Introducing Interface Redox Processes in Faradaic Floating Gate Organic Electrochemical Sensors to Improve Sensor Function in Complex Environments

Organic electrochemical transistors (OECTs) have attracted significant interest in cutting-edge sensing and bioelectronics. One fundamental approach to amplify signals and improve the performance of the OECT sensing is the use of redox reactions at gate electrodes and/or polymer channels. Faradaic processes increase the electric field drop at the semiconductor channel, which can promote an increased transconductance. However, many biological analytes, including peptides and proteins, are not redox-active and are not immediately amenable to Faradaic OECT biosensing. Herein, we establish a set of systematic redox interface modifications to floating gate (FG) OECTs to enable significantly greater transduction at lower operating voltages over capacitive gating in FG architectures. The proof-of-concept device platform consists of (1) a second FG that operates using mixed monolayers of redox-active species and a selective binding probe and (2) a solid-state OECT element with a redox mediator in an ion gel as the electrolyte to align the energy level for efficient doping and amplification. As a point of validation, a Faradaic electrochemical immunoassay for neuropeptide Y (NPY) is used; the NPY immunoassay is composed of ternary monolayers of redox labels and biorecognition elements, with a 439 pM detection of NPY in artificial sweat. Overall, we successfully demonstrate a power-saving Faradaic FG OECT device in the solid state, which is compatible with easy miniaturization and suitable for printable/wearable sensors and bioelectronics for various applications, from point-of-care diagnostics to healthcare.