Multifunctional fluorescent carbon quantum dots for Zr4+ ion detection, pH response and cell imaging

In this paper, novel multifunctional nitrogen and sulfur co-doped fluorescent carbon quantum dots (Y-CDs) were prepared by a solvothermal method using o-phenylenediamine (OPD) as the carbon and nitrogen sources, L-Cysteine (L-Cys) as the sulfur source, and ethanol as the solvent. The prepared Y-CDs had high selectivity for the detection of Zirconium (Zr4+) with a detection limit of 68 nM due to the doping of S elements which formed electrical interactions with Zr4+ and thus caused aggregation fluorescence quenching. In addition, Y-CDs had excellent pH reversible response properties. The fluorescence of Y-CDs was almost completely quenched in the pH range of 1-5, and was restored when the pH returned to neutral or basic. Y-CDs also had good biocompatibility and low toxicity with the application of clear yellow fluorescence imaging in MCF-7 and EC cells. Yellow fluorescence Y-CDs focused mainly on the nucleus in MCF-7 cancer cells, while focused mainly on the cell membrane region in EC normal cells due to the different pH conditions of these two cells. The prepared Y-CDs would have promising applications in the fields of Zr4+ ion detection, pH response and cell imaging and cell identification.