Where Ions Meet Electrons: Advanced Bioelectronic Interfaces With Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) have evolved from passive electrodes into active transducers that sense, amplify, and increasingly compute at the boundary between circuits and living tissue. Over the past decade, advances span molecular design of organic mixed ionic-electronic conductors (OMIECs), electrolyte and channel engineering, device architectures, and circuit integration, to system-level translation. Unlike existing reviews that treat these in isolation, emphasizing single material classes, mechanisms, or applications, this article unifies them through bioelectronic interface design, working from biological demands to demonstrated capabilities. We analyze operating principles, benchmarking metrics and structure-property relationships across p-type, n-type, and biodegradable OMIECs. The electrolyte-channel region emerges as where biology and electronics converge; we survey gel electrolytes, semiconducting hydrogels, and all-gel devices, alongside planar, vertical, fiber, textile, and printed architectures. We assess how design choices impact performance across electrophysiological, biochemical, implantable, wearable, and plant-bioelectronic applications, while addressing biocompatibility, stability, and standardization requirements. Finally, we outline OECT-native platforms that consolidate sensing, memory, computation, and actuation within closed-loop, autonomous bioelectronic interfaces, arguing that this convergence represents the most consequential near-term direction for the field.