Sensitive Bioanalysis Based on in-Situ Droplet Anodic Stripping Voltammetric Detection of CdS Quantum Dots Label after Enhanced Cathodic Preconcentration

We report a protocol of CdS-labeled sandwich-type amperometric bioanalysis with high sensitivity, on the basis of simultaneous chemical-dissolution/cathodic-enrichment of the CdS quantum dot biolabel and anodic stripping voltammetry (ASV) detection of Cd directly on the bioelectrode. We added a microliter droplet of 0.1 M aqueous HNO(3) to dissolve CdS on the bioelectrode and simultaneously achieved the potentiostatic cathodic preconcentration of Cd by starting the potentiostatic operation before HNO(3) addition, which can largely increase the ASV signal. Our protocol was used for immunoanalysis and aptamer-based bioanalysis of several proteins, giving limits of detection of 4.5 fg·mL(−1) for human immunoglobulin G, 3.0 fg·mL(−1) for human carcinoembryonic antigen (CEA), 4.9 fg·mL(−1) for human α-fetoprotein (AFP), and 0.9 fM for thrombin, which are better than many reported results. The simultaneous and sensitive analysis of CEA and AFP at two screen-printed carbon electrodes was also conducted by our protocol.