Electrochemical sandwich immunoassay for insulin detection based on the use of gold nanoparticle-modified MoS nanosheets and the hybridization 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 MoS nanosheets decorated with gold nanoparticles (AuNPs) to immobilize a large amount of first antibody (Ab). Following exposure to insulin, secondary antibody (Ab) that was cross-linked to a DNA initiator strand (T) to form an Ab@T conjugate was added to undergo a sandwich immunoreaction. Subsequently, the long dsDNA concatemer was formed by a hybridization chain reaction between Ab@T and auxiliary probes (H, H). 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 0.1 pmol L to 1 nmol L insulin, and the detection limit is as low as 50 fmol L. The assay was acceptably specific, reproducible and stable. In our perception, it represents a viable new tool for determination of this important clinical parameter. Graphical abstract Schematic of a sandwich-type of electrochemical immunoassay for the determination of insulin based on the use of MoS nanosheets modified with gold nanoparticles (AuNP@MoS) and hybridization chain reaction (HCR).