Multifunctional N,S co-doped carbon quantum dots with pH- and thermo-dependent switchable fluorescent properties and highly selective detection of glutathione

Smart and multifunctional materials that can be responsive to the environment change have aroused extensive attention in the last few years, because they can be suitable for various applications, such as biosensing, biotechnology and drug delivery. Herein, multifunctional N,S co-doped carbon quantum dots (N,S-CQDs) with pH dependent and color-switchable fluorescent property were synthesized directly from L-cysteine and NH3·H2O by a one-step hydrothermal route at 100 °C. The N,S-CQDs are responsive to pH and exhibit color-switchable fluorescence performance between alkaline and acidic environments with good reversibility. The reasonable mechanism was also proposed. The N,S-CQDs exhibit well ionic stability, good biocompatibility and temperature sensitive fluorescent properties. In addition, the N,S-CQDs show a highly selective detection towards glutathione from other bithiols such as Cys and Hcy, which make the N,S-CQDs be sensor reagents for glutathione detection. Given these excellent performances, the as-synthesized N,S-CQDs have great potential to be used for pH sensor, temperature sensor and bioengineering applications in the near future.