Electrochemical sandwich immunoassay for insulin detection based on the use of gold nanoparticle-modified MoS 2 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 MoS2 nanosheets decorated with gold nanoparticles (AuNPs) to immobilize a large amount of first antibody (Ab1 ). Following exposure to insulin, secondary antibody (Ab2 ) that was cross-linked to a DNA initiator strand (T0 ) to form an Ab2 @T0 conjugate was added to undergo a sandwich immunoreaction. Subsequently, the long dsDNA concatemer was formed by a hybridization chain reaction between Ab2 @T0 and auxiliary probes (H1 , H2 ). 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-1 to 1 nmol L-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. Graphical abstract Schematic of a sandwich-type of electrochemical immunoassay for the determination of insulin based on the use of MoS2 nanosheets modified with gold nanoparticles (AuNP@MoS2 ) and hybridization chain reaction (HCR).