title: Fluorescent probes for "off-on" highly sensitive detection of Hg²⁺ and L-cysteine based on nitrogen-doped carbon dots.
abstract: Fluorescent nitrogen-doped carbon dots (NCDs) were synthesized by a facile, and low-cost one-step hydrothermal strategy using citric acid as carbon source and ammonia solution as nitrogen source for the first time. The obtained NCDs show stable blue fluorescence with a high quantum yield of 35.4%, along with the fluorescence lifetime of ca. 6.75 ns. Most importantly, Hg(2+) can completely quench the fluorescence of NCDs as a result of the formation of a non-fluorescent stable NCDs-Hg(2+) complex. Static fluorescence quenching towards Hg(2+) is proved by the Stern-Volmer equation, ultraviolet-visible absorption spectra, temperature dependent quenching and fluorescence lifetime measurements. Subsequently, the fluorescence of the NCDs-Hg(2+) system is completely recovered with the addition L-cysteine (L-Cys) owing to the dissociation of NCDs-Hg(2+) complex to form a more stable Hg(2+)-L-Cys complex by Hg(2+)-S bonding. Therefore, such NCDs can be used as an effective fluorescent "turn-off" probe for rapid, rather highly selective and sensitive detection of Hg(2+), with a limit of detection (LOD) as low as 1.48 nM and a linear detection range of 0-10 μM. Interestingly, NCDs-Hg(2+) system can be conveniently employed as a fluorescent "turn-on" sensor for highly selective and sensitive detection of L-Cys with a low LOD of 0.79 nM and a wide linear detection range of 0-50 μM. Further, the sensitivity of NCDs to Hg(2+) is preserved in tap water with a LOD of 1.65 nM and a linear detection range of 0-10 μM.
authors.affiliation: Key Laboratory of Interface Science and Engineering in Advanced Materials (Taiyuan University of Technology), Ministry of Education, Taiyuan 030024, China; College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, China; Department of Chemistry and Chemical Engineering, Lyuliang University, Lyuliang 033001, China; Research Center on Advanced Materials Science and Technology, Taiyuan University of Technology, Taiyuan 030024, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China.
authors.forename: Peipei
authors.initials: P
authors.lastname: Cui
authors.affiliation: Key Laboratory of Interface Science and Engineering in Advanced Materials (Taiyuan University of Technology), Ministry of Education, Taiyuan 030024, China; Research Center on Advanced Materials Science and Technology, Taiyuan University of Technology, Taiyuan 030024, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Interface Science and Engineering in Advanced Materials (Taiyuan University of Technology), Ministry of Education, Taiyuan 030024, China; College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, China.
authors.forename: Xiaoting
authors.initials: X
authors.lastname: Feng
authors.affiliation: Key Laboratory of Interface Science and Engineering in Advanced Materials (Taiyuan University of Technology), Ministry of Education, Taiyuan 030024, China; Research Center on Advanced Materials Science and Technology, Taiyuan University of Technology, Taiyuan 030024, China.
authors.forename: Yaling
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Key Laboratory of Interface Science and Engineering in Advanced Materials (Taiyuan University of Technology), Ministry of Education, Taiyuan 030024, China; Research Center on Advanced Materials Science and Technology, Taiyuan University of Technology, Taiyuan 030024, China. Electronic address: yyztyut@126.com.
authors.forename: Yongzhen
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Key Laboratory of Interface Science and Engineering in Advanced Materials (Taiyuan University of Technology), Ministry of Education, Taiyuan 030024, China; College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, China. Electronic address: liuxuguang@tyut.edu.cn.
authors.forename: Xuguang
authors.initials: X
authors.lastname: Liu
mesh_terms: D000641:Ammonia / Q000737:chemistry; D015374:Biosensing Techniques; D002244:Carbon / Q000737:chemistry*; D019343:Citric Acid / Q000737:chemistry; D003545:Cysteine / Q000032:analysis*; D060766:Drinking Water / Q000737:chemistry; D006801:Humans; D057230:Limit of Detection; D008628:Mercury / Q000032:analysis*; D009584:Nitrogen / Q000737:chemistry*; D045663:Quantum Dots / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D060766:Drinking Water; D019343:Citric Acid; D002244:Carbon; D000641:Ammonia; D008628:Mercury; D003545:Cysteine; D009584:Nitrogen
keywords: Fluorescence detection; Hg(2+); High selectivity; High sensitivity; L-Cys; Nitrogen-doped carbon dots