Dual-Mode Electrochemical Immunoassay for Insulin Based on Cu7S4-Au as a Double Signal Indicator.

Abstract

The detection of insulin by electrochemical (EC) immunoassay is desirable but highly challenged due to the obstacle of improving its accuracy, especially in a single-response system. In this work, based on Cu7S4-Au as a dual signal indicator, we fabricated a dual-mode electrochemical immunoassay for insulin. Especially, Cu7S4 presents a strong differential pulse voltammetry (DPV) signal for the electron transfer between Cu2+ and Cu+, without the addition of K3[Fe(CN)6] or other electron transfer mediators. Furthermore, Cu7S4 displays high sensitivity and high electrocatalytic activity toward the reduction of H2O2 through chronoamperometry (CA). The introduction of Au nanoparticles can not only link on the surface of Cu7S4 by the chemical bond of Au-SH, but also connect the second antibody (Ab2) by the chemical bond of Au-N. Due to the superior electroconductivity of Au nanoparticles and the synergistic effect between the Au nanoparticles and Cu7S4, a high sensitivity is achieved by means of DPV and CA. To improve the loading capacity of antibodies, nanofiber polyaniline covalently grafted graphene (GS-PANI) linked with Au nanoparticles (GS-PANI-Au) as the matrix material was prepared. Based on Cu7S4-Au as a double signal indicator, the developed EC immunoassay for insulin exhibits a wide linear response for insulin detection in the range from 0.1 pg/mL to 50 ng/mL, with a low detection limit of 35.8 and 12.4 fg/mL through DPV and CA modes, respectively. Furthermore, the immunosensor displays an excellent analytical capability for insulin and promises application in quantitative detection of other disease markers in clinical diagnosis.