Sandwich-type electrochemical immunosensor for sensitive determination of IgG based on the enhanced effects of poly-L-lysine functionalized reduced graphene oxide nanosheets and gold nanoparticles

Abstract

Poly-L-lysine functionalized reduced graphene oxide nanosheets (PLL-rGO) were prepared and thoroughly characterized with transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV/Vis, and FTIR spectra. PLL-rGO nanosheets were homogeneously mixed with IgG primary antibodies and were coated onto a glassy carbon electrode (GCE) surface. After being treated with glutaraldehyde vapor and subsequently blocked with bovine serum albumin, IgG antibodies were immobilized onto the PLL-rGO/GCE interface to fabricate an electrochemical immunosensing system. The as-fabricated immunosensor was characterized with voltammetry and electrochemical impedance spectroscopy. After specific binding with IgG, the immunosensor was incubated in a horseradish peroxidase labeled IgG secondary antibody solution. Based on the reduction current of the catalytic reaction towards H2O2, the experimental conditions for IgG determination were optimized. Under optimal conditions, the peak current variation was linearly related to IgG concentration in the range of 0.15 ~ 160.0 ng mL−1 with a detection limit of 0.087 ng mL−1 (S/N = 3). The practical applications of the immunosensor have also been demonstrated by determining IgG in clinical serum samples. The accuracy of the immunosensor was demonstrated by ELISA method and a recovery test.