Disposable Electrochemical Immunosensor by Using Carbon Sphere/Gold Nanoparticle Composites as Labels for Signal Amplification

This work designed a simple, sensitive, and low‐cost immunosensor for the detection of protein marker by using a carbon sphere/gold nanoparticle (CNS/AuNP) composite as an electrochemical label. The nanoscale carbon spheres, prepared with a hydrothermal method by using glucose as raw material, were used to load AuNPs for labeling antibody by electrostatic interaction, which provided a feasible pathway for electron transfer due to the remarkable conductivity. The disposable immunosensor was constructed by coating a polyethylene glycol (PEG) film on a screen‐printed carbon‐working electrode and then immobilizing capture antibody on the film. With a sandwich‐type immunoassay format, the analyte and then the CNS/AuNP‐labeled antibody were successively bound to the immunosensor. The bound AuNPs were finally electro‐oxidized in 0.1 M HCl to produce AuCl4− for differential pulse voltammetric (DPV) detection. The high‐loading capability of AuNPs on CNS for the sandwich‐type immunorecognition led to obvious signal amplification. By using human immunoglobulin G (IgG) as model target, the DPV signal of AuNPs after electro‐oxidized at optimal potential of +1.40 V for 40 s showed a wide linear dependence on the logarithm of target concentration ranging from 10 pg mL−1 to 10 ng mL−1. The detection limit was around 9 pg mL−1. The immunosensor showed excellent analytical performance with cost effectivity, good fabrication reproducibility, and acceptable precision and accuracy, providing significant potential application in clinical analysis. A convenient and low‐cost immunosensor was designed by using a polyethylene‐glycol‐film‐modified screen‐printed carbon electrode combined with a self‐synthesized carbon sphere/gold nanoparticle composite as an electrochemical label for signal amplification (see scheme). This efficient method provides a potential application for clinical detection of protein markers.