Synthesis of sulfur-rich nitrogen dots from a single source precursor and its application in dual-mode sensing.

In this work, a strategy of sulfur-rich doped nitrogen dots (S-Ndots) based on a single-source precursor (SSP) was developed and applied to sensing of Hg. Fluorescent S-Ndots were synthesized by microwave-assisted method using 2-azidothiazole as a single-source precursor, which served as carbon, nitrogen and sulfur source simultaneously. This SSP approach guarantee efficient core doping and improve the effect of doping in a molecular level, which is more efficient and simpler than the doping strategy with multiple precursors. The results showed that the as-synthesized S-Ndots have high sulfur component up to 24.6%, and their specific structure effectively promoted artificial peroxidase activity and coordination interaction. Interestingly, the fluorescence intensity could be quenched obviously and the peroxidase activity of the S-Ndots were selectively inhibited by Hg, then the S-Ndots were applied to the dual-mode sensing of Hg with both fluorometric and colorimetric readout. The S-Ndots-based sensing assay with simplicity and rapidity showed high selectivity to Hg with the detection limit of 0.1 μmol/L by fluorescence spectroscopy and a distinguishable change in the color was observed by the naked eye. In addition, the accuracy and precision were evaluated based on the quantitative detection of Hg in industrial waste water samples with satisfactory results. Moreover, the S-Ndots with good biocompatibility were further explored for imaging of Hg in A549 cells. As a novel member of nitrogen quantum dots family, the S-Ndots hold great promise to broaden its applications in environmental and biological sensing.