▎ 摘　　要

In this work, nitrogen and sulfur co-doped graphene quantum dots (N,S-GQDs), exhibiting bright blue fluorescence with an excellent quantum yield of 67%, were facilely prepared by one-pot pyrolysis of citric acid (carbon source) and cysteine (N and S sources). Compared to conventional GQDs, the doping of nitrogen/sulfur had significantly altered and uniformed the surface state, and the as-obtained N,S-GQDs displayed an excitation-independent emission behavior, where the fluorescence decay curve was nearly a single exponential. On the basis of the well-known inner filter effect of silver nanoparticles (AgNPs) and cyanide (CN-)-induced etching of AgNPs, the fluorescence of N,S-GQDs could be quenched by AgNPs, and the nonfluorescence state of the as-prepared N,S-GQD-AgNP ensemble would be switched on in the presence of CN-. Meanwhile, the addition of N,S-GQDs has almost ignorable effect on the absorption spectrum of the AgNP solution, however, the subsequent introduction of CN- would significantly decrease the absorbance value owing to the aforementioned etching behavior of CN-. Therefore, a N,S-GQD-based fluorescent and AgNP-related colorimetric dual-mode analytical system for efficacious determination of CN- has been rationally designed and successfully developed for the first time. Furthermore, the detection limits were found to be 0.52 mu M and 0.78 mu M for fluorescent and calorimetric sensors individually under the optimal experiment conditions. The proposed N,S-GQD-AgNP-based assay can be successfully utilized to the quantitative determination of CN- in spiked tap water samples. (C) 2016 Published by Elsevier B.V.