Microwave-assisted one-pot synthesis of highly luminescent N-doped carbon dots for cellular imaging and multi-ion probing

The authors report on the microwave-assisted one-step synthesis of nitrogen-doped carbon dots (N-CDs) having a fluorescence quantum yield of 80% and a fluorescence lifetime of 15.0 ns. Citric acid and ethylenediamine were used as carbon source and as a nitrogen source, respectively. The N-CDs show excellent photostability over a wide range of pH values (4–11), even at high ion strength (2 M KCl) and after 4 h of continuous UV light irradiation. This makes these N-QDs promising candidates for fluorescent probes. Cellular toxicity test showed the N-CDs not to be cytotoxic to human nasopharyngeal carcinoma cells and human embryonic kidney cells even at 400 μg∙mL−1 levels after 48 h incubation. The fluorescence intensity of N-CDs at 445 nm is quenched by Fe(III), Hg(II), and chlorite ions, respectively. The N-CDs are shown to be viable fluorescent probes for the ions Fe(III), Hg(II), and chlorite. Respective detection limits are 12 nM, 0.8 nM, and 35 nM.