Target-Induced Chemical Reaction Modulated Optical Fiber-Gated Organic Photoelectrochemical Transistor for <i>in Vivo</i> H₂S Detection

Real time detection of hydrogen sulfide (H₂S) in deep brain regions is of great significance. Photoelectrochemical (PEC) biosensors hold promise for real-time monitoring but low sensitivity due to the use of small electrode restrained its application. In this study, a miniaturized sensor that integrates organic photoelectrochemical transistors (OPECTs) with optical fiber (OF) microelectrodes was designed for the first time, which can amplify the small PEC signal into large channel current change. A conductive gold layer and cuprous oxide nanoparticles (Cu₂O NPs) were sequentially deposited onto the OF, followed by a Nafion polymer coating to enhance anti-interference capabilities. Cu₂O reacts with H₂S to generate Cu₂S. The resulting Cu₂O/Cu₂S heterojunction induces changes in the PEC signal and channel current. Compared to a conventional PEC system, the OPECT sensor has higher sensitivity and lower detection limit, enabling monitoring of H₂S concentration fluctuations within the rat brain, which demonstrates the approach's capability for highly sensitive <i>in vivo</i> biomarker detection.