Nanozymes induced Z-scheme Mn-BiVO4/Au/Bi2S3 heterostructure photoelectrochemical signal amplification for CA72-4 detection.

A photoelectrochemical (PEC) immunosensor was developed for the ultrasensitive detection of the gastric cancer biomarker CA72-4, employing a Z-scheme Mn-BiVO4/Au/Bi2S3 heterojunction in synergy with Fe3O4@Pt nanozymes. To assess the influence of heterojunction configuration on PEC performance, a comparative investigation was carried out by modulating the deposition sites of gold nanoparticles (Au NPs), resulting in the formation of two distinct Z-scheme Mn-BiVO4/Au/Bi2S3 (MBAB) and Type-II Mn-BiVO4/Bi2S3/Au (MBBA) heterostructures. The results revealed that the proposed Z-scheme configuration demonstrated significantly enhanced charge separation efficiency and a notably amplified photocurrent response compared to the proposed Type-II configuration. Moreover, under anodic bias, the photoinduced holes in BiVO4 facilitated water oxidation, leading to the generation of hydrogen peroxide (H2O2), which further promoted charge separation and contributed to an increased photocurrent. To further amplify the PEC signal, Fe3O4@Pt nanozymes, possessing robust peroxidase-like catalytic activity and excellent stability, were incorporated as signal amplifiers. These nanozymes efficiently decomposed H2O2 produced by hole-mediated water oxidation, thereby improving charge carrier separation and transport, thereby significantly improving sensor sensitivity. Thanks to the synergy between the optimized Z-scheme heterojunction and nanozyme-mediated signal amplification, the proposed PEC immunosensor exhibited a wide linear detection range of 0.001-100 U/mL and an exceptionally low detection limit of 0.0004 U/mL. This work presented an innovative and highly efficient PEC sensing strategy for the sensitive detection of CA72-4, offering promising potential for clinical diagnostic applications.