Xenofon Strakosas

In electroencephalography, hair remains a major barrier to electrode-skin contact, limiting signal quality. Here, we introduce electronic hair (eHAIR), a strategy that converts hair into a bioelectronic interface using mixed ionic-electronic conductive polymer dyes. Hair, a keratinized filament anchored within the skin, provides a stable and naturally distributed platform for interfacing. Two complementary approaches based on polythiophene derivatives enable rapid, washable functionalization of hair bundles or semipermanent coating of individual strands. The resulting eHAIR forms conformal, low-impedance interfaces that support electrophysiological recordings with increased signal amplitude and spectral power while preserving the underlying neural dynamics without gels or rigid hardware. Beyond passive sensing, eHAIR-based organic electrochemical transistors enable local signal amplification, with gain defined by hair geometry. By repurposing hair as an active bioelectronic interface, eHAIR establishes a wearable and biointegrated platform that can be implemented from individual hairs to larger hair-covered regions.

Organic mixed ionic-electronic conductors (OMIECs) are pivotal for next-generation organic electronics and bioelectronics. However, conventional fabrication methods such as electrochemical and chemical polymerization, and spin-coating often involve complex, multi-step processes, specialized equipment, time-consuming patterning, and significant energy input. Here, we overcome these limitations by introducing a self-driven polymerization method, in which an OMIEC precursor molecule undergoes direct oxidation on a metal electrode. This simple, equipment-free approach enables rapid, in situ formation of conducting polymer coatings on a range of noble metal surfaces, including challenging architectures. This method enables one-step formation of high-performance organic electrochemical transistors with simultaneous glucose oxidase integration, directly producing a functional glucose biosensor and highlighting its potential for multifunctional devices. Importantly, we validate the performance of these high-capacitance coatings in a soft multielectrode array cuff for sciatic nerve interfacing, achieving selective electrical stimulation and high-fidelity in vivo recording. The device supports motor-selective stimulation, ultra-low stimulation saturation thresholds (25–30 µA), and reliable detection of sensory compound action potentials across multiple plantar hind paw regions. Overall, this fast, scalable, and aqueous-based approach provides a high-throughput route for fabricating advanced bioelectronic devices.

Organic bioelectronics relies on materials capable of efficiently transducing signals between ionic biological environments and electronic devices. Conducting polymers are particularly attractive for this purpose due to their mixed ionic-electronic conductivity, mechanical compliance, and chemical tunability. Among them, bis-ethylenedioxythiophene-thiophene (ETE)-based polymers can be synthesized in situ via mild enzymatic reactions, enabling seamless and substrate-free integration with biological systems. Here, we investigate the impact of hydrophilic side-chain engineering on the physicochemical, electrochemical, and biological properties of ETE-based polymers by comparing two polymers which differ only by the presence of a triethylene glycol side chain between the ETE core and the terminal carboxylic group. We show that glycolation leads to increased film hydration and surface roughness without a measurable change in elastic modulus, suggesting competing effects from molecular ordering and ionic cross-linking. In a neuronal cell model, the glycolated polymer exhibits markedly enhanced cytocompatibility and cell adhesion, likely driven by its increased surface roughness and matrix topography. By combining electrochemical quartz crystal microbalance with dissipation monitoring, in-operando UV-vis spectroscopy, and electrochemical atomic force microscopy, we correlate ionic transport, swelling behavior, and nanomechanical responses, revealing enhanced electrochemically induced swelling in the glycolated polymer. Finally, when implemented as active channel materials in organic electrochemical transistors, both polymers display comparable performance, although the glycolated polymer shows slightly reduced cycling stability. These findings highlight the complex trade-offs introduced by side-chain glycolation and provide design guidelines for enzymatically synthesized conducting polymers in bioelectronic interfaces.

INTEGRATION DE PROTEINES DANS DES TRANSISTORS ELECTROCHIMIQUES ORGANIQUES POUR DES APPLICATIONS DE BIOSENSEURS.: Le domaine de la bioélectronique, qui couple l'électronique et la biologie, présente un fort potentiel pour le développement de nouveaux outils biomédicaux. Les dispositifs à base d’électronique organique sont particulièrement prometteurs; l'utilisation de ces matériaux organiques confère une interface idéale entre les mondes biologique et électronique en raison de leur biocompatibilité et de leur possible grande flexibilité. Le transistor électrochimique organique (OECT) représente un dispositif prometteur dans ce domaine. Des OECT ont par exemple été intégrés dans des systèmes permettant de détecter localement l’activité ionique/biomoléculaire, de mesurer l'activité d'une cellule unique, mais aussi d’effectuer la caractérisation de tissus et le suivi du fonctionnement d’organes entiers. L'OECT est un dispositif extrêmement polyvalent qui apparaît comme un outil thérapeutique et de diagnostic de première importance. L'utilisation de matériaux organiques tels que les polymères conducteurs, rend l‘OECT adaptable pour une large gamme d'applications. Un exemple représentatif est le capteur de glucose. L'OECT, en raison de ses propriétés d'amplification, peut augmenter ces courants de plusieurs ordres de grandeurs. Utilisé comme capteur de glucose, il montre une forte sensibilité et des limites de détection des concentrations de l’ordre du nanomolar. Cependant, en dehors d’une meilleure précision de mesure, la stabilité est nécessaire pour les applications à long terme. Par exemple, ces capteurs se doivent d'enregistrer en continu les variations de glycémie chez des personnes pendant plusieurs jours et sans défaillance. Le glucose est la source d'énergie principale du cerveau. Ainsi, l'enregistrement de la modulation des niveaux de glucose avant et/ou pendant la crise d'épilepsie peut donner beaucoup d'informations dans la compréhension de cette maladie. Pour des applications à long termes, une liaison covalente de la biomolécule est préférable.La biofonctionnalisation des polymères conducteurs, qui sont utilisés comme matières actives dans les OECTs, est une étape obligatoire qui mettra en évidence les propriétés de l’OECT telles que la biocompatibilité, la stabilité, et la fonctionnalité. Dans ce travail, des méthodes de biofonctionnalisation du poly (3,4-éthylènedioxythiophène) dopé avec des anions de tosylate (PEDOT: TOS) ou dopé avec du poly (styrène sulfonate) (PEDOT: PSS) ont été développéeset ont conduitsent à des améliorations telles que la biocompatibilité accrue avec les cellules et à une stabilité accrue pour les applications de détection. En outre, nous avons étudié l'utilisation de liquides ioniques en combinaison avec des polymères réticulables comme alternatives aux électrolytes conventionnelles. Ces gels ioniques électrolytes ont amélioré la stabilité des enregistrements électrophysiologiques. Enfin, des mesures in vitro de l'activité métabolique de la cellule ont été effectuées. Le suivi de l'absorption du glucose et de la conversion en lactate fournit des informations sur la santé des cellules et comment ses activités métaboliques sont affectées par la présence de composés toxiques et d’agents pathogènes.

The development of robust and biocompatible interfaces between living cells and electronic devices is essential for the advancement of bioelectronic and medical technologies. Organic conjugated polymers have emerged as promising materials for this purpose owing to their mixed ion and electron conductivity, as well as their mechanical and chemical flexibility. Here, we present a simple, genetic-modification-free protocol for enzyme-mediated, cell-templated polymerization that enables the formation of conductive polymer coatings on the surface of living cells. By exploiting the non-specific adsorption of horseradish peroxidase (HRP) onto the cell membrane followed by in situ suspension polymerization of a thiophene-based monomer, we achieve localized polymeric coatings on the cell membrane without compromising cell viability or excitability. The method is successfully applied to different cell lines, and the polymer properties are successfully characterized by absorption spectroscopy, scanning electron microscopy, and conductive atomic force microscopy. Functional assays demonstrate preserved cellular responsiveness and viability, and the polymer coating remains stable for up to four days. This in situ polymerization approach offers a rapid, versatile, and minimally invasive strategy for engineering bioelectronic interfaces, expanding the toolkit for integrating electronics with living systems.

Aqueous organic redox flow batteries (AORFBs) enhance the sustainability of battery energy storage systems (BESS), supporting a greater integration of renewable electricity into the grid. We investigated the aspartate‐derived naphthalene diimide (NDI)‐based AORFB by independent monitoring of the individual electrode potentials on positive and negative electrodes. The mapping of these electrode potentials against analytically calculated states of charge (SOCs) for the negative and positive electrodes showed good agreement. This manifests the Nernstian behavior of electrode potentials defined by non‐ideal redox electrolytes. Evidence was obtained for both the re‐oxidation of charging products at the negative electrode by oxygen traces and their hydrolysis, which were conceptualized as redox shunt and irreversible degradation, respectively. The contributions of these processes to performance deterioration were illustrated using theoretical charging profiles.

Polymer‐based organic mixed ion‐electron conductors (OMIECs) are a class of materials offering unique coupled dual charge transport characteristics along with appealing properties including mechanical softness, biocompatibility, tunability, volumetric capacitance, and stability. These features have been exploited in devices including organic electrochemical transistors (OECTs), neuromorphic computing, energy storage, sensors, neural electrodes, and actuators. Conventionally, OMIEC polymers are prepared through chemical, vapor‐phase, electrochemical, or enzymatic polymerization, typically relying on oxidants, metal catalysts, and/or organic solvents, significantly limiting their scalability, sustainability, and biocompatibility. Here, we introduce an initiator‐free, visible‐light‐induced polymerization of water‐soluble conducting polymer precursors, enabling facile formation of high‐performance and inherently biocompatible OMIECs. This novel approach allows direct photopatterning and seamless film deposition and manufacturing of OECTs across rigid, flexible, and biological substrates, exemplified by glass, textiles, and mouse skin (in vivo). Through careful optimization of the photopolymerization process, resulting OMIECs possess state‐of‐the‐art electrical, electrochemical, and device properties along with exceptional compatibility and conformability with various flexible and biological surfaces. Finally, we demonstrate the utility of these photopatterned electrodes, manufactured directly on mouse skin in vivo, where they significantly enhance the recording efficacy and signal‐to‐noise ratio of low‐frequency brain activity in anesthetized mice.

Polymer‐based organic mixed ion‐electron conductors (OMIECs) are a class of materials offering unique coupled dual charge transport characteristics along with appealing properties including mechanical softness, biocompatibility, tunability, volumetric capacitance, and stability. These features have been exploited in devices including organic electrochemical transistors (OECTs), neuromorphic computing, energy storage, sensors, neural electrodes, and actuators. Conventionally, OMIEC polymers are prepared through chemical, vapor‐phase, electrochemical, or enzymatic polymerization, typically relying on oxidants, metal catalysts, and/or organic solvents, significantly limiting their scalability, sustainability, and biocompatibility. Here, we introduce an initiator‐free, visible‐light‐induced polymerization of water‐soluble conducting polymer precursors, enabling facile formation of high‐performance and inherently biocompatible OMIECs. This novel approach allows direct photopatterning and seamless film deposition and manufacturing of OECTs across rigid, flexible, and biological substrates, exemplified by glass, textiles, and mouse skin (in vivo). Through careful optimization of the photopolymerization process, resulting OMIECs possess state‐of‐the‐art electrical, electrochemical, and device properties along with exceptional compatibility and conformability with various flexible and biological surfaces. Finally, we demonstrate the utility of these photopatterned electrodes, manufactured directly on mouse skin in vivo, where they significantly enhance the recording efficacy and signal‐to‐noise ratio of low‐frequency brain activity in anesthetized mice.

Coupling biology with electronics is emerging as a transformative approach in developing advanced medical treatments, with examples ranging from implants for treating neurological disorders to biosensors for real-time monitoring of physiological parameters. The electrodes used for these purposes often face challenges such as signal degradation due to biofouling and limited biocompatibility, which can lead to inaccurate readings and tissue damage over time. Conducting organic polymers are a promising alternative because of their mechanical, chemical, and physical properties, which better match the ones of biological systems. They also can be synthesized in vivo to form bio-templated structures through biologically compatible manufacturing processes. Here, we report a method to achieve conductive polymer structures anchored to cell membranes, creating an intimate interface between the polymer electrode and single cells. We show that the polymer is nontoxic to cells and does not interfere with its activation, thereby making this process an interesting alternative to existing materials and electrode techniques.

A novel approach is introduced to modulate the threshold voltage of organic electrochemical transistors (OECTs) that are fabricated by electropolymerizing the channel material between the source and drain electrodes. To achieve this, we adjust the ratio of two water‐soluble tri‐thiophene monomers, which share the same backbone, but present either anionic or zwitterionic sidechains, during channel formation. This approach allows for a continuous modulation of both the electropolymerization onset potential and the native doping state of the film. We attribute the effect of monomer blends displaying properties that are a weighted average of their components to the formation of nanoscale monomer aggregates that have a uniform internal charge density. Through an investigation of monomer aggregation behavior, polymer film growth, and device properties of OECTs fabricated by electropolymerization, we highlight the importance of monomer aggregation in the electropolymerization of conducting polymers. The ability to tune both electropolymerization onset and the OECT threshold voltage has significant implications for the development of more complex circuits for integrated neuromorphic computing, biosensing, and bioelectronic systems.