Polydopamine nanospheres with multiple quenching effect on TiO/CdS:Mn for highly sensitive photoelectrochemical assay of tumor markers.

A photoelectrochemical (PEC) immunosensing strategy based on the multiple quenching of polydopamine nanoparticles (PDA NPs) to Mn-doped CdS-modified TiO nanoparticles (TiO/CdS:Mn) was designed for the highly sensitive detection of carcinoembryonic antigen (CEA). The uniform PDA NPs possessed good dispersibility, good biocompatibility, and abundant functional groups for biomolecule assembly. They also had unique photophysical properties, with light absorption spanning the visible to infrared light range. When the immune-recognition brought the PDA NPs close to the TiO/CdS:Mn interface, the PDA NPs competed with TiO/CdS:Mn to absorb light, consumed photoelectrons generated in the TiO/CdS:Mn, and hindered the access of electron donors to photoactive materials. The contribution from these aspects thus led to a significant decrease in photocurrent. Benefiting from the multiple quenching mechanism, the PEC immunosensor showed high sensitivity for CEA detection. Under optimal conditions, a low detection limit of 0.02 pg/mL and a wide linear relationship from 0.1 pg/mL to 100 ng/mL were obtained. The immunoassay showed good reproducibility and stability, and good selectivity and high accuracy in serum sample analysis. In this regard, PEC immunosensors may have great application potential for screening tumor markers and the prevention and monitoring of serious diseases.