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. Graphical abstract Schematic of the microwave-assisted one-pot synthesis of highly luminescent N-doped carbon dots (N-CDs) by using citric acid (CA) and ethylenediamine (EDA) as carbon and nitrogen sources. The N-CDs were applied to multi-ion [Fe(III); Hg(II) and chlorite] probing and to imaging of human nasopharyngeal carcinoma cells (upper panel) and human embryonic kidney cells (lower panel).