Flexible IGZO Field-Effect Transistor Biosensor Platform for Mechanically Stable and Cortisol Detection

Abstract

Flexible field-effect transistor (FET) biosensors based on amorphous oxide semiconductors are promising approaches for wearable biochemical monitoring. However, achieving electrical uniformity, mechanical stability, and receptor-mediated specificity simultaneously remains challenging. We report a wafer-scale fabricated indium–gallium–zinc oxide (IGZO) FET platform on a polyimide (PI) substrate for cortisol detection under liquid-gated operation. Statistical characterization across 50 devices demonstrates consistent transistor performance, with an average transconductance of 0.326 mS and an average subthreshold swing of 130.75 mV dec⁻¹. The devices maintain stable electrical performance under bending radii of 15–30 mm and after 100 deformation cycles. The bare IGZO FET exhibits reversible pH response, confirming stable electrostatic coupling at the semiconductor–electrolyte interface. Following covalent immobilization of a cortisol-specific aptamer, the device exhibits a concentration-dependent drain current response from 10 fM to 10 µm at a constant gate bias (V_G  =  0.4 V). The normalized response follows a linear relationship with a slope of 0.0195 per decade. Scrambled aptamer controls and non-target analytes confirm receptor-mediated specificity. These results demonstrate a flexible IGZO FET platform capable of translating cortisol binding into reproducible electrical signals, providing a mechanically robust and electrically stable biosensing platform for wearable biochemical monitoring.