Polydopamine nanospheres loaded with l-cysteine-coated cadmium sulfide quantum dots as photoelectrochemical signal amplifier for PSA detection

Highlights: • Electrochemically reduced graphene oxide-TiO₂ (ERGO-TiO₂) composite was prepared. • Quinone-rich polydopamine nanospheres (PDANS) was synthesized. • PDANS loaded with cadmium sulfide quantum dots was used as photocurrent signal label. • A photoelectrochemical sensor was constructed for detection of prostate specific antigen. -- Abstract: A sandwich-type photoelectrochemical (PEC) immunosensor was constructed for sensitive detection of prostate specific antigen (PSA). It was based on electrochemically reduced graphene oxide-TiO₂ (ERGO-TiO₂) as photoelectrochemical platform to immobilize capture antibody (Ab₁). Then, quinone-rich polydopamine nanospheres (PDANS) loaded detection antibody (Ab₂) and photocurrent signal label, l-cysteine-coated cadmium sulfide quantum dots (CdSQDs). ERGO-TiO₂ displayed greatly improved photocurrent response to white light. CdSQDs conjugated with PDANS further amplified photocurrent signal because of the good conductivity of PDANS and ERGO. The increased photocurrent showed a linear correlation with PSA in the concentration range from 0.02 pg mL⁻¹ to 200 ng mL⁻¹ with the detection limit of 6.8 fg mL⁻¹. It also revealed high selectivity and good stability.