▎ 摘　　要

Nitrogen and sulfur co-doped graphene oxide nanosheets (N,S-GO) were prepared via a facile one-step solvent-free approach using citric acid as a precursor and cysteine as a dopant. First, the graphene nucleus was formed via intermolecular dehydration of citric acid; N and S were then incorporated into the graphene structure by attacking the margin of the graphene nucleus. Crosslinking among the graphene nucleus via intermolecular condensation led to the final N,S-GO. The latter exhibited favorable photoluminescence behaviors, such as a high fluorescent quantum yield of 56.0%, excellent photoluminescence stability within the pH range 5-12, and high tolerance to external ionic strength 1.0 mol L-1 NaCl. The fluorescence energy transfer between AgNPs and N,S-GO could induce efficient quenching of N,S-GO fluorescence, and the presence of biothiols in the system restored fluorescence effectively, so a fluorescence off-on procedure was developed for quantitative detection of biothiols. Under optimal conditions, the limit of detection for cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) was 11.8, 4.9, and 7.3 nmol L-1, respectively. This sensing platform exhibited good selectivity toward biothiols in the presence of other amino acids. The practicability of this sensing platform was well demonstrated by determining biothiol content in human plasma samples, which revealed spiking recoveries of 97.10-101.50% with Cys.