Z-scheme I-BiOCl/CdS with abundant oxygen vacancies as highly effective cathodic material for photocathodic immunoassay.

A novel label-free photocathodic immunosensor was constructed by introducing a direct Z-scheme I-BiOCl/CdS cathodic material as highly effective photocatalyst for the selective detection of carcino embryonic antigen (CEA). The Z-scheme photocatalyst could promote the separation of photogenerated carriers and showed a more negative conduction band potential. In addition, the I-BiOCl with abundant oxygen vacancies could activate electron acceptors (i.e. O2 and H2O2) and made them reduce more completely, thus the sensitivity of the photocathodic immunosensor was significantly improved. Afterward, CEA antibody (Ab) was employed for the selective recognition of CEA target, which was covalently bonded to the substrate material. The formation of immune complexes hindered the diffusion of electron acceptors, thus the photocurrent decreased. Under the optimized conditions, the photocathodic immunosensor displayed abroad linear range (0.01-40.0 ng/mL) and a low detection limit (0.002 ng/mL) for CEA detection. Furthermore, acceptable reproducibility, excellent selectivity and high anti-interference ability were achieved. This work provides a new horizon for the design and development of Z-scheme cathodic materials as photoactive material for photocathodic biosensing.