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

Abstract

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 aqueous 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.