In recent years, tremendous advances have been made in biosensors based on nanoscale electrochemical immunosensors for use in the fields of agriculture, food safety, biomedicine, quality control, and environmental and industrial monitoring.

This study describes a highly sensitive electrochemical immunosensor for the detection of human chorionic gonadotropin (hCG) that uses gold nanoparticles (AuNP) as the electrochemical label and graphene as electrode material. The primary antibody was first immobilized on the graphene working electrode surface by physical adsorption. Antigen hCG was then added and sandwiched with a secondary antibody labelled with AuNPs. After this, a series of sandwich-type immunoreactions were performed on the electrode, AuNPs were quantified by subjecting the immunocomplex to a preoxidation process of high potential at 1.2 V for 40 s and immediately reduced and scanned by differential pulse voltammtery (DPV). Electrodeposition of gold during the reduction stage of the redox reaction was determined by cyclic voltammetry (CV) that showed a linear relationship with the different hCG concentrations. In this study, a linear relationship between reduction peak current signals and hCG concentration from 0 to 500 pg mL⁻¹ (correlation coefficient of 0.97351) with a detection limit of 5 pg mL⁻¹ was obtained.