Water-soluble, nitrogen-doped fluorescent carbon dots for highly sensitive and selective detection of Hg2+ in aqueous solution

Highly fluorescent water-soluble and nitrogen-doped carbon dots (NCDs) were synthesized by a simple one-pot hydrothermal method using citric acid as carbon source and urea as nitrogen source. Quantum yield of NCDs reaches 42.2%. As-obtained NCDs show a strong emission at 440 nm with an optimum excitation at 355 nm, and exhibit high photostability and excitation-independent photoluminescence (PL) behavior under excitation at 240-380 nm. However, such NCDs show excitation-dependent PL behavior under excitation of 380-480 nm. Because of the Hg2+-induced fluorescence quenching of carbon dots (CDs), such NCDs can be used as an effective fluorescent nanoprobe for highly selective and sensitive detection of Hg2+ in queous solution, with a limit of detection (LOD) as low as 2.91 nM in a linear range of 0-50 nM. The NCDs offer a rapid detection of Hg2+ with one-step rapid operation within 5 min. Further, as-prepared NCDs also exhibit high sensitivity towards Hg2+ in tap water and mineral water samples. The linear ranges of detection are both 0-50 nM. The LODs in tap water and mineral water samples are as low as 2.88 nM and 2.87 nM, respectively.