Near-Infrared Electrochemiluminescence of Dual-Stabilizer-Capped Au Nanoclusters for Immunoassays

Surface engineering of electrochemiluminescence (ECL) emitters with capping agents is highly important, yet it remains a challenge. Herein, using N- acetyl-L-cysteine and cysteamine as model capping agents, a dual-stabilizer-capped strategy was proposed to achieve red-shifted ECL in the near-infrared region (NIR) via surface engineering water soluble and biocompatible Au nanoclusters (NCs). The dual-stabilizer-capped Au NCs were environment-friendly and exhibited efficient ECL emission at around 860 nm when utilizing triethanolamine as a coreactant, thus providing an NIR ECL tag for bioanalysis in aqueous medium. Benefiting from the low background of NIR emission and the good biocompatibility of the dual-stabilizer-capped Au NCs, a "signal on"-genre NIR ECL immunosensing method was obtained. Then, the immunosensor was established by using the carcinoembryonic antigen as a model analyte and the aforementioned Au NCs as a tag to label the signal antibody, which exhibited a broad linear range from 1 fg/mL to 0.5 ng/mL with a limit of detection of 0.33 fg /mL (S/N = 3). The work offers a method toward deepened understanding of the surface engineering of Au NCs with capping agents for tuning the ECL waveband and developing ECL systems in even longer wavebands.