Coreactant-Free Electrochemiluminescence from Gold–Silver Nanoclusters at Low Potential for Immunoassays

Low-potential and coreactant-free electrochemiluminescence (ECL) is a promising approach to eliminate exogenous influences from interfering substances and coreactants. Herein, by exploiting the prestored-electron nature of n-type nanoparticles, low-potential and coreactant-free ECL was developed using 4-amino-2-(methylthio)pyrimidine-5-carboxylic acid (AMPC)-capped AuAg nanoclusters, i.e., AMPC-AuAgNCs (AuAgNCs) as luminophores. AuAgNCs prestored with endogenous conduction band (CB) electrons can inject exogenous valence band (VB) holes around +0.80 V (vs Ag/AgCl) through an electrochemical oxidation process. The accumulated ECL spectral data demonstrate that these VB holes were captured by traps around the VB of AuAgNCs. Then the captured trap holes can directly recombine with the endogenous CB electrons. Thus, a distinct coreactant-free ECL process was generated around +0.80 V in the absence of any exogenous coreactants. Importantly, AuAgNCs were utilized as ECL tags to perform sandwich-type sensitive and selective immunoassays, which exhibited a wide linear response for determining human prostate-specific antigen (PSA) from 0.5 pg/mL to 1000 pg/mL and a limit of detection of 0.1 pg/mL (S/N = 3). This biosensor efficiently eliminated systematic errors and enhanced detection reliability without the involvement of exogenous coreactants. It displayed good assay performance for human serum samples, holding great promise in biomedical research.