Nitrogen fluoride co-doped carbon dots(NFCDs) were synthesized by hydrothermal method using citric acid,L-lysine and sodium fluoride as raw material.The structures of carbon dots were characterized by transmission electron microscopy(TEM),Fourier transform infrared spectroscopy(FT-IR),ultraviolet visible spectroscopy(UV-Vis) and fluorescence spectroscopy.Based on the fluorescence resonance energy transfer between riboflavin and NFCDs,a NFCDs fluorescent probe was constructed for the detection of riboflavin.Under the optimized experimental conditions,the detection linearity of this method for riboflavin ranged from 3.0 μmol/L to 66.5 μmol/L with a detection limit of 0.26 μmol/L,calculated by 3 times of the signal-to-noise ratio.The probe was successfully applied to the determination of riboflavin in milk and milk powder with recoveries of 96.7%-103%.In addition,the low toxicity of NFCDs on HeLa cells was determined by the MTT assay,and they were also applied to fluorescence imaging of cells,and the presence of riboflavin in cells was successfully confirmed by laser scanning confocal microscopy.