Metal and heteroatoms co-doped fluorescent carbon dots for highly selective and sensitive detection of Mg ions in aqueous media: Applications in test strips, pharmaceutical, real samples and bioimaging.

In this study, we successfully synthesized fluorescent carbon dots (CDs) through a one-pot hydrothermal method, utilizing tartaric acid, cysteine, and nickel chloride as precursors. This approach allowed for the incorporation of metal ion (nickel) as well as nitrogen and sulfur heteroatoms into the carbon dot structure, resulting in nickel-doped, nitrogen, and sulfur-co-doped CDs (Ni/NS-CDs). A comprehensive characterization of the Ni/NS-CDs was conducted using FT-IR, XRD, Raman, XPS, and HR-TEM analysis confirmed the successful doping of nickel, nitrogen, and sulfur into the Ni/NS-CDs. HR-TEM analysis showed that the synthesized Ni/NS-CDs were spherical with a well-monodispersed average particle size of 2.1 ± 0.2 nm. The Ni/NS-CDs displayed strong fluorescence with excitation-dependent emission behavior and a high quantum yield of 23.60 %. When excited at 480 nm, the Ni/NS-CDs exhibited bright green emission at 524 nm, showcasing their excellent fluorescent characteristics. Additionally, the Ni/NS-CDs demonstrated remarkable stability across a broad pH range and high salt ionic strengths, further enhancing their practical applicability in diverse environments. The Ni/NS-CDs showed high sensitivity and selectivity towards Mg ions, with an impressively low limit of detection (LOD) of 19.38 nM within a wider range of 0-50 µM. Beyond sensing applications, the bright and stable fluorescence of the Ni/NS-CDs enabled clear cell imaging, making them promising candidates for use in biomedical research and diagnostics. Moreover, the practical utility of the Ni/NS-CDs were successfully applied for detecting Mg ions in environmental samples, illustrating their potential for ecological monitoring and water quality assessment. This broad applicability underscores the multifunctionality of the synthesized Ni/NS-CDs, positioning them as valuable nanomaterials in fields such as pharmaceuticals, bio-imaging, environmental science, and analytical chemistry.