Electrochemical sandwich immunoassay for insulin detection based on the use of gold nanoparticle-modifiedMoS2 nanosheets and thehybridization chain reaction

A sandwich-type of electrochemical immunoassay is described for the determination of insulin. It is based on the use of a glassy carbon electrode that was modified with MoS2 nanosheets decorated with gold nanoparticles (AuNPs) to immobilize a large amount of first antibody (Ab(1)). Following exposure to insulin, secondary antibody (Ab(2)) that was cross-linked to a DNA initiator strand (T-0) to form an Ab(2)@T-0 conjugate was added to undergo a sandwich immunoreaction. Subsequently, the long dsDNA concatemer was formed by a hybridization chain reaction between Ab(2)@T-0 and auxiliary probes (H-1, H-2). Finally, the electrochemical probe ruthenium(II) hexaammine was intercalated into the dsHCR products via electrostatic interaction between the anionic DNA phosphate backbones and the cationic probe. The electrochemical response, best measured at a potential of around-0.21 V (vs Ag/AgCl) has a dynamic range that extends from 0.1pmolL(-1) to 1nmolL(-1) insulin, and the detection limit is as low as 50 fmol L-1. The assay was acceptably specific, reproducible and stable. In our perception, it represents a viable new tool for determination of this important clinical parameter.