N, S co-doped fluorescent carbon dots synthesized by microwave irradiation: a sensitive probe for Pb (II) ions detection in food samples

Sulfur and nitrogen co-doped carbon dots (NSCDs) were quickly synthesized by the microwave-assisted method from tri-ammonium citrate and thiourea. NSCDs showed a quantum yield of 11.5% with excitation and emission bands at 355 and 432 nm, respectively. Also, a fluorescence quenching was observed in the presence of Pb(II) ions, and the as-synthesized CDs were used as a sensitive probe for detecting Pb(II) in water and food samples. The results showed the optimal conditions for Pb(II) determination were CDs concentration of 0.02 mg mL(-1) at pH 6.0-7.0 and an incubation time of 20 min. The relative fluorescence intensity of NSCDs was proportional to Pb(II) concentrations in the range of 0.029-2.40 and 2.40-14.4 mu mol L-1 with a correlation coefficient (R-2) of 0.998 and 0.955, respectively, and a detection limit of 9.2 x 10(-3) mu mol L-1. Responses were highly repeatable, with a standard deviation below 3.5%. The suggested method demonstrates the potential of a green, fast, and low-cost approach for Pb(II) determination in water, tea, and rice samples with satisfying results.