Fast and High-Transconductance Organic Electrochemical Transistor for Implantable Peripheral Nerve Recording System

Organic bioelectronics is an emerging field that leverages the unique properties of organic semiconductors in interfacing with cells, tissues, and biological systems. Organic electrochemical transistors (OECTs), in particular, are promising for wearable and implantable electronics due to their low operating voltage, high transconductance, stability in aqueous environments, and biocompatibility. The operation of OECTs is characterized by ion penetrating into the polymer channel for electrochemical doping/dedoping through applying gate voltage bias. However, OECTs face a significant challenge due to an inherent trade-off between transconductance (gm, defined as ∂I_D/∂V_G) and transient characteristics, which limits their range of sensing applications. In our study, we addressed this issue by modifying the channel structure to micro/nano structure using conventional lithography and reactive ion etching process. We hypothesized that the introduction of micro/nano structures into the channel architectures will allow more efficient ionic penetration from electrolytes to all sides of the channel, significantly increases the surface-to-volume ratio, thereby reducing the effective path of ions. The transient response of the micro/nano structured channel OECT showed that as the size of the patterned structure decreases, the effective path of ions for doping/dedoping process is reduced, and consequently enhance the operation speed of OECT. We also controlled the OECT channel structure precisely and uniformly, which makes it highly scalable for various application. Our results show that micro/nano structured channel OECTs achieve improved response times compared to conventional structures maintaining high transconductance about 10 mS. Subsequently, we developed our micro/nano structured channel OECT arrays as an implantable nerve cuff for monitoring peripheral nerve signal. This array was utilized to be wrapped around the peripheral nerve of the anesthetized rat to monitor neural signals induced by external mechanical stimulation. We envision that these results will provide valuable insights for kinetics of OECTs operation and the fields of neuroprosthetics and neurological diseases.