Organic electrochemical transistors (OECTs) have attracted great attention as they hold significant promise for a variety of applications ranging from printable logic circuits for electronic textiles to drivers for sensors and flat panel display pixels, as well as to artificial synapse for neuromorphic computing. [1] Because of the low working bias, high sensitivity, and stability in aqueous environments, as well as biological and mechanical compatibility with live tissues, OECTs have also recently emerged as a technological solution to a variety of diagnostic and therapeutic applications. [2] A considerable amount of work has focused, for example, on approaches exploiting the principle of OECTs for the development of biomedical tools for chemical and biological sensing, [3] electrophysiological recording, [4] monitoring of cell viability, and barrier tissue integrity, [5] to name just a few. In an OECT, the electroactive polymer constituting the channel is in direct contact with an electrolyte and with the source and drain metal electrodes ( Figure 1A). Because of the soft and permeable nature of the electroactive polymers, ions are able to penetrate into the bulk of the transistor channel. [6] The operation of an OECT relies then on a reversible ion exchange and charge compensation process, which leads to a bulk doping of the organic conducting channel and to a modulation of the electronic conductivity between the source and drain contacts. Hence, OECTs transduce a modulation in the gate voltage (V G ) to a modulation in the drain current (I D ) running through the entire bulk of the channel. The figure-of-merit that quantifies the efficiency of this transduction is the transconductance, defined as g m = ∂I D /∂V G .The current state-of-the-art active material for OECTs is the mixed ion-electron conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The volumetric doping and dedoping of PEDOT:PSS result in a modulation of the drain-source current of several orders of magnitude with a consequent high transconductance. [7] As PEDOT:PSS is doped in its pristine state, and thus highly conducting, the OECT operates in depletion mode. In addition, several polythiophene-based polymers have been reported as efficient electroactive channel materials for enhancement mode OECTs. [8] To date, however, essentially all reported OECTs have relied on hole transport (p-type), while the development of electron Organic electrochemical transistors (OECTs) have been the subject of intense research in recent years. To date, however, most of the reported OECTs rely entirely on p-type (hole transport) operation, while electron transporting (n-type) OECTs are rare. The combination of efficient and stable p-type and n-type OECTs would allow for the development of complementary circuits, dramatically advancing the sophistication of OECT-based technologies. Poor stability in air and aqueous electrolyte media, low electron mobility, and/or a lack of electrochemical reversibility, of available high-...

Doping of the reduced (undoped) PEDOT by oxygen during oxygen reduction reaction (ORR).

Electrocatalysis for energy‐efficient chemical transformations is a central concept behind sustainable technologies. Numerous efforts focus on synthesizing hydrogen peroxide, a major industrial chemical and potential fuel, using simple and green methods. Electrochemical synthesis of peroxide is a promising route. Herein it is demonstrated that the conducting polymer poly(3,4‐ethylenedioxythiophene), PEDOT, is an efficient and selective heterogeneous catalyst for the direct reduction of oxygen to hydrogen peroxide. While many metallic catalysts are known to generate peroxide, they subsequently catalyze decomposition of peroxide to water. PEDOT electrodes can support continuous generation of high concentrations of peroxide with Faraday efficiency remaining close to 100%. The mechanisms of PEDOT‐catalyzed reduction of O2 to H2O2 using in situ spectroscopic techniques and theoretical calculations, which both corroborate the existence of a chemisorbed reactive intermediate on the polymer chains that kinetically favors the selective reduction reaction to H2O2, are explored. These results offer a viable method for peroxide electrosynthesis and open new possibilities for intrinsic catalytic properties of conducting polymers.

Monitoring the cholesterol level is of great importance, especially for people with high risk of developing heart disease. Here we report on reagentless cholesterol detection in human plasma with a novel single-enzyme, membrane-free, self-powered biosensor, in which both cathodic and anodic bioelectrocatalytic reactions are powered by the same substrate. Cholesterol oxidase was immobilised in a sol-gel matrix on both the cathode and the anode. Hydrogen peroxide, a product of the enzymatic conversion of cholesterol, was electrocatalytically reduced, by the use of Prussian blue, at the cathode. In parallel, cholesterol oxidation catalysed by mediated cholesterol oxidase occurred at the anode. The analytical performance was assessed for both electrode systems separately. The combination of the two electrodes, formed on high surface-area carbon cloth electrodes, resulted in a self-powered biosensor with enhanced sensitivity (26.0 mA M -1 cm -2 ), compared to either of the two individual electrodes, and a dynamic range up to 4.1 mM cholesterol.Reagentless cholesterol detection with both electrochemical systems and with the self-powered biosensor was performed and the results were compared with the standard method of colorimetric cholesterol quantification.

SignificanceSpreading electrochemical technologies, such as energy, bioelectrochemical devices, and industrial electrochemical synthesis, require low-cost large area electrodes. Conducting polymers possess a unique combination of properties compared with most of the inorganic electrodes: acid resistance, the absence of surface-insulating oxide, low temperature and solution processability, a high natural abundance of their elements, molecular porosity. Conducting polymers are inhomogeneous conductors composed of ordered and disordered regions through which electronic transport takes place via percolation paths. We discovered that the density of percolation paths in the bulk of the material dictates the rate of electron transfer at the electrolyte–polymer electrode interface. This reveals one of the key parameters of designs to achieve efficient electrochemical technologies based on polymer electrodes.

We report on the novel protocol for enzyme immobilization into gel of siloxanes using water-organic mixtures with the high content of organic solvent as a reaction medium. Hydrolysis of alkoxysilanes carried out without excessive dilution with water resulted in more active and stable enzyme containing membranes. Immobilization of an inherently labile lactate oxidase according to the proposed sol-gel protocol over Prussian Blue modified electrode resulted in an advanced lactate biosensor characterized with a sensitivity of 0.18 A M(-1) cm(-2) in the flow injection analysis (FIA) mode over a wide dynamic range. A comparison with the known sensors has shown that analytical performances of the elaborated lactate biosensor are advantageous over both published systems and commercialized devices. The biosensor shows an appropriate stability and is suitable for clinical analysis (including noninvasive diagnostics) and food quality control.

Lactate (lactic acid) concentrations in sweat and venous and capillary blood of athletes were measured before and after exercise of the maximum aerobic power. Correlations between the increment of blood and sweat lactate concentrations were found. Lactate concentrations in the sweat can be used for evaluation of changes in blood lactate levels.

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