Ultrasensitive immunoassay for free prostate-specific antigen based on ferrocenecarboxylate enhanced cathodic electrochemiluminescence of peroxydisulfate

The catalytic effect of ferrocenecarboxylate (FCC; in the form of nanocrystals) on the cathodic electrochemiluminescence (ECL) of peroxodisulfate was studied and applied to an ECL immunoassay to quantify free prostate-specific antigen (fPSA). The nanocrystals were entrapped in graphene previously functionalized with poly(dimethyldiallylammonium chloride) to give a solid-state nanohybrid referred to as FCC-Gr-PDDA. When cast onto a glassy carbon electrode (GCE), the ECL of peroxodisulfate is strongly enhanced. An immunoelectrode was then constructed by coating the positively charged nanohybrids matrix of FCC-Gr-PDDA with negatively charged gold nanoparticles and then immobilizing antibody against fPSA on the Au-NPs. The resulting electrode is then incubated with samples containing fPSA. An immunocomplex is formed in the presence of fPSA, and this prevents the solid-state nanohybrid film to enhance the ECL of the peroxodisulfate luminophor. The observed decrease in ECL intensity is directly related to the concentration of fPSA antigen in the range from 0.005 to 5 ng mL−1, and the detection limit is as low as 1.7 pg mL−1. The method is deemed to provide a widely applicable and general platform for ECL-based immunoassays.