Near-Infrared Electrochemiluminescence of Gold Nanoclusters and Their Gene Assay Application with Thiol as the Bioconjugate Anchor

Amide bonds are most frequently utilized to form the bioconjugates of nanoclusters (NCs) and biomolecules; however, the amide bonds involved in the bioconjugation process tend to dramatically alter the functional group of NCs, decrease storage stability, and eventually block their practical bioapplication. With N-acetyl-l-cysteine (NAC)-capped AuNCs (NAC-AuNCs) as a model, we propose a biocompatible electrochemiluminescence (ECL) luminophore with thiol as a stabilizer and bioconjugate anchor. The NAC-AuNCs can exhibit a solely oxidative-reduction ECL process around +0.94 V with a maximum emission wavelength of around 824 nm. By immobilizing SH-modified probe hepatitis B virus (HBV) DNA (p-DNA) onto NAC-AuNCs via Au–S bonds, NAC-AuNCs can be used as ECL tags for gene assays with thiol as the anchor of bioconjugates, which provides an alternative to conventional bioconjugates and proves that ECL reagent kits can be developed in a 1-ethyl-3-(3-(dimethylamino)propyl) carbodiimide hydrochloride (EDC)-free way. The NIR ECL of NAC-AuNCs can be utilized to linearly determine HBV from 10 pM to 5 nM with a limit of detection (LOD) of 5 pM (S/N = 3). Notably, NAC-AuNCs can be safely stored for over four months without signal attenuation and can link the SH-modified gene without permanent precipitation.