Ag(I)-cysteamine complex based electrochemical stripping immunoassay: ultrasensitive human IgG detection

An ultrasensitive electrochemical immunosensor for a protein using a Ag (I)-cysteamine complex (Ag-Cys) as a label was fabricated. The low detection of a protein was based on the electrochemical stripping of Ag from the adsorbed Ag-Cys complex on the gold nanoparticles (AuNPs) conjugated human immunoglobulin G (anti-IgG) antibody (AuNPs-anti-IgG). The electrochemical immunosensor was fabricated by immobilizing anti-IgG antibody on a poly-5,2':5',2''-terthiophene-3'-carboxylic acid (polyTTCA) film grown on the glassy carbon electrode through the covalent bond formation between amine groups of anti-IgG and carboxylic acid groups of polyTTCA. The target protein, IgG was sandwiched between the anti-IgG antibody that covalently attached onto the polyTTCA layer and AuNPs-anti-IgG. Using square wave voltammetry, well defined Ag stripping voltammograms were obtained for the each target concentration. Various experimental parameters were optimized and interference effects from other proteins were checked out. The immunosensor exhibited a wide dynamic range with the detection limit of 0.4 ± 0.05 fg/mL. To evaluate the analytical reliability, the proposed immunosensor was applied to human IgG spiked serum samples and acceptable results were obtained indicating that the method can be readily extended to other bioaffinity assays of clinical or environmental significance.