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A novel sandwich-type electrochemical immunosensor was fabricated for the ultrasensitive electrochemical determination of prostate specific antigen (PSA) using silver-functionalized polyethyleneimine (PEI)-silica nanoparticles (NPs) (Ag + /PEI/SiO 2  NPs) as electrochemical labels. First, the immunosensor platform was prepared by covalently immobilizing capture antibodies on a poly diallyldimethyl ammonium chloride/carboxylated-gold nanoparticles (PDDA/AuNPs) modified glassy carbon electrode (GCE). After sandwich-type immunoreactions, the detection antibody was labeled by the amino-containing Ag + /PEI/SiO 2  NPs by strongly binding to carboxyl groups of protein. Next, many Ag +  with good complexing performance from each PEI/SiO 2  nanoparticles released after hydrofluoric acid (HF) in situ etching. Here, the AuNPs acted as a catalyst to reduce Ag +  into metallic Ag using PEI as the reducing agent. Accordingly, an extremely sharp voltammetric peak of electro-oxidized metallic Ag can be determined directly through differential pulse voltammetry (DPV) without metal pre-concentration, and had a close relationship with the concentrations of PSA antigen. Under the optimized conditions, the immunoassay exhibited good sensitivity and selectivity for the determination of PSA with a linear range from 0.01 to 10 pg·mL −1  and a detection limit of 3.5 fg·mL −1 . The new strategy provides a reliable, highly sensitive determination of the prostate cancer biomarker in biological samples with great potential for the fabrication of devices for clinical diagnostics.

analytical letters

Ultrasensitive Electrochemical Immunoassay for Prostate Specific Antigen (PSA) Based Upon Silver-Functionalized Polyethyleneimine (PEI)–Silica Nanoparticles (NPs)