Nitrogen-doped carbon dots as a highly selective and sensitive fluorescent probe for sensing Mg²⁺ ions in aqueous solution, and their application in the detection and imaging of intracellular Mg²⁺ ions

The magnesium (Mg²⁺) ion is the second most abundant intracellular cation after potassium, and it is involved in a variety of biological processes and physiological functions. Because of the different effects which are dependent on Mg²⁺ ion concentration, it is critical to monitor Mg²⁺ ion levels in biological systems. Here, we report the hydrothermal synthesis of photoluminescent N-doped carbon dots (NCDs) using 4-Hydroxybenzaldehyde and 1, 2, 4, 5-benzenetetramine tetrahydrochloride as carbon and nitrogen sources, respectively. The as-synthesized NCDs demonstrated excitation dependent photoluminescence (PL) with a quantum yield of 16.2%. Because of water dispersibility and chelating functional groups, NCDs were used for highly selective detection of Mg²⁺ ions using ratiometric PL enhancement with a detection limit of 60 μM. Following that, based on highly biocompatibility and sensing of Mg²⁺ ions in aqueous solutions, NCDs were employed as photoluminescent probe to detect the Mg²⁺ ions of mammalian cell lines such as J774, HeLa, and Hek293T, which is most likely due to effective complex formation between NCDs and the intracellular Mg²⁺ ions. As far as we could possibly know, this is the first report of aqueous solution dispersed carbon dots for intracellular sensing and imaging of Mg²⁺ ions based solely on an increase in NCDs PL intensity.