Ultraviolet Fluorescent\nCarbon Nanodots as Sensors\nfor Hg<sup>2+</sup> Ions and Temperature

Ultraviolet-emitting\nfluorescent carbon dots (U-CDs)\nwere successfully\nsynthesized via a simple one-step hydrothermal method using benzene-1,3,5-tricarboxylic\nacid as the carbon source and <i>o</i>-phenylenediamine\n(OPD) as the nitrogen source. The U-CDs had an average particle size\nof 6.53 nm and were rich in functional groups such as amino, hydroxyl,\ncarboxyl, and carbonyl moieties. Their fluorescence excitation and\nemission wavelengths were observed at 325 and 365 nm, respectively,\nwith an impressive photoluminescence quantum yield of approximately\n20%. The U-CDs also exhibited excellent water solubility, salt resistance,\nand photobleaching resistance. By harnessing these unique properties,\na bifunctional fluorescent probe was developed to detect Hg<sup>2+</sup> concentration and temperature. The probe showed a strong linear\nresponse to Hg<sup>2+</sup> in the range of 0–42 μmol/L\nand to temperature between 30 and 60 °C, demonstrating high sensitivity\nand a low detection limit. These characteristics make the probe ideal\nfor analyzing real samples. This work not only expands the family\nof carbon dots but also introduces a simple and cost-effective method\nto synthesize multifunctional U-CDs, advancing their application in\ntemperature and metal ion sensors.