Benchmarking organic mixed conductors for transistors.

Organic mixed conductors have garnered significant attention in applications from bioelectronics to energy storage/generation. Their implementation in organic transistors has led to enhanced biosensing, neuromorphic function, and specialized circuits. While a narrow class of conducting polymers continues to excel in these new applications, materials design efforts have accelerated as researchers target new functionality, processability, and improved performance/stability. Materials for organic electrochemical transistors (OECTs) require both efficient electronic transport and facile ion injection in order to sustain high capacity. In this work, we show that the product of the electronic mobility and volumetric charge storage capacity (µC*) is the materials/system figure of merit; we use this framework to benchmark and compare the steady-state OECT performance of ten previously reported materials. This product can be independently verified and decoupled to guide materials design and processing. OECTs can therefore be used as a tool for understanding and designing new organic mixed conductors

Hydroxymethyl PEDOT microstructure-based electrodes for high-performance supercapacitors

The development of conducting polymer-based supercapacitors offers remarkable advantages, such as good ionic and electronic conductivity, ease of synthesis, low processing cost, and mechanical flexibility. 3,4-ethylenedioxythiophene (PEDOT) is a conducting polymer with robust chemical and environmental stability during storage and operation in an aqueous environment. Yet, improving its electrochemical capacitance and cycle life remains a challenge for high-performance supercapacitors exceeding the current state-of-the-art. The fabrication of PEDOT composites with carbon nanomaterials and metal oxides is the commonly used approach to enhance capacitance and stability. This work discusses a comparative study to fabricate highly stable PEDOT derivative electrodes with remarkable specific capacitance via a straightforward electrochemical polymerization technique. The hydroxymethyl PEDOT (PEDOTOH) doped with perchlorate in a dichloromethane (DCM) solvent (197 F g−1) exhibits superior performance compared to the polymer formed in an aqueous solution (124 F g−1). Furthermore, the electropolymerized PEDOTOH on flexible Au/Kapton substrates was assembled into a free-standing symmetrical supercapacitor in an agarose additive-free gel. The use of agarose gel electrolytes can offer easy handling, no leakage, moderate ionic conductivity, and flexibility for miniaturization and integration. The supercapacitor reached a specific capacitance of 36.96 F g−1 at a current density of 13.7 A g−1, an energy density of 14.96 Wh kg−1, and a power density of 22.2 kW kg−1 among the highest values reported for PEDOT-based supercapacitors. The self-standing supercapacitor achieves an industry-par capacitance retention of ∼98% after 10000 charge/discharge cycles at 10 A g−1. This study provides insights into the effect of solvents and electropolymerization modes on the polymer structure and its electrochemical properties toward high-performance supercapacitor devices

Structure-related differences in the temperature-regulated fluorescence response of LCST type polymers

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.We demonstrate new fluorophore-labelled materials based on acrylamide and on oligo(ethylene glycol) (OEG) bearing thermoresponsive polymers for sensing purposes and investigate their thermally induced solubility transitions. It is found that the emission properties of the polarity-sensitive (solvatochromic) naphthalimide derivative attached to three different thermoresponsive polymers are highly specific to the exact chemical structure of the macromolecule. While the dye emits very weakly below the LCST when incorporated into poly(N-isopropylacrylamide) (pNIPAm) or into a polyacrylate backbone bearing only short OEG side chains, it is strongly emissive in polymethacrylates with longer OEG side chains. Heating of the aqueous solutions above their cloud point provokes an abrupt increase of the fluorescence intensity of the labelled pNIPAm, whereas the emission properties of the dye are rather unaffected as OEG-based polyacrylates and methacrylates undergo phase transition. Correlated with laser light scattering studies, these findings are ascribed to the different degrees of pre-aggregation of the chains at low temperatures and to the extent of dehydration that the phase transition evokes. It is concluded that although the temperature-triggered changes in the macroscopic absorption characteristics, related to large-scale alterations of the polymer chain conformation and aggregation, are well detectable and similar for these LCST-type polymers, the micro-environment provided to the dye within each polymer network differs substantially. Considering sensing applications, this finding is of great importance since the temperature-regulated fluorescence response of the polymer depends more on the macromolecular architecture than the type of reporter fluorophore.BMBF, 03IS2201B, Spitzenforschung und Innovation in den Neuen Ländern - Das Taschentuchlabor: Impulszentrum für Integrierte Bioanalyse (IZIB

An Electrocorticography Device with an Integrated Microfluidic Ion Pump for Simultaneous Neural Recording and Electrophoretic Drug Delivery In Vivo

The challenge of treating neurological disorders has motivated the development of implantable devices that can deliver treatment when and where it’s needed. This study presents a novel brain implant capable of electrophoretically delivering drugs and recording local neural activity on the surface of the brain. The drug delivery is made possible by the integration of a microfluidic ion pump (µFIP) into a conformable electrocorticography (ECoG) device with recording cites embedded next to the drug delivery outlets. The µFIP ECoG device can deliver a high capacity of several biologically important cationic species on demand. The therapeutic potential of the device is demonstrated by using it to deliver neurotransmitters in a rodent model while simultaneously recording local neural activity. These developments represent a significant step forward for cortical drug-delivery systems

Integration of Organic Electrochemical Transistors with Implantable Probes

Funder: King Abdullah University of Science and Technology; Id: http://dx.doi.org/10.13039/501100004052Abstract: Organic electrochemical transistors (OECTs) are widely used as amplifying transducers of biological signals due to their high transconductance and biocompatibility. For implantable applications that penetrate into tissue, OECTs need to be integrated onto narrow probes. The scarcity of real estate necessitates the use of small local gate electrodes and narrow interconnects. This work shows that both of these factors lead to a decrease in the maximum transconductance and an increase in gate voltage required to attain this maximum. This work further shows that coating the gate electrode with a thick conducting polymer improves performance. These findings help guide the development of efficient OECTs on implantable probes

Conjugated Polymers in Bioelectronics.

The emerging field of organic bioelectronics bridges the electronic world of organic-semiconductor-based devices with the soft, predominantly ionic world of biology. This crosstalk can occur in both directions. For example, a biochemical reaction may change the doping state of an organic material, generating an electronic readout. Conversely, an electronic signal from a device may stimulate a biological event. Cutting-edge research in this field results in the development of a broad variety of meaningful applications, from biosensors and drug delivery systems to health monitoring devices and brain-machine interfaces. Conjugated polymers share similarities in chemical "nature" with biological molecules and can be engineered on various forms, including hydrogels that have Young's moduli similar to those of soft tissues and are ionically conducting. The structure of organic materials can be tuned through synthetic chemistry, and their biological properties can be controlled using a variety of functionalization strategies. Finally, organic electronic materials can be integrated with a variety of mechanical supports, giving rise to devices with form factors that enable integration with biological systems. While these developments are innovative and promising, it is important to note that the field is still in its infancy, with many unknowns and immense scope for exploration and highly collaborative research. The first part of this Account details the unique properties that render conjugated polymers excellent biointerfacing materials. We then offer an overview of the most common conjugated polymers that have been used as active layers in various organic bioelectronics devices, highlighting the importance of developing new materials. These materials are the most popular ethylenedioxythiophene derivatives as well as conjugated polyelectrolytes and ion-free organic semiconductors functionalized for the biological interface. We then discuss several applications and operation principles of state-of-the-art bioelectronics devices. These devices include electrodes applied to sense/trigger electrophysiological activity of cells as well as electrolyte-gated field-effect and electrochemical transistors used for sensing of biochemical markers. Another prime application example of conjugated polymers is cell actuators. External modulation of the redox state of the underlying conjugated polymer films controls the adhesion behavior and viability of cells. These smart surfaces can be also designed in the form of three-dimensional architectures because of the processability of conjugated polymers. As such, cell-loaded scaffolds based on electroactive polymers enable integrated sensing or stimulation within the engineered tissue itself. A last application example is organic neuromorphic devices, an alternative computing architecture that takes inspiration from biology and, in particular, from the way the brain works. Leveraging ion redistribution inside a conjugated polymer upon application of an electrical field and its coupling with electronic charges, conjugated polymers can be engineered to act as artificial neurons or synapses with complex, history-dependent behavior. We conclude this Account by highlighting main factors that need to be considered for the design of a conjugated polymer for applications in bioelectronics-although there can be various figures of merit given the broad range of applications, as emphasized in this Account

Direct metabolite detection with an n-type accumulation mode organic electrochemical transistor.

The inherent specificity and electrochemical reversibility of enzymes poise them as the biorecognition element of choice for a wide range of metabolites. To use enzymes efficiently in biosensors, the redox centers of the protein should have good electrical communication with the transducing electrode, which requires either the use of mediators or tedious biofunctionalization approaches. We report an all-polymer micrometer-scale transistor platform for the detection of lactate, a significant metabolite in cellular metabolic pathways associated with critical health care conditions. The device embodies a new concept in metabolite sensing where we take advantage of the ion-to-electron transducing qualities of an electron-transporting (n-type) organic semiconductor and the inherent amplification properties of an ion-to-electron converting device, the organic electrochemical transistor. The n-type polymer incorporates hydrophilic side chains to enhance ion transport/injection, as well as to facilitate enzyme conjugation. The material is capable of accepting electrons of the enzymatic reaction and acts as a series of redox centers capable of switching between the neutral and reduced state. The result is a fast, selective, and sensitive metabolite sensor. The advantage of this device compared to traditional amperometric sensors is the amplification of the input signal endowed by the electrochemical transistor circuit and the design simplicity obviating the need for a reference electrode. The combination of redox enzymes and electron-transporting polymers will open up an avenue not only for the field of biosensors but also for the development of enzyme-based electrocatalytic energy generation/storage devices

Electroconductive Hydrogel Based on Functional Poly(Ethylenedioxy Thiophene).

Poly(ethylene dioxythiophene) with functional pendant groups bearing double bonds is synthesized and employed for the fabrication of electroactive hydrogels with advantageous characteristics: covalently cross-linked porous 3D scaffolds with notable swelling ratio, appropriate mechanical properties, electroactivity in physiological conditions, and suitability for proliferation and differentiation of C2C12 cells. This is a new approach for the fabrication of conductive engineered constructs

The Role of Side Chains and Hydration on Mixed Charge Transport in <i>n</i> ‐Type Polymer Films

Introducing ethylene glycol (EG) side chains to a conjugated polymer backbone is a well‐established synthetic strategy for designing organic mixed ion‐electron conductors (OMIECs). However, the impact that film swelling has on mixed conduction properties has yet to be scoped, particularly for electron‐transporting (n‐type) OMIECs. Here, the authors investigate the effect of the length of branched EG chains on mixed charge transport of n‐type OMIECs based on a naphthalene‐1,4,5,8‐tetracarboxylic‐diimide‐bithiophene backbone. Atomic force microscopy (AFM), grazing‐incidence wide‐angle X‐ray scattering (GIWAXS), and scanning tunneling microscopy (STM) are used to establish the similarities between the common‐backbone films in dry conditions. Electrochemical quartz crystal microbalance with dissipation monitoring (EQCM‐D) and in situ GIWAXS measurements reveal stark changes in film swelling properties and microstructure during electrochemical doping, depending on the side chain length. It is found that even in the loss of the crystallite content upon contact with the aqueous electrolyte, the films can effectively transport charges and that it is rather the high water content that harms the electronic interconnectivity within the OMIEC films. These results highlight the importance of controlling water uptake in the films to impede charge transport in n‐type electrochemical devices

Water stable molecular n-doping produces organic electrochemical transistors with high transconductance and record stability.

From established to emergent technologies, doping plays a crucial role in all semiconducting devices. Doping could, theoretically, be an excellent technique for improving repressively low transconductances in n-type organic electrochemical transistors - critical for advancing logic circuits for bioelectronic and neuromorphic technologies. However, the technical challenge is extreme: n-doped polymers are unstable in electrochemical transistor operating environments, air and water (electrolyte). Here, the first demonstration of doping in electron transporting organic electrochemical transistors is reported. The ammonium salt tetra-n-butylammonium fluoride is simply admixed with the conjugated polymer poly(N,N'-bis(7-glycol)-naphthalene-1,4,5,8-bis(dicarboximide)-co-2,2'-bithiophene-co-N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide), and found to act as a simultaneous molecular dopant and morphology-additive. The combined effects enhance the n-type transconductance with improved channel capacitance and mobility. Furthermore, operational and shelf-life stability measurements showcase the first example of water-stable n-doping in a polymer. Overall, the results set a precedent for doping/additives to impact organic electrochemical transistors as powerfully as they have in other semiconducting devices