C-dots assisted synthesis of gold nanoparticles as labels to catalyze copper deposition for ultrasensitive electrochemical sensing of proteins

We report an ultrasensitive protocol for electrochemical sensing using the hydroxyl-rich C-dots assisted synthesis of gold nanoparticles (C-dots@AuNP) as labels with copper depositon reaction. The C-dots catalyzing copper deposition reaction was implemented for the first time. We constructed a sandwich-type immunosensor on the chitosan modified glassy carbon electrode (GCE) by glutaraldehyde (GA) crosslinking, with C-dots@AuNP as biolabels. Copper was deposited on the catalytic surfaces of second antibody-conjugated C-dots@AuNP nanoparticles through CuSO4-ascorbic acid reduction, because both C-dots and AuNPs could strongly catalyze the CuSO4 and ascorbic acid to form Cu particles, which amplified the detection signal. Then the corresponding antigen was quantified based on simultaneous chemical-dissolution/cathodic-preconcentration of copper for in-situ analysis using anodic stripping square wave voltammetry (ASSWV) directly on the modified electrode. Under optimized conditions, these electrodes were employed for sandwich-type immunoanalysis, pushing the lower limits of detection (LODs) down to the fg mL(-1) level for human immunoglobulin G (IgG) and cardiac troponin I (cTnI), a cardiac biomarker. These novel sensors have good stability and acceptable accuracy and reproducibility, suggesting potential applications in clinical diagnostics.