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

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/SiO2 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/SiO2 NPs by strongly binding to carboxyl groups of protein. Next, many Ag+ with good complexing performance from each PEI/SiO2 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.