Gold nanoparticles/l-cysteine/graphene composite based immobilization strategy for an electrochemical immunosensor

A novel immobilization strategy combining gold nanoparticles (GNP) with graphene (Gr) via crosslinker L-cysteine (L-cys) for the enhancement of a HRP-labelled sandwiched electrochemical immunosensor was developed. In the fabrication process of the immobilization platform, graphene was first modified onto glassy carbon electrode (GCE), and then L-cys was electrodeposited onto the substrate of Gr for the following GNP assembling. The characteristics of the platform surface were studied by scanning electron microscopy (SEM), ultraviolet-visible (UV-vis) spectrometry, cyclic voltammetry (CV) and electrochemical alternating current impedance spectroscopy (EIS). From the SEM, interestingly we found the substrate of Gr induced the regular growth of L-cys, which may further improve the stable conjugation of GNP, which may result in more loading amount of the biomolecules. The special GNP/L-cys/Gr composite film constructed an effective antibody immobilization matrix and made the immunosensor hold high sensitivity, good stability and bioactivity. Under the optimized experimental conditions, a wide linear range of human IgG (HIgG) concentration from 0.2 to 320 ng mL−1 and a detection limit of 70 ng mL−1 were obtained. Accurate detection of HIgG in human serum samples was satisfyingly demonstrated by comparison to the standard ELISA assays.