Light‐Broadened Faradaic Regime of Organic Electrochemical Transistors for Accelerated Amperometric Biodetection

Faradaic‐mode organic electrochemical transistors (OECT) are promising but usually need hundreds of millivolts to sustain redox reactions. Decrease or even removal of the voltage penalty is highly desirable. Herein, the Faradic regime of the OECT is broadened toward zero bias by integrating a p‐n heterojunction of Cu 2 S‐diethylenetriamine (DETA)‐CdS for efficient photogating of poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonate) channel. Upon light illumination, it is found that an obvious Faradaic process is evolved at the gate/electrolyte interface under zero gate bias, suggesting the potential of sensitive amperometric biodetection with enhanced signal resolution. At the Cu 2 S‐DETA‐CdS/liquid interface, a biosensing process is introduced, combining with a DNA walker and enzymatic biocatalytic precipitation to produce a target‐dependent diffusion barrier, modulating the amperometric output with enhanced signal variations under light irradiation compared to that in the dark. The proposed system achieves the desired analytical performance for representative target miRNA‐10b with a low detection limit of 0.21 fM. This work features a light‐mediated OECT device with enhanced signal resolution and provides new operational paradigms and insights for novel optoelectronics interfacing with biological systems.