Fluorescent carbon dots synthesized by microwave-assisted pyrolysis for chromium(VI) and ascorbic acid sensing and logic gate operation.

Herein, nitrogen, sulfur co-doped fluorescent carbon dots (N,SCDs) were synthesized by simple and facile microwave-assisted pyrolysis using ammonium citrate and cysteamine hydrochloride as precursors. The obtained N,SCDs exhibited outstanding photostability, excitation-wavelength independence, excellent fluorescence properties with fluorescence quantum yield (FLQY) up to 54.8%. Significantly, the fluorescence of N,SCDs was effectively quenched by Cr(VI) based on inner filter effect (IFE). Subsequently, the fluorescence of the N,SCDs-Cr(VI) system successfully recovered with addition of ascorbic acid (AA) owing to redox reaction between Cr(VI) and AA. Therefore, N,SCDs could be employed as an efficient fluorescent "turn-off" probe for highly sensitive detection of Cr(VI), with a liner detection range from 0.35 to 126.0 μmol L-1 and a detection limit of 0.11 μmol L-1 . Meanwhile, the N,SCDs-Cr(VI) system could be used as an fluorescent "turn-on" sensor for detection of AA with a detection limit of 0.17 μmol L-1 and a liner detection range of 0.57-264.0 μmol L-1 . Interestingly, a molecular logic gate was constructed based on the fluorescence recover of the N,SCDs-Cr(VI) system in the presence of AA. Most importantly, this fluorescent probe has been applied for determination of Cr(VI) and AA in environmental and biological fields with satisfactory results.