Ultraviolet Fluorescent Carbon Nanodots as Sensors for Hg²⁺ Ions and Temperature

Ultraviolet-emitting fluorescent carbon dots (U-CDs) were successfully synthesized via a simple one-step hydrothermal method using benzene-1,3,5-tricarboxylic acid as the carbon source and o-phenylenediamine (OPD) as the nitrogen source. The U-CDs had an average particle size of 6.53 nm and were rich in functional groups such as amino, hydroxyl, carboxyl, and carbonyl moieties. Their fluorescence excitation and emission wavelengths were observed at 325 and 365 nm, respectively, with an impressive photoluminescence quantum yield of approximately 20%. The U-CDs also exhibited excellent water solubility, salt resistance, and photobleaching resistance. By harnessing these unique properties, a bifunctional fluorescent probe was developed to detect Hg2+ concentration and temperature. The probe showed a strong linear response to Hg2+ in the range of 0–42 μmol/L and to temperature between 30 and 60 °C, demonstrating high sensitivity and a low detection limit. These characteristics make the probe ideal for analyzing real samples. This work not only expands the family of carbon dots but also introduces a simple and cost-effective method to synthesize multifunctional U-CDs, advancing their application in temperature and metal ion sensors.