The integration of n‐type (electron‐transporting) polymers with oxidase enzymes has allowed building high‐performance organic electrochemical transistor (OECT) based metabolite sensors. Yet, the operation mechanism of these devices is poorly understood. Here, the process is investigated for the conversion of metabolite oxidation to electrical current in an n‐type organic electrochemical transistor (n‐OECT). By monitoring oxygen (O2), hydrogen peroxide, and pH changes in the electrolyte as well as the potential of each electrical contact of the n‐OECT during glucose detection, light is shed on the physical phenomena occurring at the polymer‐enzyme interface. It is shown that the n‐type film performs O2 reduction reaction in its doped state and that the n‐OECT characteristics are sensitive to O2. A correlation is found between the consumption of electrolyte‐dissolved O2 and the generation of n‐OECT current during the metabolite oxidation. The results demonstrate how the sensitivity of a polymer to O2, species known to deteriorate the performance of many semiconductor devices, becomes a feature to exploit in sensor applications. The importance of in operando analysis of the electrolyte composition and the terminal potentials is highlighted for understanding the operation mechanism of bioelectronic devices and for sensor design and materials development.

Advancements in organic electrochemical transistor (OECT) applications have been largely driven by the development of organic electronic materials that allow for simultaneous ionic and electronic transport in the bulk of their films. These studies focus on achieving high steady-state OECT performance, governed by the electronic charge mobility and the capacitance of the polymer film in the channel, and an often underlooked property is the long-term operational stability. In this work, we present a strategy to improve the performance of p-type OECTs along with operational stability via two additives, i.e., a high-boiling-point solvent (chlorobenzene) and a Lewis acid (tris(pentafluoro phenyl)borane). Addition of a small amount of a cosolvent additive changes the arrangement of glycolated thiophene-based copolymer chains on the substrate toward a direction that allows for more efficient hole transport. The Lewis acid, on the other hand, boosts the OECT stability, mainly by preventing oxidative degradation. Using both additives in the solution grants OECTs with high operational stability and performance through changes in the film microstructure and the polymer's sensitivity to oxygen. This study highlights the use of additives as a means to enhance the OECT figure of merits without the need for new polymer synthesis.

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large-scale adaptation of these technologies and motivated researchers to look for alternative materials. [3] Organic electronic materials, such as graphene, [1,4] the small molecule perylenetetracarboxylic diimide, [5] or conjugated polymers like poly(3,4-ethylenedioxythiophene), PEDOT, [6] and poly(benzimidazobenzop henanthroline), BBL, [7] are potential ORR catalysts that can overcome the challenges laid by Pt. Among these materials, PEDOT exhibits high electrical conductivity, processability, transparency, flexibility, and biocompatibility. [8] Due to these properties, PEDOT is routinely used in a plethora of applications, including organic circuits, solar cells, batteries, capacitors, and biosensors, [8] and in some of these applications, the material has direct exposure to air and/or oxygen. PEDOT synthesis is versatile, relatively easy and proceeds at low temperatures, [8] while generating films with ORR rates competitive to Pt. [9] Along with the commercial availability of the EDOT monomer, its consistently decreasing price (60 USD kg −1 ) [6] promises for low-cost devices based on PEDOT. All these properties have rendered ORR conveyed by PEDOT a topic extensively investigated for metal-air batteries, [10] all-polymer batteries, [11] enzymatic fuel cells, [12] and H 2 O 2 synthesis. [6,9] PEDOT is also the workhorse material of organic bioelectronics, where polymer based electrodes or transistors are used at the interface with aqueous biological media to sense or stimulate biological events. [13] For these applications, however, ORR is unwanted as PEDOT derivatives were found to generate H 2 O 2 via path (I). [6,14] While H 2 O 2 is an important industrial chemical and generally considered as a green oxidant, [15] it is harmful to biological tissues, [16,17,18] and interferes with the stability of bioelectronic devices. [19] These concerns demand further exploration of PEDOT's catalytic properties and ORR pathways in physiological media, and whether it involves H 2 O 2 and under which conditions.Winther-Jensen et al. observed for the first time in 2008 that PEDOT synthesized by vapor phase polymerization catalyzed a reaction (II) based (four electrons) ORR. [20] However, it was later found that the film had iron (Fe(III)) oxide residues on the electrode, influencing the ORR activity and reaction path. [21] Nonetheless, research has since shown that standalone PEDOT without metal residues can also show ORR activity. [9,11] Additionally, a recent study found that for PEDOT films stabilized by the polyanion poly(sodium 4-styrenesulfonate), namely Oxygen reduction reaction (ORR) is a critical process for several electrocatalytic and photocatalytic devices. Poly(3,4-ethylenedioxythiophene), PEDOT, is an efficient ORR catalyst, with hydrogen peroxide (H 2 O 2 ) being the primary reaction product. Although H 2 O 2 is a green fuel for batteries and fuel cells and used as an industrial oxidant, it is toxic for living systems. As such, its production should be limited when PEDOT films are used in bioelectronic devi...

A simple and new fabrication method of Ag nanoparticle deposited "urchin-like" structures has been reported by the visible light-induced approach. The as-synthesized structures show the deposition of ∼5 nm sized Ag nanoparticles with nanogaps, which can generate highly enhanced electromagnetic fields for higher activity of surface-enhanced Raman scattering. Thus, these structures are important for highly sensitive Raman scattering activity.