Selective detection of copper ion in complex real samples based on nitrogen-doped carbon quantum dots

Highly selective nitrogen-doped carbon quantum dots (ND-CQDs) for copper ion (Cu2+) determination were synthesized by a solvent-free pyrolysis of citric acid and histidine. The resultant ND-CQDs display a stable bright blue fluorescence with a satisfactory product yield of 56% and quantum yield of 16%. The ND-CQDs not only show good photostability under continuous UV irradiation, but are also dramatically stable against extreme ionic strengths. The solid powders of the ND-CQDs re-dispersed in water still maintain a strong blue fluorescence after storing at room temperature for 6 months. The ND-CQDs can be employed to selectively detect Cu2+ in a wide linear range of 0.6–30 μM. The detection limit is as low as 0.19 μM. The ND-CQDs were applied for Cu2+ detection in environmental water samples, fruit juice samples, and urine sample. Satisfactory recoveries of 96–102% with relative standard deviations below 3% were obtained. The research provided a promising prospect for selective detection of Cu2+ in the complex matrix.