<i>In Situ</i> Single Au@Cu₂O Core–Shell Nanoparticle Analysis-Enhanced Ultrasensitive Detection of Biothiols Using Light Scattering Imaging

Dark-field microscopy (DFM) as a single particle analysis (SPA) technique has been developed rapidly in recent years because of its high signal-to-noise ratio, enhanced sensitivity, and sufficient spatial and temporal resolution. Here, an <i>in situ</i> single Au@Cu₂O core-shell nanoparticle (Au@Cu₂O NP) light scattering imaging analysis was reported to realize the ultrasensitive detection of biothiols-cysteine (Cys) and glutathione (GSH). Based on the specific binding of Cu(I) with -SH to the formation of the Cu-S bond, it triggered the decomposition of the Cu₂O shell and exposure of the Au nanorods (Au NRs) in the presence of biothiols. Moreover, the process of Cu₂O shell dissolution has been observed in real time under DFM, which indicated that the scattering color changed from bright green to dark red and the scattering intensity decreased, correspondingly. Compared with <i>ex situ</i> SPA, <i>in situ</i> SPA exhibited significantly high sensitivity due to the effect of concentration polarization, which exhibited linear correlations over broad concentration ranges (Cys: 0.05-3 nM, GSH: 0.1-10 nM), with low detection limits of 15.52 pM (Cys) and 75.07 pM (GSH). Therefore, this work provides a smart strategy to find promising applications for the ultrasensitive detection of biomolecules through SPA.