Built-In Electric Field-Assisted Enzyme Catalytic Amplification with ZnO/CIS Heterojunctions for Photoelectrochemical Immunoassay.

This study presents a ZnO/CdIn2S4 (ZnO/CIS) heterojunction-based photoelectrochemical immunosensor for sensitive prostate-specific antigen (PSA) detection. The separation and directional transport of photogenerated charge carriers are enhanced by the built-in electric field at the heterojunction interface, resulting in an increased initial photocurrent. Following immunocomplex formation, alkaline phosphatase-catalyzed ascorbic acid serves as an electron donor to quench photogenerated holes for signal amplification. Density functional theory (DFT) calculations and systematic electrochemical characterizations verify the critical role of the built-in electric field in enhancing charge separation and transfer. The sensor exhibited a wide linear range of 0.02-60 ng mL- 1, a low detection limit of 15.80 pg mL- 1, and great reproducibility and stability. This study provides mechanistic insights into heterojunction-assisted photoelectrochemical (PEC) sensing, establishing a practical strategy for high-performance clinical biosensors. The approach demonstrates scalability toward multifunctional PEC platforms for broader biomarker detection and comprehensive diagnostics.