A ternary CdS@Au-g-C₃N₄ heterojunction-based photoelectrochemical immunosensor for prostate specific antigen...

Photoactive materials with high photo-electron transfer efficiency and stable signal output hold a key role in constructing the photoelectrochemical (PEC) biosensing systems. In this study, the ternary CdS@Au-g-C₃N₄ heterojunction was first prepared and characterized, and its application in PEC bioanalysis was explored. The gold nanoparticles sandwiched between CdS and g-C₃N₄, acting as both plasmonic photosensitizer and electron relay, significantly boosted the light absorption and accelerated the charge transfer from g-C₃N₄ to CdS, both of which contributed to the enhancement of photoelectric conversion efficiency. Signal quenching with graphene oxide-CuS efficiently weakened the photocurrent from CdS@Au-g-C₃N₄. The combination of the excellent PEC properties of CdS@Au-g-C₃N₄ and the remarkable quenching effects of graphene oxide-CuS enabled construction of a sandwich-type PEC immunosensor for prostate specific antigen (PSA) detection. This immunosensor achieved sensitive PSA analysis by multiple signal amplification mechanisms, with a detection limit of 0.6 pg mL^-1 and a wide linear range from 1.0 pg mL^-1 to 10 ng mL^-1. This work not only demonstrates the great potential of noble metal sandwiched ternary heterojunctions in the PEC field, but also lays a foundation for developing the general PEC immunoassays.