| The heavy metal ion contamination has attracted peoples extensive attention because of their toxicity.In recent years, poisoning because people wrongly eat substances which contain heavy metal ions was commonly occurred,so the detection of heavy metal ions is particularly important. Because of their superior fluorescence, quantum dots(QDs) played an important role in the detection of heavy metal ions. However, the detection of heavy metal ions is primarily by changing the ligands on the surface of the QDs to detect different metal ions. The size-dependently optical and physical properties of semiconductor QDs had been well documented, but their effects on sensing performance were rarely investigated. In addition, the water often contains a variety of metal ions, therefore, to realize the simultaneously detection of two or more metal ions is rather significant.This study is mainly to study the impact of the particle size of the QDs for the detection of metal ions. First, homocysteine, L-cysteine and mercapto acid capped CdTe QDs were synthesized under the same conditions to obtion different sizes of CdTe QDs. The QDs were characterized by fluorescence spectroscopy, while the new ligands homocysteine modified CdTe quantum dots were XRD characterization. Before the metal ions detected, we invested the PH value, buffer concentration and the concentration of quantum dots which impacted on it. Then the different sizes of QDs were used for detecting the common metal ions. We found that the small QDs are quenched by Hg2+,with the particle increasing, the QDs becomes not obvious to Hg2+,while become more and more sensitive to Ag+. The experiments confirmed that the QDs had a significant size effect in the detection of heavy metal ions. Meanwhile, the large size of homocysteine capped CdTe quantum dots for Ag+detection limits is as low as8.3nM, lower than ever before on the Ag+lower detection limits. While taking advantage of the standard addition method for pond water and lake water testing, we found that the test results consistent with Ag+concentration added, proveing the Ag+existence in the pond water and lake water and can also be achieved by this method. Under different conditions,the two size of mercapto acid capped CdTe QDs which had green fluorescence and red fluorescence were synthesized and the Two kinds of QDs were quenched for Hg2+and Ag+,respectively. After mixing the two QDs, the mixed QDs showing yellow fluorescent under UV light irradiation. With the increasing of Hg2+concentration, the fluorescence color of the mixing QDs was gradually from yellow to red, and the fluorescence color of the mixing QDs was from yellow to green when Ag+concentration was increasing. Using this method, We realized the Hg2+and Ag+fast, sensitive and simultaneously detection. |
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