Synthesis of lanthanum doped carbon dots for detection of mercury ion, multi-color imaging of cells and tissue, and bacteriostasis

This work describes a hydrothermal method for the preparation of multi-functional carbon quantum dots of the type La-CQDs. The La-CQDs are 4.3 ± 0.3 nm in diameter and have a good dispersion and exhibit excellent emission property and high stability, as well as excitation-dependent emission behavior with typical excitation/emission peaks at 350/460 nm. They can also be used as an effective fluorescent probe for the quenchometric determination of mercury ion in aqueous solution with a detection limit of 0.1 µM. The particles are readily internalized by liver epithelial HepG2 cells and enable multi-color fluorescence imaging by displaying green and red emission if excited with 488 and 543 nm light, respectively. Intravenous injection of the quantum dots in nude mice, in turn, enabled tissue imaging. The La-CQDs possess abundant phosphate, hydroxyl, pyridinic, pyridine-like and pyrrole-like nitrogen groups. Therefore, they can exhibit strong fluorescence, improve the accuracy as an optical monitoring code both in vitro and in vivo, and enhance blood compatibility. In vitro investigations show that La-CQDs do not exhibit significant apoptotic effects on NIH3T3 cells even at a high concentration (2.5 mg/mL) while they exhibit improved antibactericidal capacity of the La-CQDs against gram-positive S. aureus and gram-negative E. coli bacteria was also observed. No apparent pathological damages are observed in all organs during the 30-day period, which suggests that La-CQDs do not produce detectable long-term toxicological responses.