Electrochemical immunosensor using nanotriplex of graphene quantum dots, Fe3O4, and Ag nanoparticles for tuberculosis

Abstract

A glassy carbon electrode (GCE) is modified with a nanotriplex [i.e., three nanolayers consisting of graphene quantum dot (GQD)-coated Fe3O4@Ag core-shell nanostructure (Fe3O4@Ag/GQD)]. The nanotriplex is a sensitive electrochemical biosensor platform for detecting Mycobacterium tuberculosis antigen (culture filtrate protein; CFP-10). Gold nanoparticles (AuNPs) conjugated to an anti-CFP-10 antibody are used as a label for signal amplification. The nanotriplex-based sensing platform attains synergetic electrochemical performance by the three different roles of three nanomaterials: Fe3O4 increases the surface to volume ratio; Ag enhances electrical conductivity; and GQD for loading more of the anti-CFP-10 antibody onto the electrode. The electron transfer kinetics at the surface of the electrode is simulated by means of the ButlereVolmer model. A sandwich-type immunoassay results by immobilizing the first antibody on the Fe3O4@Ag/GQD-modified GCE and by incubating this system with the antigen and then with AuNPs conjugated with the second anti-CFP-10 antibody (Ab(2)-AuNPs). The AuNPs are quantified by exposing the immunocomplex to a potential of 1.3V for 40s and scanning by differential pulse voltammetry. The immunosensor shows a wide linear range (0.005-500 mu g/mL) with a limit of detection (signal/noise = 3) reaching 0.33 ng/mL. The results suggest that the reliable and robust performance with high selectivity and simple operation may be extended to detection of other biomarkers of pathogenic bacteria. (C) 2018 Elsevier Ltd. All rights reserved.