Green synthesis and multifunctional applications of nitrogen-doped carbon quantum dots via one-step hydrothermal carbonization of Curcuma zedoaria.

Low-dimensional (<10 nm) semiconductor carbon quantum dots (CQDs) have been widely used in metal ion sensing and bioimaging. Here, we used the renewable resource Curcuma zedoaria as a carbon source and prepared green carbon quantum dots with good water solubility by a hydrothermal method without any chemical reagent. At different pH values (4-6) and high NaCl concentrations, the photoluminescence of the CQDs was very stable, which indicated that they were suitable for a wide range of applications even under harsh conditions. The CQDs exhibited fluorescence quenching in the presence of Fe ions, indicating their application potential as fluorescence probes for the sensitive and selective detection of Fe ions. The CQDs showed high photostability, low cytotoxicity, and good hemolytic activity, and were successfully applied to bioimaging experiments, i.e. multicolor cell imaging in L-02 (human normal hepatocytes) and CHL (Chinese hamster lung) cells with and without Fe, as well as wash-free labeling imaging of Staphylococcus aureus and Escherichia coli. The CQDs also showed good free radical scavenging activity and demonstrated a protective effect against photooxidative damage to L-02 cells. These results indicate that CQDs obtained from medicinal herb sources have multiple potential applications in the fields of sensing, bioimaging, and even disease diagnosis.