with gold, platinum, and palladium hydride electrodes using hydration-dependent transient electrical current and atomic force microscopy measurements. We discovered an electrochemical interaction among metal-chelating catechol groups of hydrated eumelanin, Cl- traces in the eumelanin material, and Au electrodes, assumed to be electrochemically stable in previously published works on the electrical properties of eumelanin. This interaction leads to the growth of highly conductive Au-eumelanin dendrites between the electrodes, ultimately leading to sudden resistive changes of the sample. This phenomenon suggests new possibilities for biocompatible memory devices and has to be taken into account when integrating eumelanin-like materials in electronic devices [3].
Electrical characterization of eumelanin films interfaced with ion-blocking Pt and proton-transparent PdHx electrodes complemented by Kelvin probe force microscopy and impedance spectroscopy measurements gave new insights into the charge transport properties of eumelanin films. Our results indicate the presence of electronic and protonic currents in eumelanin thin films, both increasing with sample hydration. These results support recently published data obtained by spectroscopic measurements on eumelanin pellets [2] and underline the attractiveness of eumelanin films for applications at the interface of electronics and biology.

[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. Wünsche et al., Adv. Funct. Mater., DOI:10.1002/adfm.201300715 (2013)

Conducting polymers (CPs) attract an increasing attention for a wide range of biomedical applications including implantable electronics, biosensing, drug delivery, and tissue engineering. These organic polymers are easy to process, and their physical properties such as volume, color, wettability, and conductivity can be precisely tailored to the particular application. Among those polymers, biocompatible nature of polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT) has positioned them as the most commonly applied CPs in biological studies. Films of PPy and PEDOT can be synthesized by electrodeposition. During electropolymerization, biomolecules, such as nucleic acids, enzymes, and antibodies, can be incorporated into the polymer film as dopants or physically entrapped while retaining their activities. This provides a convinient way to immobilize bioactive molecules on these polymer films, and when patterned, such films offer appealing platforms for sensing applications as well as studies of cell attachment, proliferation, and differentiation.
In this work, we report an innovative and simple approach for selective and direct deposition of PPy and PEDOT films with entrapped biomolecules in a single-step process using hydrogel stamping. In this approach, a patterned agarose stamp loaded with monomer and desired dopant (e.g. poly(styrenesulfonate) (PSS)) is placed on a conductive substrate. The stamp delivers these molecules onto the electrode surface, and upon application of a voltage, a film of doped CP is deposited on the substrate in areas of contact between the gel and substrate. The applied agarose stamps are also well-suited for the storage and delivery of fragile biomolecules. Hence, the agarose stamps allow inclusion of desired biomolecules in the electrodeposited polymer network and enable multiple transfers from a once-loaded stamp. Here, we used this simple technique to create positive patterns of PPy films with different geometries and dimensions (ranging between 40 µm and 1 mm). Resultant patterned films were characterized using optical microscopy, scanning electron microscopy, and impedance spectroscopy. We investigated the effect of monomer concentration, hydrogel agarose content, electrodeposition time, and current density on the synthesis of polymer films. By loading biomolecules in agarose stamps along with monomer and dopant, we generated patterned PPy films decorated with bioactive molecules. Moreover, we examined the capability of agarose stamps to simultaneously deposit CP films with different dopants tuning their properties. Finally, we explored the potential of this method to directly create CP films with gradients of dopants and biomolecules. In summary, the present approach enables direct deposition of CP films decorated with desired biomolecules in a single-step and solution-free method. The resultant patterned films will next be applied for biosensing and tissue engineering.

Electrospun nanofibers can be readily produced with tunable and well-controlled compositions, diameters, porosities, and porous structures for a variety of applications. Owing to the small feature size, high porosity, and large surface area, a nonwoven mat of electrospun fibers can serve as an ideal scaffold to mimic the extra cellular matrix (ECM) for cell attachment and nutrient transportation. The fibers themselves can also be functionalized through encapsulation or attachment of bioactive species such as ECM proteins, enzymes, and growth factors. the fibers can be further assembled into a variety of arrays or hierarchical structures by manipulating their alignment, stacking, or folding. Furthermore, the surfaces of nanofibers can be easily coated with conductive polymers to allow for the application of electrical field. All these attributes make electrospinning a powerful tool for generating nanostructured materials for a broad range of biomedical applications that include controlled release, drug delivery, and nerve tissue engineering. In this talk, I will discuss how the conventional setup for electrospinning can be modified to control the composition, structure and alignment of nanofibers. Specifically, I will focus on the use of aligned nanofibers to control the differentiation of embryonic stem cells into different types of neural lineages and to guide the outgrowth of neurites for peripheral nerve repair. I will also discuss how nanofiber scaffolds can be designed for nerve tissue engineering, injury repair at the insertion site between tendon and bone, and as substitutes for dura mater in brain surgery.

Attempts to interface human-made systems with neural systems are commonly based on direct electrical stimulation or exogenous drug delivery. Few techniques have attempted to mimic the neuron&’s combination of electronic and chemical signaling with endogenous substances. To address this issue, our research group has developed the organic electronic ion pump (OEIP), a conducting-polymer and polyelectrolyte-based technology capable of neuron-like transduction of electrical signals into controlled delivery of ions, neurotransmitters and other bio-substances. Based on electrophoretic migration through an organic electronic system, delivery is diffusive and non-convective, and thus doesn&’t disrupt fragile biochemical microenvironments. We have demonstrated the OEIP both in vitro and in vivo, and have also developed the technology into diodes and transistors for ionic logic (rather than the traditional electronic). Recently, we have combined OEIP delivery with amperometric biosensors to create a delivery system regulated by the local concentration of bio-active substances. The system mimics the function of a biological neuron: chemical sensing at the synapse, leading to electrical signal transduction (action potential), and eventually chemical delivery (synaptic release). Parallel research efforts have led to the OEIP&’s incorporation into microfluidic delivery systems for precise generation of molecular cocktails for treatment of spinal injuries. This system represents a first step in the iONE-FP7 research effort to incorporate a variety of organic electronic technologies into a fully integrated, biodegradable spinal injury therapeutic implant. In this presentation, we will discuss the OEIP itself, its application in a variety of in vitro and in vivo settings, and its current state of development. We will also focus on the role for ion- and molecule-based “iontronics” in biological applications, and their advantages for new diagnostics and therapies.

Microelectrode arrays (MEAs) have become an indispensable tool in the study of different neuronal network properties in vitro. The traditional technology is based on micro-sized metallic electrodes produced through photolithographic etching of physically deposited noble metal coatings. As the size of the electrodes decrease, however, both signal quality and stimulation ability drop due to the high impedance of the metal-tissue interface. Conducting polymers such as poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS), show lower impedance and higher capacitance compared to metals, as well as an augmented biocompatibility. Here, we present a novel approach to photolithographically define polymer MEAs, which are capable of recording spontaneous unit activities from mouse hippocampal slices. MEAs still require local electronic amplifiers in order to maintain the desirable signal-to-noise ratio. As opposed to simple electrodes, organic electrochemical transistors (OECTs) are active devices employing conducting polymers capable of transducing small ionic fluctuations into measurable electronic currents. Recent advances on the use of these devices for single unit electrophysiological recording will be discussed.

Resistors, diodes and transistors for ionic signals based on polyelectrolytes have been developed. In these organic iontronic devices electronic addressing signals are translated into processing and delivery of ionic signals, such as cations and neurotransmitters. We have explored analogue and digital iontronic circuits aiming at precisely regulating functions and physiology in living cell systems, in vitro and in vivo.
Here, we report iontronic devices and circuits that operates at high spatiotemporal resolution and at high speed that have been applied to various eukaryotic cell systems. For instance, iontronic circuits have been explored to regulate sensory functions and signalling in the spinal cord and in the cochlea of different mammalian model systems. The iontronic “chemical chip” technology may blaze the trail for new prosthesis and therapy methods in biology and medicine.

To better understand the human body and brain, it is necessary to develop new approaches to track neural interactions in the central and peripheral nervous systems. Towards this end, sophisticated neural devices can be fabricated with high levels of complexity using photolithography on flexible substrates compatible with organic thin film transistors (OTFTs). We explore how to integrate functionalized stimulation electrodes in a matrix array on photolithography compatible, flexible, physiologically responsive, biocompatible substrates that can withstand the environment of the body while softening to decrease the mechanical mismatch with the body tissue. This softening substrate reduces scar tissue formation around devices enabling more intimate neural contact. To accomplish a desirable interface for charge injection in between the electronics and the neurons, we functionalize electrodes using fractal nanostructured TiN and IrO, The nanostructure of the electrode materials gives a high ratio of electrochemical surface area (ESA) to geometric surface area. These materials are well known for high charge injection capacity (CIC) and chemical stability. Reliable electronics in the neural interface are sought through integration of OTFTs using the air-stable semiconductor dinaphtho [2, 3-b: 2prime;, 3prime;-f] thieno [3, 2-b] thiophene (DNTT): resulting transistors have mobilities up to 0.5 cm2/Vs and threshold voltages close to 0V. Devices are measured in air and in PBS to simulate in vivo conditions, as fabricated and over different time scales. To enable viable chronic behavior in vivo, the OTFTs are encapsulated with softening smart polymer barrier layers alone or in conjunction with inorganic layers such as HfO2.Transistor characterization as well as impedance and CV curve measurements for the functionalized electrodes are performed. These devices enable the development of new applications with added circuit complexity to make possible a host of biomedical sensing and stimulating devices. This study will help us understand the impact of using OTFTs in vivo and the fundamental problems for biocompatible, long-term electronic devices implants, leading to a new set of tools and devices that will help address grand challenges in neuroscience and electrophysiology.

We continue to be interested in the development of conjugated organic polymers and copolymers for interfacing a variety of hard, inorganic metallic and semiconductor, engineered biomedical devices with ionically-conducting, soft, living neural and muscular tissue. Recently we have been designing, synthesizing, and characterizing the properties of chemically-functionalized versions of the 3,4-ethylenedioxythiophene (EDOT) and 3,4-propylenedioxythiophene (ProDOT) monomers. Examples include carboxylic-acid functionalized EDOT (EDOT-acid), and thiol-ene functionalized ProDOT. We are also investigating branched variants of both EDOT and ProDOT to improve mechanical properties through crosslinking. These new monomers require variations in the electrochemical deposition conditions, including alternative choices for solvents and counter-ions. We have characterized the resulting PEDOT and P(ProDOT) polymers and copolymers using a variety of techniques including optical and electron microscopy, X-ray diffraction, electrochemical impedance spectroscopy, and biological activity assays. These materials make it possible for us to systematically tailor the stiffness and toughness of the films, their adhesion to solid substrates, their charge transport properties, their wetting behavior, and their specific interactions with cells.

Molecular recognition of biomaterials is prevalent in nature and plays a key role in several important biological interactions such as pairing of complementary DNA sequences and binding of antibody and antigen. Such molecular recognition can also be extended to non-biological materials. For example, various peptides with binding affinity toward graphitic surface have been explored to functionalize single-walled carbon nanotubes and graphene to add functionalities to those nanocarbon materials without deteriorating their excellent electrical properties. In the previous works, however, peptides were mostly utilized to either stabilize nanocarbon materials in aqueous solutions or functionalize solid substrates coated with nanocarbon materials, and therefore their utilization to electronics application has been limited. Here we exploit molecular recognition between peptides and nanocarbon materials to fabricate high performance graphene/single-walled carbon nanotube hybrid films without chemical modification of those nanocarbon materials, potentially being useful for electronics applications. To make a free standing hybrid film, surfactant-dispersed graphene sheets and single-walled carbon nanotubes are incubated with M13 phage with its p8 peptides having strong binding affinity toward graphitic surfaces and dialyzed. The resultant hybrid films have several important characteristics. First, it can be ultrathin (~ 45 nm), in large scale (> 3 cm) but is naturally free-standing. Therefore it is transferrable onto any substrates without harmful chemical etching, ensuring benign and flexible materials fabrication. Second, the hybrid film is very conducting and presents a high effective surface area due to its percolating network structure. When a 45 nm-thick film is transferred onto a Pt surface, capacitive current density increases by more than 11 times compared with bare Pt surface, and the current density is higher than Pt by more than 3 times even when transferred onto insulating substrates, implying its excellent electrical properties. Third, the film is hydrophilic due to the embedded M13 phage and additional biological functionality can be easily incorporated into the film using functional groups of the phage. We believe that our bio-inspired hybrid materials platform presents a new approach to utilization of nanocarbon materials and can be very useful for various applications including bio-interfacing organic electronics, sensors and stimulators.

There has been significant and ongoing interest in devising systems that self-assemble into higher order nano- or meso-structures. The self-assembly of amphiphilic molecules into discrete organized assemblies is not only fundamentally interesting, but provides a facile means by which to produce functional materials for energy storage and transduction. The exploitation of ionic liquid structural modularity coupled with chemical modification of the cation or anion is now an active area of research resulting in the development of ionic liquid-based materials. Chemical moieties can also be added to allow for capture of the self-assembled architectures in a durable form by polymerization and / or crosslinking, rendering the materials environmentally stable and mechanically durable. The current focus of our research is the preparation of ionic electroactive polymers for use as biocompatible materials for charge / electronic management between conventional materials (metal and semiconductor electrodes) and proteins. Specifically, two polymeric ILs that achieve direct electronic communication to recessed protein prosthetic groups and function as bulk electronic conductors will be presented. The first material is an Au-nanoparticle-poly(ionogel) composite that contains surface-exposed nanoparticles for facilitated direct electronic communication to buried redox centers of a protein. The second material is an electronically conductive pi-conjugated poly(ionogel) that contains a unique reactive moiety for site-specific electronic wiring to a protein. Ultimately, the ionic electroactive poly(IL)s will serve as a platform for the fabrication of a wide range of bioelectronic devices, including the construction of biofuel cells and photovoltaics.
This work was performed under the auspices of the Office of Basic Energy Sciences, Division of Materials Sciences, United States Department of Energy, under contract No. DE-AC02-06CH1135.

Edible electronics serves as an attractive format to deploy electronically active medical devices for functions such as sensing and stimulation of tissues. Oral delivery of electronics ensures that devices can be deployed in the body temporarily and in a non-invasive manner. There are many materials challenges that need to be addressed in order to realize the therapeutic potential of edible electronics. Here, we will highlight recent efforts in our laboratory at overcoming two particular hurdles: (1) supplying power to edible electronics and (2) designing ultra-compliant electrode materials that are suitable for improving tissue-device interfaces. In the first thrust, recent work on bio-inspired materials for sodium ion storage devices will be discussed. The second part of the presentation will focus on recent progress in hydrogel-based electrodes. Taken together, the advances in materials will provide a solid foundation for future advances in edible electronics.

The electric transport properties of organic materials have attracted much attention because of their potential applications in electronic and optoelectronic devices. Natural polymers, such as chitosan, have been studied as alternatives for inorganic materials due to their properties such as biodegradability, biocompatibility and non-toxicity, which allows applications in medicine, food engineering, materials science and or the development of biosensors and fuel cells, serving as matrix for enzyme immobilization. However, the acidity of chitosan films can affect the activity of bioreceptors, and therefore, prior to immobilization of enzymes, a neutralization step is required to prevent the loss of enzymatic activity or its denaturation. Salts additions can be used to increase pH in the precursor solutions of films. However, these salts dissociate in their ions affecting the electrical conductivity of these materials. Transport can be strongly affected by three different levels of disorder: disorder present in the global structure influenced by topology matrix, the interparticle coupling and the random distribution of charges. The aim of this work is to explore the effect of different salts on electrical transport of chitosan films. Chitosan solutions, neutralized with NaOH or KOH to increase the pH from 4.3 to 6.0, were used to produce the films by casting technique. Chitosan films without neutralization were also produced as control samples. The presence of ions in chitosan films from salts used for neutralization affects the electrical properties of the films leading to an increase in the current when compared with chitosan films without neutralization and the appearance of hysteresis in the current-voltage (I-V) curves, which is not perceived in the control sample. This behavior can be attributed to ion mobility in the polymeric matrix, where ions can move through the chitosan chains in presence of an applied voltage. These chains can act as traps for accumulation of ions, resulting in a space charge distribution within the polymer. By analyzing the density of states (DOS) function obtained from the experimental current-voltage curves, the effects of salt can be associated to trap states.

Implantable bionic devices interact with electrically active living cells such as nerve and muscle cells through translation of biological signals to electrical signals at the electrode-tissue interface. In these devices, long-term functionality of the biotic-abiotic interface is vital. While existing electrodes are fabricated from biocompatible metallic materials; the hard, dry, static nature of these metals is quite foreign to biological tissue. Therefore, the quality of recording and stimulating signals often deteriorates, probably owing to the process of electrode encapsulation by fibrous tissue and cell death in the vicinity of the electrode. Conducting polymers (CPs) are attractive alternatives to conventional electronic materials for biomedical application due to the following characteristics: (1) their organic nature, (2) their dynamic behavior (volume, color, and wettability changes), (3) their ability to be decorated with biomolecules, and 4) their ionic and electronic conductivity. While CPs have mechanical properties more similar to biological soft tissue than metals do, these materials are still not as soft and flexible as most native tissues, limiting their biomedical applications. The incorporation of softer polymeric materials such as hydrogels with the CPs may lead to a material ideal for soft electronics and interfacing with biological systems.
The goal of this study was to fabricate electrode-free soft conductive nanofibers. Due to their low processability, CPs cannot be fabricated into nanostructures without using a hard templating method. Here, we present a novel fabrication method with fewer steps including the electrospinning of poly(ethylene oxide) (PEO) solutions with 0 to 25 wt% of conducting polymer poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) nanoparticles. Nanofiber morphologies and diameters were characterized using scanning electron microscopy. The diameter of conductive hydrogel nanofibers ranged between 220nm to 435 nm. Energy-dispersive X-ray spectroscopy was performed on nanofibers to confirm successful incorporation of PEDOT:PSS during electrospinning. We used impedance spectroscopy and cyclic voltammetry to characterize the electrical performance of conductive hydrogel nanofibers. The inclusion of higher amounts of PEDOT:PSS decreased the impedance of the substrates. The addition of the PEDOT:PSS nanoparticles into hydrogel nanofibers decreased the swelling ratio of the material from 50 for plain PEO nanofibers (0 wt% PEDOT:PSS) to approximately 40 for those containing the nanoparticles (25 wt% PEDOT:PSS). Tensile mechanical tests were conducted on a mechanical tester with a 10N load cell. The average Young&’s modulus reduced from 14 ± 1.6 kPa to 4.3 ± 0.5 kPa as the percentage of PEDOT:PSS increased from 0 to 25 wt%. Future applications may range from electrically controlled drug delivery, neural tissue engineering, and flexible electronics.

Biomaterials offer opportunities for devices that operate at the interface of the biological and technological worlds. Stringent requirements on material form and function are imposed when operating at the nanoscale or when interfacing such materials with microelectronic circuitry. In this talk we will present recent progress on the use of silk fibroin as the material base for nanostructured optical materials and thin-film electronics. Devices such as silk-based photonic crystals, lasers, wireless antennas and resorbable electronic will be described as some examples of the possibilities that this water-processed, biocompatible material offers.

Despite the ubiquity of proton transfer in biological systems, solid-state proton conductors from naturally occurring proteins have proven vastly inferior to their artificial, man-made counterparts. We have discovered unexpected bulk proton conductivity in thin films from a naturally occurring structural protein. In the solid state, this protein features conductivities as high as 2.6 x 10^-3 S/cm, with a proton transport activation energy of 0.21 eV and a proton mobility of 4.1 x 10^-3 cm² V^-1 s^-1, thereby enabling the fabrication of protein-based protonic transistors. Such figures of merit indicate that our unusual structural protein essentially displays the electrical behavior of a dilute acid. Our findings hold important general implications across the fields of structural coloration, renewable energy, and biological electronics.

Natural-origin materials have recently found increasing applicability in the field of organic electronics. Here we present the use of cellophane, a regenerated cellulose polymeric material, in organic electronics. It is 100% biodegradable and it is most commonly used for food wrapping, adhesive tapes and semi-permeable membranes. Cellophane can be fabricated into thin, flexible and optically transparent substrates for organic electronics. We investigate polymer solar cells fabricated directly on cellophane substrates using normal and inverted structures. Cellophane is also suitable as a substrate material for organic field-effect transistors. Cellulose acetate, which can be processed from organic solvents, can be used as a gate dielectric material. These results show that cellulose can be engaged successfully into “green” organic electronic devices.

OLED displays are starting to be incorporated into an increasing number of electronic devices, from smartphones to TV sets. The main immediate advantage of OLEDs is the brilliant colors that they produce. For mid-term future generations, important considerations include improving fabrication yield, reducing cost, implementing non-planar and flexible device technology.
We review the incorporation of natural biomaterials in OLEDs to achieve some of these goals. The first aspect is the use of natural DNA to achieve specific electronic function within the OLED device structure [1]. We have used natural DNA from salmon sperm, which is a relatively low cost biomaterial derived from the salmon industry where it is normally considered a waste by-product. DNA-surfactant films exhibit excellent electron-blocking HOMO/LUMO levels that make it ideal in OLED device and other optoelectronic devices [2]. DNA-based BiOLEDs were first shown to be successful with fluorescent (Alq3) emission OLEDs. [3] More recently, we have also incorporated DNA into phosphorescent (Ir-complex) OLEDs, which utilize all possible electron recombination states and have potential for 100% internal quantum efficiency. Using DNA-surfactant thin films as electron blocker layers in green-emitting phosphorescent BiOLEDs resulted [4] in outstanding performance in brightness (up to ~ 100,000 cd/m2) and current efficiency (up to ~ 89cd/A), much superior to baseline devices without DNA. Similar increases in performance for DNA-based OLEDs was shown for red and blue emitting Ir-based phosphorescent OLEDs. Most importantly, the DNA-OLEDs for all three colors exhibit maximum efficiency for brightness in the range of ~100-300cd/m2, making it an ideal candidate for efficient display technology.
The second aspect of natural biomaterial incorporation in OLEDs to be discussed involves the use of cellulose (the most abundant biopolymer on earth) as a paper substrate. There is increasing interest [5] in using paper and associated high throughput and low unit cost printing technology for the fabrication of future electronic devices which combine very low cost, large format, flexible characteristics. OLEDs fabricated on both opaque and transparent paper substrates will be discussed.
[1] A. J. Steckl, Nature Photonics, 1, 3 Jan. 2007.
[2] Z. Yu, J. A. Hagen, Y. Zhou, D. Klotzkin, J. G. Grote and A. J. Steckl, Applied Optics, 46, 1507, March 2007.
[3] J. A. Hagen, W. Li and A. J. Steckl, J. G. Grote, Applied Physics Letters. 88 171109, Apr. 2006.
[4] A. J. Steckl, H. Spaeth, E. Gomez, H. You and J. Grote, Optics and Photonics News, 22, 35, July 2011.
[5] A. J. Steckl, IEEE Spectrum, 48, Feb. 2013.