WS2 nanosheets-sensitized CdS quantum dots heterostructure for photoelectrochemical immunoassay of alpha-fetoprotein coupled with enzyme-mediated biocatalytic precipitation

Based on enzymatic biocatalytic precipitation to quench the amplified photocurrent response generated from WS2 nanosheets-sensitized CdS quantum dots heterostructure, a novel photoelectrochemical immunosensor was constructed for sensitive alpha-fetoprotein (AFP) monitoring. The immunosensor comprised an anti-AFP antibody and a horseradish peroxidase-tagged anti-AFP antibody (HRP-Ab2), which served as a capture unit and a signal indicator, respectively. In the presence of AFP, HRP-Ab2 was immobilized on the electrode surface for establishing a sandwich-type immunocomplex via antigen–antibody interaction, and subsequently catalyzed 4-chloro-1-naphthol to form the nonconductive and insoluble precipitate. This precipitation effectively impeded the diffusion and electron transfer of the electron donor, thus achieving decreased photocurrent. Under optimized conditions, excellent linearity range (1 pg mL−1–20 ng mL−1), satisfactory detection limit (0.43 pg mL−1), desirable selectivity and good stability were obtained for the as-designed immunosensor. Moreover, the application of AFP determination in human serum allowed the immunosensor to hold great potential for early diagnostics of some cancer diseases.