Highly Selective and Sensitive Detection of Mercuric Ion Based on a Visual Fluorescence Method

The instant and on-site detection of trace aqueous mercuric ion still remains a challenge for environmental monitoring and protection. This work demonstrates a new analytical method and its utility for visual detection of aqueous He on the basis of a novel water-soluble CdSe-ZnS quantum dots (QDs) functionalized with a bidentate ligand of 2-hydroxyethyldithiocarbamate (HDTC). The fluorescence of the aqueous HDTC modified QDs (HDTC-QDs) could be selectively and efficiently quenched by Hg2+ through a surface chelating reaction between HDTC and Hg2+, and the detection limit was measured to be 1 ppb. Most interestingly, the orange fluorescence of the HDTC-QDs gradually changes to red upon the increasing amount of Hg2+ added besides the decreasing of the fluorescence intensity. By taking advantage of this optical phenomenon, a paper-based sensor for aqueous Hg2+ detection has been developed by immobilizing the HDTC-QDs on cellulose acetate paper which has low background fluorescence in the wavelength range. The paper-based sensor showed high sensitivity and selectivity for Hg2+ visual detection. When Hg2+ was dropped onto the paper-sensor, an obviously distinguishable fluorescence color evolution (from orange to red) could be clearly observed depending on the concentration of Hg2+. The limit of detection of the visual method for aqueous Hg2+ detection was as low as 0.2 ppm. The very simple and effective strategy reported here should facilitate the development of portable and reliable fluorescence chemosensors for mercuric pollution control.