▎ 摘　　要

A one-step hydrothermal process to synthesize N-doping graphene quantum dots (N-GQDs) using PVP K90 as the novel self-passivation agent, in which the self-passivation and N-doping is realized simultaneously, is first proposed. The as-obtained N-GQDs with an average diameter of 1.9 +/- 0.6 nm can emit blue fluorescence (365 nm excitation), and possess a high fluorescent quantum yield (QY) of 64.2%. Due to the inner filter effect, N-GQDs are considered as outstanding fluorescent probes for detecting Cr(VI), which exhibit a lower detection limit (91 nM) and a wider linear range (0.1-100 mu M). Significantly, the fluorescent probe also indicates a remarkably high selectivity towards Cr(VI) among other metal ions with high concentrations. The fluorescence intensity of N-GQDs quenched by Cr(VI) is significantly turned on through adding reducing agent. What's more, N-GQDs have been successfully used to detect Cr(VI) in running water. In addition, the as-obtained N-GQDs could be further applied in cell imaging due to its biocompatibility and low cytotoxicity. Therefore, N-GQDs could be a wondrous sensing system for detecting Cr(VI) and fluorescent marker of MCF-7 cells with a wide range of potential applications. (C) 2019 Elsevier B.V. All rights reserved.