Hydrothermal fabrication of Zn/N co-doped carbon dots from glucose for highly selective fluorescent detection of Mg2+ in pharmaceutical, environmental and bioimaging applications.

The preparation of Zn/N-CDs aimed at solving the problems associated with their poor water solubility, low quantum yield, poor stability, and low fluorescence intensity. In this study, Zn/N co-doped CDs (Zn/N-CDs) were prepared by a simple one-pot hydrothermal synthesis, utilizing glucose, 2-aminopyridine, and zinc nitrate as precursors. It was observed that the prepared Zn/N-CDs showed bright blue fluorescence, good dispersibility in aqueous solutions, outstanding photostability, and particle uniformity, with an average size of 4.14 ± 0.81 nm (ranging from 1 to 7 nm). The maximum excitation wavelength and the emission wavelength were 300 nm and 405 nm, respectively, and the quantum yield was 24.2%. In addition, the fluorescence quenching of Zn/N-CDs in the presence of Mg2+ ions was attributed to the strong coordination effect between the Mg2+ ions and amino, hydroxyl, and carboxyl groups on the surface of the CDs. Moreover, Zn/N-CDs displayed a significant selectivity for Mg2+ ions among potential interfering metal ions, wide-ranging linearity in Mg2+ ion concentrations from 0 to 15 µM and a detection limit of 0.277 µM. Additional confirmation regarding the efficient interaction between Zn/N-CDs and Mg2+ ions was acquired by conducting fluorescence lifetime experiments. Moreover, the synthesized probe possessed high reversibility, repeatability, and stability. This probe was successfully applied for Mg2+ ion quantification in environmental, pharmaceutical, and biological samples. Since Zn/N-CDs possessed low cytotoxicity and were easily taken up by cells, the probe was applied for intracellular Mg2+ imaging in NIH-3T3 cell lines and HCT-116 cells.