A kind of nitrogen doped carbon quantum dots(N-CQDs)

with economy

low toxicity and even strong fluorescence performance

were successfully synthesized by hydrothermal method using L citrulline and urea as precursors.The performance of N-CQDs was characterized by transmission electron microscopy(TEM)

Fourier transform infrared spectroscopy(FT-IR) and X-ray photoelectron spectroscopy(XPS)

etc.Results showed that the quantum yield of the N-CQDs reached up to 39.2% with an average particle size of 2.8 nm

which could be used for HepG2 cell imaging in view of their good water solubility

stability and biocompatibility.In addition

a fluorescence probe with high selectivity and sensitivity was proposed for the detection of o-nitrophenol(o-NP) based on an experimental phenomenon that the fluorescence of the CQDs could be specifically quenched by o-NP.Results showed that there was a good linear relationship for o-NP in the range of 0.083 3-12.0 μmol/L with a correlation coefficient(r2) of 0.998 and a detection limit(LOD) of 25.2 nmol/L(S/N=3).The proposed method was successfully applied in the detection of o-NP in real water samples from Wanfeng Lake and Dingxiao River in Guizhou province.