Mixing Insulating Commodity Polymers with Semiconducting n-type Polymers Enables High-Performance Electrochemical Transistors

Diluting organic semiconductors with a host insulating polymer is used to increase the electronic mobility in organic electronic devices, such as thin film transistors, while considerably reducing material costs. In contrast to organic electronics, bioelectronic devices such as the organic electrochemical transistor (OECT) rely on both electronic and ionic mobility for efficient operation, making it challenging to integrate hydrophobic polymers as the predominant blend component. This work shows that diluting the n-type conjugated polymer p(N-T) with high molecular weight polystyrene (10 KDa) leads to OECTs with over three times better mobility-volumetric capacitance product (µC*) with respect to the pristine p(N-T) (from 4.3 to 13.4 F V-1 cm-1 s-1 ) while drastically decreasing the amount of conjugated polymer (six times less). This improvement in µC* is due to a dramatic increase in electronic mobility by two orders of magnitude, from 0.059 to 1.3 cm2 V-1 s-1 for p(N-T):Polystyrene 10 KDa 1:6. Moreover, devices made with this polymer blend show better stability, retaining 77% of the initial drain current after 60 minutes operation in contrast to 12% for pristine p(N-T). These results open a new generation of low-cost organic mixed ionic-electronic conductors where the bulk of the film is made by a commodity polymer.

Fabrication of highly stretchable salt and solvent blended PEDOT:PSS/PVA free-standing films: non-linear to linear electrical conduction response

Nowadays, ductile and conducting polymeric materials are highly utilizable in the realm of stretchable organic electronics. Here, mechanically ductile and electrically conducting free-standing films are fabricated by blending different solvents such as dimethyl sulfoxide (DMSO), diethylene glycol (DEG) and N,N-dimethylformamide (DMF), and salts such as silver nitrate (AgNO3), zinc chloride (ZnCl2), copper chloride (CuCl2) and indium chloride (InCl3) with the homogeneous solution of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and poly(vinyl alcohol) (PVA) through solution casting method. The presence of salt modifies the PEDOT conformation from benzoid to quinoid, and induces the evolution of different morphologies. ZnCl2 or AgNO3 blended films have lower surface roughness and good miscibility with polymers, while CuCl2 or InCl3 blended films have relatively higher surface roughness as well as irregularly distributed surface morphology. Some crystalline domains are also formed due to the salt agglomeration. The presence of salt inside PEDOT:PSS/PVA/solvent system changes the current-voltage response from non-linear to linear. Among all the films, zinc salt blended PEDOT:PSS/PVA/DMSO, PEDOT:PSS/PVA/DEG and PEDOT:PSS/PVA/DMF films have higher conductivity, and zinc salt blended PEDOT:PSS/PVA/DEG film shows the highest conductivity of 0.041 ± 0.0014 S cm-1, while silver salt blended PEDOT:PSS/PVA/DMSO, PEDOT:PSS/PVA/DEG and PEDOT:PSS/PVA/DMF films have higher elongation at break, and silver salt blended PEDOT:PSS/PVA/DMSO film shows the highest elongation at break of 670 ± 31%. Both the charge carriers, i.e., electrons and ions, contribute to the electrical conduction, and the presence of hydrogen bonds and ionic interactions among PEDOT+, PSS-, PVA, residual solvent, salt cations and anions modifies the film behaviours. Among all the films, ZnCl2 blended PEDOT:PSS/PVA/DMSO film offers relatively superior behaviours having higher conductivity (0.025 ± 0.0013 S cm-1) and elongation at break (517 ± 15%), and therefore can have potential applications in the fields of wearable devices, bioelectronics, etc.

Surface Functionalization with (3-Glycidyloxypropyl)trimethoxysilane (GOPS) as an Alternative to Blending for Enhancing the Aqueous Stability and Electronic Performance of PEDOT:PSS Thin Films

Organic mixed ionic-electronic conductors, such as poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), are essential materials for the fabrication of bioelectronic devices due to their unique ability to couple and transport ionic and electronic charges. The growing interest in bioelectronic devices has led to the development of organic electrochemical transistors (OECTs) that can operate in aqueous solutions and transduce ionic signals of biological origin into measurable electronic signals. A common challenge with OECTs is maintaining the stability and performance of the PEDOT:PSS films operating under aqueous conditions. Although the conventional approach of blending the PEDOT:PSS dispersions with a cross-linker such as (3-glycidyloxypropyl)trimethoxysilane (GOPS) helps to ensure strong adhesion of the films to device substrates, it also impacts the morphology and thus electrical properties of the PEDOT:PSS films, which leads to a significant reduction in the performance of OECTs. In this study, we instead functionalize only the surface of the device substrates with GOPS to introduce a silane monolayer before spin-coating the PEDOT:PSS dispersion on the substrate. In all cases, having a GOPS monolayer instead of a blend leads to increased electronic performance metrics, such as three times higher electronic conductivity, volumetric capacitance, and mobility-capacitance product [μC*] value in OECT devices, ultimately leading to a record value of 406 ± 39 F cm-1 V-1 s-1 for amorphous PEDOT:PSS. This increased performance does not come at the expense of operational stability, as both the blend and surface functionalization show similar performance when subjected to pulsed gate bias stress, long-term electrochemical cycling tests, and aging over 150 days. Overall, this study establishes a novel approach to using GOPS as a surface monolayer instead of a blended cross-linker, for achieving high-performance organic mixed ionic-electronic conductors that are stable in water for bioelectronics.

Advancements in tailoring PEDOT: PSS properties for bioelectronic applications: A comprehensive review

In the field of bioelectronics, the demand for biocompatible, stable, and electroactive materials for functional biological interfaces, sensors, and stimulators, is drastically increasing. Conductive polymers (CPs) are synthetic materials, which are gaining increasing interest mainly due to their outstanding electrical, chemical, mechanical, and optical properties. Since its discovery in the late 1980s, the CP Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) has become extremely attractive, being considered as one of the most capable organic electrode materials for several bioelectronic applications in the field of tissue engineering and regenerative medicine. Main examples refer to thin, flexible films, electrodes, hydrogels, scaffolds, and biosensors. Within this context, the authors contend that PEDOT:PSS properties should be customized to encompass: i) biocompatibility, ii) conductivity, iii) stability in wet environment, iv) adhesion to the substrate, and, when necessary, v) (bio-)degradability. However, consolidating all these properties into a single functional solution is not always straightforward. Therefore, the objective of this review paper is to present various methods for acquiring and improving PEDOT:PSS properties, with the primary focus on ensuring its biocompatibility, and simultaneously addressing the other functional features. The last section highlights a collection of designated studies, with a particular emphasis on PEDOT:PSS/carbon filler composites due to their exceptional characteristics.

Sialic acid biosensing by post-printing modification of PEDOT:PSS with pyridylboronic acid

A poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based conducting polymer, which has biorecognition capabilities, has promising biosensing applications. Previously, we developed a facile method for post-printing chemical modification of PEDOT:PSS thin films from commercial sources. Molecular recognition elements were directly introduced into the PSS side chain by a two-step chemical reaction: introduction of an ethylenediamine linker via an acid chloride reaction of the sulfonate moiety, and subsequent receptor attachment to the linker via amine coupling. In this study, the same method was used to introduce 6-carboxypyridine-3-boronic acid (carboxy-PyBA) into the linker for specifically detecting N-acetylneuraminic acid (sialic acid, SA), as a cancer biomarker. The surface-modified PEDOT:PSS films were characterized by X-ray photoelectron spectroscopy, attenuated total reflection Fourier-transform infrared spectroscopy, and static water contact angle and conductivity measurements. The specific interaction between PyBA and SA was detected by label-free reagent-free potentiometry. The SA-specific negative potential responses of modified PEDOT:PSS electrodes, which was ascribed to an SA carboxyl anion, were observed in a physiologically relevant SA range (1.6-2.9 mM) at pH 5, in a concentration-dependent manner even in the presence of 10% fetal bovine serum. The sensitivity was -2.9 mV/mM in 1-5 mM SA with a limit of detection of 0.7 mM. The sensing performances were almost equivalent to those of existing graphene-based electrical SA sensors. These results show that our chemical derivatization method for printing PEDOT:PSS thin films will have applications in SA clinical diagnostics.

Organic electronic transmembrane device for hosting and monitoring 3D cell cultures

3D cell models have made strides in the past decades in response to failures of 2D cultures to translate targets during the drug discovery process. Here, we report on a novel multiwell plate bioelectronic platform, namely, the e-transmembrane, capable of supporting and monitoring complex 3D cell architectures. Scaffolds made of PEDOT:PSS [poly(3,4-ethylenedioxythiophene):polystyrene sulfonate] are microengineered to function as separating membranes for compartmentalized cell cultures, as well as electronic components for real-time in situ recordings of cell growth and function. Owing to the high surface area-to-volume ratio, the e-transmembrane allows generation of deep, stratified tissues within the porous bulk and cell polarization at the apico-basal domains. Impedance spectroscopy measurements carried out throughout the tissue growth identified signatures from different cellular systems and allowed extraction of critical functional parameters. This platform has the potential to become a universal tool for biologists for the next generation of high-throughput drug screening assays.

Advanced Materials and Sensors for Microphysiological Systems: Focus on Electronic and Electrooptical Interfaces

Advanced in vitro cell culture systems or microphysiological systems (MPSs), including microfluidic organ-on-a-chip (OoC), are breakthrough technologies in biomedicine. These systems recapitulate features of human tissues outside of the body. They are increasingly being used to study the functionality of different organs for applications such as drug evolutions, disease modeling, and precision medicine. Currently, developers and endpoint users of these in vitro models promote how they can replace animal models or even be a better ethically neutral and humanized alternative to study pathology, physiology, and pharmacology. Although reported models show a remarkable physiological structure and function compared to the conventional 2D cell culture, they are almost exclusively based on standard passive polymers or glass with none or minimal real-time stimuli and readout capacity. The next technology leap in reproducing in vivo-like functionality and real-time monitoring of tissue function could be realized with advanced functional materials and devices. This review describes the currently reported electronic and optical advanced materials for sensing and stimulation of MPS models. In addition, an overview of multi-sensing for Body-on-Chip platforms is given. Finally, one gives the perspective on how advanced functional materials could be integrated into in vitro systems to precisely mimic human physiology.

Biostack: Nontoxic Metabolite Detection from Live Tissue

There is increasing demand for direct in situ metabolite monitoring from cell cultures and in vivo using implantable devices. Electrochemical biosensors are commonly preferred due to their low-cost, high sensitivity, and low complexity. Metabolite detection, however, in cultured cells or sensitive tissue is rarely shown. Commonly, glucose sensing occurs indirectly by measuring the concentration of hydrogen peroxide, which is a by-product of the conversion of glucose by glucose oxidase. However, continuous production of hydrogen peroxide in cell media with high glucose is toxic to adjacent cells or tissue. This challenge is overcome through a novel, stacked enzyme configuration. A primary enzyme is used to provide analyte sensitivity, along with a secondary enzyme which converts H₂ O₂ back to O₂ . The secondary enzyme is functionalized as the outermost layer of the device. Thus, production of H₂ O₂ remains local to the sensor and its concentration in the extracellular environment does not increase. This "biostack" is integrated with organic electrochemical transistors to demonstrate sensors that monitor glucose concentration in cell cultures in situ. The "biostack" renders the sensors nontoxic for cells and provides highly sensitive and stable detection of metabolites.

Organic Bioelectronics for In Vitro Systems

Bioelectronics have made strides in improving clinical diagnostics and precision medicine. The potential of bioelectronics for bidirectional interfacing with biology through continuous, label-free monitoring on one side and precise control of biological activity on the other has extended their application scope to in vitro systems. The advent of microfluidics and the considerable advances in reliability and complexity of in vitro models promise to eventually significantly reduce or replace animal studies, currently the gold standard in drug discovery and toxicology testing. Bioelectronics are anticipated to play a major role in this transition offering a much needed technology to push forward the drug discovery paradigm. Organic electronic materials, notably conjugated polymers, having demonstrated technological maturity in fields such as solar cells and light emitting diodes given their outstanding characteristics and versatility in processing, are the obvious route forward for bioelectronics due to their biomimetic nature, among other merits. This review highlights the advances in conjugated polymers for interfacing with biological tissue in vitro, aiming ultimately to develop next generation in vitro systems. We showcase in vitro interfacing across multiple length scales, involving biological models of varying complexity, from cell components to complex 3D cell cultures. The state of the art, the possibilities, and the challenges of conjugated polymers toward clinical translation of in vitro systems are also discussed throughout.

Functionalization Strategies of PEDOT and PEDOT:PSS Films for Organic Bioelectronics Applications

Organic bioelectronics involves the connection of organic semiconductors with living organisms, organs, tissues, cells, membranes, proteins, and even small molecules. In recent years, this field has received great interest due to the development of all kinds of devices architectures, enabling the detection of several relevant biomarkers, the stimulation and sensing of cells and tissues, and the recording of electrophysiological signals, among others. In this review, we discuss recent functionalization approaches for PEDOT and PEDOT:PSS films with the aim of integrating biomolecules for the fabrication of bioelectronics platforms. As the choice of the strategy is determined by the conducting polymer synthesis method, initially PEDOT and PEDOT:PSS films preparation methods are presented. Later, a wide variety of PEDOT functionalization approaches are discussed, together with bioconjugation techniques to develop efficient organic-biological interfaces. Finally, and by making use of these approaches, the fabrication of different platforms towards organic bioelectronics devices is reviewed.

All-polymeric transient neural probe for prolonged in-vivo electrophysiological recordings

Transient bioelectronics has grown fast, opening possibilities never thought before. In medicine, transient implantable devices are interesting because they could eliminate the risks related to surgical retrieval and reduce the chronic foreign body reaction. Despite recent progress in this area, the potential of transient bioelectronics is still limited by their short functional lifetime owed to the fast dissolution rate of degradable metals, which is typically a few days or weeks. Here we report that a switch from degradable metals to an entirely polymer-based approach allows for a slower degradation process and a longer lifetime of the transient probe, thus opening new possibilities for transient medical devices. As a proof-of-concept, we fabricated all-polymeric transient neural probes that can monitor brain activity in mice for a few months, rather than a few days or weeks. Also, we extensively evaluated the foreign body reaction around the implant during the probe degradation. This kind of devices might pave the way for several applications in neuroprosthetics.

Suppression of Ionic Doping by Molecular Dopants in Conjugated Polymers for Improving Specificity and Sensitivity in Biosensing Applications

Ionic doping effects in conjugated polymers often cause nonspecific signaling and a low selectivity of bioelectronic sensing. Using remote-gate field-effect transistor characterization of molecular and ionic doping in poly(3-hexylthiophene) (P3HT) and acid-functionalized polythiophene, poly[3-(3-carboxypropyl) thiophene-2,5-diyl] (PT-COOH), we discovered that proton doping effects on the interfacial potential occurring in P3HT could be suppressed by sequentially doping P3HT by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). To be specific, intrinsic pH sensitivity shown by pure P3HT (18 mV/pH in a range from pH 3 to 9) was fully dissipated for doped P3HT:F4TCNQ. However, F4TCNQ sequential doping instead increases pH sensitivity of acid-functionalized polythiophene, PT-COOH (40 mV/pH), compared to that of a pure PT-COOH (30 mV/pH). Interactions between polythiophene backbone and side chains, which constrain the activity of COOH, are weakened by stronger F4TCNQ doping leaving behind responsive COOH groups exposed to aqueous solutions. This is supported by the reduced pH sensitivity of PT-COOH sequentially doped by a weaker dopant, tetracyanoethylene (TCNE) (21 mV/pH). Thus, doping is shown to stabilize a nonpolar conjugated polymer to pH-induced fluctuations on one hand, and to activate a COOH side chain to pH-induced response on the other.

Organic Microbial Electrochemical Transistor Monitoring Extracellular Electron Transfer

Extracellular electron transfer (EET) denotes the process of microbial respiration with electron transfer to extracellular acceptors and has been exploited in a range of microbial electrochemical systems (MESs). To further understand EET and to optimize the performance of MESs, a better understanding of the dynamics at the microscale is needed. However, the real-time monitoring of EET at high spatiotemporal resolution would require sophisticated signal amplification. To amplify local EET signals, a miniaturized bioelectronic device, the so-called organic microbial electrochemical transistor (OMECT), is developed, which includes Shewanella oneidensis MR-1 integrated onto organic electrochemical transistors comprising poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) combined with poly(vinyl alcohol) (PVA). Bacteria are attached to the gate of the transistor by a chronoamperometric method and the successful attachment is confirmed by fluorescence microscopy. Monitoring EET with the OMECT configuration is achieved due to the inherent amplification of the transistor, revealing fast time-responses to lactate. The limits of detection when using microfabricated gates as charge collectors are also investigated. The work is a first step toward understanding and monitoring EET in highly confined spaces via microfabricated organic electronic devices, and it can be of importance to study exoelectrogens in microenvironments, such as those of the human microbiome.

A water-based and metal-free dye solar cell exceeding 7% efficiency using a cationic poly(3,4-ethylenedioxythiophene) derivative

A green, efficient and stable solar cell based only on water and safe and cheap elements of the periodic table is proposed in this work, finally consolidating (also from a sustainability viewpoint) the concept of "artificial photosynthesis" studied for decades by the scientific community. The concept of dye-sensitized solar cells is re-proposed here with a metal-free organic dye, an iodine-based electrolyte in a 100% aqueous environment and a new cathode (cationic PEDOT) synthesized for the first time with the aim of inhibiting the repulsion between the anions of redox couples and the PEDOT:PSS matrix commonly used as the counter-electrode. This elegant setup leads to a record efficiency of 7.02%, the highest value ever obtained for a water-based solar cell and, in general, for a photovoltaic device free of both organic solvents and expensive/heavy metals.

Instrumented Microphysiological Systems for Real-Time Measurement and Manipulation of Cellular Electrochemical Processes

Recent advancements in electronic materials and subsequent surface modifications have facilitated real-time measurements of cellular processes far beyond traditional passive recordings of neurons and muscle cells. Specifically, the functionalization of conductive materials with ligand-binding aptamers has permitted the utilization of traditional electronic materials for bioelectronic sensing. Further, microfabrication techniques have better allowed microfluidic devices to recapitulate the physiological and pathological conditions of complex tissues and organs in vitro or microphysiological systems (MPS). The convergence of these models with advances in biological/biomedical microelectromechanical systems (BioMEMS) instrumentation has rapidly bolstered a wide array of bioelectronic platforms for real-time cellular analytics. In this review, we provide an overview of the sensing techniques that are relevant to MPS development and highlight the different organ systems to integrate instrumentation for measurement and manipulation of cellular function. Special attention is given to how instrumented MPS can disrupt the drug development and fundamental mechanistic discovery processes.

Functionalized Organic Thin Film Transistors for Biosensing

The rise of organic bioelectronics efficiently bridges the gap between semiconductor devices and biological systems, leading to flexible, lightweight, and low-cost organic bioelectronic devices suitable for health or body signal monitoring. The introduction of organic semiconductors in the devices can soften the boundaries between microelectronic systems and dynamically active cells and tissues. Therefore, organic bioelectronics has attracted much attention recently due to the unique properties and promising applications. Organic thin film transistors (OTFTs), owing to their inherent capability of amplifying received signals, have emerged as one of the state-of-the-art biosensing platforms. The advantages of organic semiconductors in terms of synthetic freedom, low temperature solution processing, biocompatibility, and mechanical flexibility render OTFTs ideal transducers for wearable electronics, e-skin, and implantable devices. How to realize highly sensitive, selective, rapid, and efficient signal capture and extraction of biological recognition events is the major challenge in the design of biosensors. OTFTs are prone to converting the presence or change of target analytes into specific electrical signals even in complex biological systems. More importantly, OTFT sensors can be conveniently functionalized with chemical or biological modifications and exhibit substantially improved device sensitivity and selectivity as well as other analytical figure of merits, including calibration range, linearity, and accuracy. However, the stability and reproducibility of the organic devices need to be further improved. In this Account, we first introduce the unique features of OTFTs for bioelectronic applications. Two typical OTFT configurations, including organic electrochemical transistor (OECT) and electrolyte gated organic field effect transistor (EGOFET), are highlighted in their sensing applications mainly due to the operation of the devices in electrolytes and the combination of ionic and electronic charge transports in the devices. These devices are potentiometric transducers with low working voltages (<1 V) and high sensitivity, and are thus suitable for wearable applications with low power consumption. Second, the functionalization strategies on channel materials, electrolytes, and gate electrodes based on various modification methods and sensing mechanisms are discussed in sequence. In an OECT- or EGOFET-based biosensor, the device performance is particularly sensitive to the physical properties of the two interfaces, including channel/electrolyte and gate/electrolyte interfaces. Any change in the potential drop or capacitance of either interface can influence the channel current substantially. Therefore, the functionalization of the interfaces is critical to the sensing performance. In particular, when an electrochemically active material is modified on the interfaces, the reaction of the analyte catalyzed by the modified material can influence the interface potential and lead to a channel current response much stronger than that of a conventional electrochemical measurement. So the biosensors are much more sensitive than typical analytical methods due to the signal amplification of the transistors. Third, the processing techniques including screen printing and inkjet printing and the possibility for mass production are discussed. The applications of organic transistors in wearable electronics and healthcare monitoring systems, especially the fabric OECT-based biosensors for noninvasive detection, are presented. It is expected that the versatile organic transistors will enable various compact, flexible and disposable biosensors compatible with wearable electronics.

Functional Sensing Interfaces of PEDOT:PSS Organic Electrochemical Transistors for Chemical and Biological Sensors: A Mini Review

Organic electrochemical transistors (OECTs) are promising devices for applications in in vitro and in vivo measurements. OECTs have two important sensing interfaces for signal monitoring: One is the gate electrode surface; the other is the channel surface. This mini review introduced the new developments in chemical and biological detection of the two sensing interfaces. Specific focus was given on the modification technological approaches of the gate or channel surface. In particular, some unique strategies and surface designs aiming to facilitate signal-transduction and amplification were discussed. Several perspectives and current challenges of OECTs development were also briefly summarized.

Active Materials for Organic Electrochemical Transistors

The organic electrochemical transistor (OECT) is a device capable of simultaneously controlling the flow of electronic and ionic currents. This unique feature renders the OECT the perfect technology to interface man-made electronics, where signals are conveyed by electrons, with the world of the living, where information exchange relies on chemical signals. The function of the OECT is controlled by the properties of its core component, an organic conductor. Its chemical structure and interactions with electrolyte molecules at the nanoscale play a key role in regulating OECT operation and performance. Herein, the latest research progress in the design of active materials for OECTs is reviewed. Particular focus is given on the conducting polymers whose properties lead to advances in understanding the OECT working mechanism and improving the interface with biological systems for bioelectronics. The methods and device models that are developed to elucidate key relations between the structure of conducting polymer films and OECT function are discussed. Finally, the requirements of OECT design for in vivo applications are briefly outlined. The outcomes represent an important step toward the integration of organic electronic components with biological systems to record and modulate their functions.

Self-assembled monolayers in organic electronics

Self-assembly is possibly the most effective and versatile strategy for surface functionalization. Self-assembled monolayers (SAMs) can be formed on (semi-)conductor and dielectric surfaces, and have been used in a variety of technological applications. This work aims to review the strategy behind the design and use of self-assembled monolayers in organic electronics, discuss the mechanism of interaction of SAMs in a microscopic device, and highlight the applications emerging from the integration of SAMs in an organic device. The possibility of performing surface chemistry tailoring with SAMs constitutes a versatile approach towards the tuning of the electronic and morphological properties of the interfaces relevant to the response of an organic electronic device. Functionalisation with SAMs is important not only for imparting stability to the device or enhancing its performance, as sought at the early stages of development of this field. SAM-functionalised organic devices give rise to completely new types of behavior that open unprecedented applications, such as ultra-sensitive label-free biosensors and SAM/organic transistors that can be used as robust experimental gauges for studying charge tunneling across SAMs.

Poly(3,4-ethylenedioxythiophene)-Based Nanofiber Mats as an Organic Bioelectronic Platform for Programming Multiple Capture/Release Cycles of Circulating Tumor Cells

In this investigation, we employed a novel one-step electrospinning process to fabricate poly(ethylene oxide) (PEO)/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) core/shell nanofiber structures with improved water resistance and good electrochemical properties and characterized them using scanning electron microscopy, transmission electron microscopy, and time-of-flight secondary ion mass spectrometry imaging. We then integrated a biotinylated poly-(l-lysine-graft-ethylene glycol) (PLL-g-PEG-biotin) coating with three-dimensional (3D) PEDOT-based nanofiber devices for dynamic control over the capture/release performance of rare circulating tumor cells (CTCs) on-chip. The detailed capture/release behavior of the circulating tumor cells was studied using an organic bioelectronic platform comprising PEO/PEDOT:PSS nanofiber mats with 3 wt % (3-glycidyloxypropyl)trimethoxysilane as an additive. We have demonstrated that these nanofiber mats deposited on five-patterned indium tin oxide finger electrodes are excellent candidates for use as functional bioelectronic interfaces for the isolation, detection, sequential collection, and enrichment of rare CTCs through electrical activation of each single electrode. This combination behaved as an ideal model system displaying a high cell-capture yield for antibody-positive cells while resisting the adhesion of antibody-negative cells. Taking advantage of the electrochemical doping/dedoping characteristics of PEDOT:PSS materials, the captured rare cells could be electrically triggered release through the desorption phenomena of PLL-g-PEG-biotin on device surface. More than 90% of the targeted cancer cells were captured on the 3D PEDOT-based nanofiber microfluidic device; over 87% of captured cancer cells were subsequently released for collection; approximately 80% of spiked cancer cells could be collected in a 96-well plate. Therefore, this 3D PEDOT-based nanofiber approach appears to be an economical route for the large-scale preparation of systems for enhancing the downstream characterization of rare CTCs.

Organic transistor platform with integrated microfluidics for in-line multi-parametric in vitro cell monitoring

Future drug discovery and toxicology testing could benefit significantly from more predictive and multi-parametric readouts from in vitro models. Despite the recent advances in the field of microfluidics, and more recently organ-on-a-chip technology, there is still a high demand for real-time monitoring systems that can be readily embedded with microfluidics. In addition, multi-parametric monitoring is essential to improve the predictive quality of the data used to inform clinical studies that follow. Here we present a microfluidic platform integrated with in-line electronic sensors based on the organic electrochemical transistor. Our goals are two-fold, first to generate a platform to host cells in a more physiologically relevant environment (using physiologically relevant fluid shear stress (FSS)) and second to show efficient integration of multiple different methods for assessing cell morphology, differentiation, and integrity. These include optical imaging, impedance monitoring, metabolite sensing, and a wound-healing assay. We illustrate the versatility of this multi-parametric monitoring in giving us increased confidence to validate the improved differentiation of cells toward a physiological profile under FSS, thus yielding more accurate data when used to assess the effect of drugs or toxins. Overall, this platform will enable high-content screening for in vitro drug discovery and toxicology testing and bridges the existing gap in the integration of in-line sensors in microfluidic devices.

Lactate Detection in Tumor Cell Cultures Using Organic Transistor Circuits

A biosensing platform based on an organic transistor circuit for metabolite detection in highly complex biological media is introduced. The sensor circuit provides inherent background subtraction allowing for highly specific, sensitive lactate detection in tumor cell cultures. The proposed sensing platform paves the way toward rapid, label-free, and cost-effective clinically relevant in vitro diagnostic tools.

Polyelectrolyte Layer-by-Layer Assembly on Organic Electrochemical Transistors

Oppositely charged polyelectrolyte multilayers (PEMs) were built up in a layer-by-layer (LbL) assembly on top of the conducting polymer channel of an organic electrochemical transistor (OECT), aiming to combine the advantages of well-established PEMs with a high performance electronic transducer. The multilayered film is a model system to investigate the impact of biofunctionalization on the operation of OECTs comprising a poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) film as the electrically active layer. Understanding the mechanism of ion injection into the channel that is in direct contact with charged polymer films provides useful insights for novel biosensing applications such as nucleic acid sensing. Moreover, LbL is demonstrated to be a versatile electrode modification tool enabling tailored surface features in terms of thickness, softness, roughness, and charge. LbL assemblies built up on top of conducting polymers will aid the design of new bioelectronic platforms for drug delivery, tissue engineering, and medical diagnostics.

Synthesis of Hetero-bifunctional, End-Capped Oligo-EDOT Derivatives

Conjugated oligomers of 3,4-ethylenedioxythiophene (EDOT) are attractive materials for tissue engineering applications and as model systems for studying the properties of the widely used polymer poly(3,4-ethylenedioxythiophene). We report here the facile synthesis of a series of keto-acid end-capped oligo-EDOT derivatives (n = 2-7) through a combination of a glyoxylation end-capping strategy and iterative direct arylation chain extension. Importantly, these structures not only represent the longest oligo-EDOTs reported but are also bench stable, in contrast to previous reports on such oligomers. The constructs reported here can undergo subsequent derivatization for integration into higher-order architectures, such as those required for tissue engineering applications. The synthesis of hetero-bifunctional constructs, as well as those containing mixed-monomer units, is also reported, allowing further complexity to be installed in a controlled manner. Finally, we describe the optical and electrochemical properties of these oligomers and demonstrate the importance of the keto-acid in determining their characteristics.

Organic Transistor Arrays Integrated with Finger-Powered Microfluidics for Multianalyte Saliva Testing

A compact multianalyte biosensing platform is reported, composed of an organic electrochemical transistor (OECT) microarray integrated with a pumpless "finger-powered" microfluidic, for quantitative screening of glucose, lactate, and cholesterol levels. A biofunctionalization method is designed, which provides selectivity towards specific metabolites as well as minimization of any background interference. In addition, a simple method is developed to facilitate multi-analyte sensing and avoid electrical crosstalk between the different transistors by electrically isolating the individual devices. The resulting biosensing platform, verified using human samples, offers the possibility to be used in easy-to-obtain biofluids with low abundance metabolites, such as saliva. Based on our proposed method, other types of enzymatic biosensors can be integrated into the array to achieve multiplexed, noninvasive, personalized point-of-care diagnostics.

Biofunctionalization of polydioxythiophene derivatives for biomedical applications

It is becoming clear that development of biomedical devices relies on engineering of the interface between the device and the biological component. Improved performance for these sensors and devices can be achieved through biofunctionalization. In this review we focus on highlighting the biofunctionalization of polydioxythiophene sensors.

Size-controllable ultrathin carboxylated polypyrrole nanotube transducer for extremely sensitive 17β-estradiol FET-type biosensors

Size-controllable aptamer conjugated ultrathin carboxylated polypyrrole nanotubes (A-UCPPyNTs) were successfully fabricated as transducers in 17β-estradiol field-effect transistor (FET)-type biosensors which has extremely high sensitivity (∼1 fM) and unique selectivity.

A lysinated thiophene-based semiconductor as a multifunctional neural bioorganic interface

Lysinated molecular organic semiconductors are introduced as valuable multifunctional platforms for neural cells growth and interfacing. Cast films of quaterthiophene (T4) semiconductor covalently modified with lysine-end moieties (T4Lys) are fabricated and their stability, morphology, optical/electrical, and biocompatibility properties are characterized. T4Lys films exhibit fluorescence and electronic transport as generally observed for unsubstituted oligothiophenes combined to humidity-activated ionic conduction promoted by the charged lysine-end moieties. The Lys insertion in T4 enables adhesion of primary culture of rat dorsal root ganglion (DRG), which is not achievable by plating cells on T4. Notably, on T4Lys, the number on adhering neurons/area is higher and displays a twofold longer neurite length than neurons plated on glass coated with poly-l-lysine. Finally, by whole-cell patch-clamp, it is shown that the biofunctionality of neurons cultured on T4Lys is preserved. The present study introduces an innovative concept for organic material neural interface that combines optical and iono-electronic functionalities with improved biocompatibility and neuron affinity promoted by Lys linkage and the softness of organic semiconductors. Lysinated organic semiconductors could set the scene for the fabrication of simplified bioorganic devices geometry for cells bidirectional communication or optoelectronic control of neural cells biofunctionality.

Integrated 3D conducting polymer-based bioelectronics for capture and release of circulating tumor cells

Here we develop a novel fabrication approach for producing three-dimensional (3D) conducting polymer-based bioelectronic interfaces (BEIs) that can be integrated on electronic devices for rare circulating tumor cell (CTC) isolation, detection, and collection via an electrically triggered cell released from chips. Based on the chemical oxidative polymerization of carboxylic acid-modified 3,4-ethylenedioxythiophene and modified poly(dimethylsiloxane) (PDMS) transfer printing technology, the high-aspect-ratio structures of poly(3,4-ethylenedioxythiophene) (PEDOT)-based "nanorod" arrays can be fabricated on indium tin oxide (ITO) electrodes when using the Si "microrod" arrays as masters. Furthermore, we integrated the biotinylated poly-(l)-lysine-graft-poly-ethylene-glycol (PLL-g-PEG-biotin) coating with 3D PEDOT-based BEIs for dynamic control of the capture/release performance of CTCs on chips; this combination exhibited an optimal cell-capture yield cells of ∼45 000 cells cm^-2 from EpCAM-positive MCF7 while maintaining resistance from the adhesion of EpCAM-negative HeLa cells at a density of ∼4000 cells cm^-2. By taking advantage of the electrochemical doping/dedoping properties of PEDOT materials, the captured CTCs can be triggered to be electrically released through the desorption phenomena of the PLL-g-PEG-biotin. More than 90% of the captured cells can be released while maintaining very high cell viability. Therefore, it is conceivable that the use of a 3D PEDOT-based BEI platform will meet the requirements for the development of downstream characterization of CTCs, as well as the next generation of bioelectronics for biomedical applications.

Rigid and flexible organic electrochemical transistor arrays for monitoring action potentials from electrogenic cells

Rigid and flexible organic electrochemical transistor arrays are successfully implemented for monitoring cardiac action potentials. Excellent signal to noise ratios are achieved with values routinely larger than 4. These devices are promising to be used in both conventional and emerging areas.

A simple approach for protein covalent grafting on conducting polymer films

By mixing a PEDOT:PSS suspension with the modified biopolymer carboxymethylated dextran (CMD), we obtain conductive films displaying carboxyl (–COOH) groups allowing for covalent grafting of proteins via amide bonds.

Combined optical and electronic sensing of epithelial cells using planar organic transistors

A planar, conducting-polymer-based transistor for combined optical and electronic monitoring of live cells provides a unique platform for monitoring the health of cells in vitro. Monitoring of MDCK-I epithelial cells over several days is shown, along with a demonstration of the device for toxicology studies, of use in future drug discovery or diagnostics applications.