Combining evident photocurrent of photoanode with signal amplification of biocathode: toward a sensitivity and specificity enhanced photoelectrochemical immunosensor

Highly sensitive and specific detection of biomarkers is of great importance for diagnosis and treatment of the related diseases or cancers. We herein developed a robust photoelectrochemical (PEC) immunosensor with enhanced sensitivity and specificity based on evident photocurrent output of the photoanode and significant signal amplification of the biocathode. Prostate specific antigen (PSA, Ag) was used as a target model to exhibit analytical performances of the designed PEC immunosensor. Two kinds of CuInS2 quantum dots (CIS QDs) with different composition were modified on the TiO2 nanotubes (TiO2-NTs) electrode to fabricate the photoanode. Due to the co-sensitization effect of the CIS QDs on TiO2-NTs, an evident photocurrent output was generated at the photoanode. For the biocathode, Au nanoparticles (AuNPs) and polydopamine (PDA) were modified in order on indium-tin oxide (ITO) electrode to immobilize capture PSA antibody (Ab(1)). Carboxyl-modified polystyrene (PS) nanospheres were coated with secondary antibodies (Ab(2)) to form PS@Ab(2) conjugates, which were used as signal amplifiers via the specific immunoreaction between Ag and Ab(2). Based on joint action of evident photocurrent output of the photoanode and significant signal amplification of the biocathode, the designed PEC immunosensor exhibited an ultralow detection limit of 3.4 fg/mL for target PSA detection. Meanwhile, it also showed an enhanced specificity owing to the separation of the photoanode and the biocathode.