Construction of CdIn₂S₄/MXene‐TiO₂ Z‐Scheme Heterojunction for High‐Gain Organic Photoelectrochemical Transistor to Achieve Maximized Transconductance at Zero Bias

Abstract Interfacial charge‐carrier complexation is a bottleneck problem governing the gating effect of organic photoelectrochemical transistor (OPECT) biosensors. Therefore, it has long been desired to enhance the OPECT gating effect and realize the maximum transconductance at zero bias. In this study, an in situ engineered heterojunction gating and nano‐enzymatic catalytic integration of OPECT‐colorimetric dual‐mode sensing platform is developed for dibutyl phthalate detection. Specifically, highly efficient photoactive CdIn₂S₄/MXene‐TiO₂ Z‐scheme heterojunction is constructed by two‐step in situ engineering to promote effective separation of electron–hole pairs to achieve sensitive gating of poly(ethylene dioxythiophene):poly(styrene sulfonate)‐based OPECT. Target‐induced rolling circle amplification is used as the signal amplification unit, and Ag@Carbon Sphere (Ag─CS) is used as the signal conditioning element, which on the one hand causes shunting of photogenerated electrons, leading to energy transfer and reduced gating. At the same time, Ag─CS acts as a peroxidase‐mimicking nanozyme to oxidize the TMB discoloration. Importantly, the prepared sensor exhibits good selectivity and high sensitivity for the detection of dibutyl phthalate with a detection limit of 0.08 fM and also shows superior detection ability in real water bodies. Therefore, the sensor provides an ideal choice for toxic molecule detection and has a promising application in environmental monitoring and food analysis.