Fluorescence enhancement of CdSe/ZnS quantum dots induced by mercury ions and its applications to the on-site sensitive detection of mercury ions.

Abstract

The significant fluorescence enhancement of CdSe/ZnS quantum dots (QDs) induced by Hg2+ was observed for the first time based on a CdSe/ZnS QD-modified fiber nanoprobe. The fluorescence enhancement mechanism contributed to the Zn-to-Hg cation exchange in the ZnS shell, which allowed to form a HgxZn1-xS/CdSe heterojunction and increase the separation of electrons and holes and reduce the recombination rate. High concentrations of Hg2+ accelerated the generation of thefluorescence signal and lead to higherfluorescence intensity. The maximum fluorescence intensity increased more than eight times when Hg2+ concentration was 1µM.The characteristic time (θc), i.e.,the rising time to achievethe maximum fluorescence intensity, was linearly dependent on initial concentration of Hg2+ solution in accordance withour proposed theory. When the evanescent wave optofluidic fluorescence platform was used, the linear detection range and detection limit of Hg2+ were 5.0-1000nM and 0.80nM, respectively. The fiber nanoprobe can be applied to the rapid, sensitive, and accurate on-site detection of Hg2+ in real water samples without significant matrix effect. Our work paves a novel way to develop a simple and reliable nanoprobe for mercuric pollution control, and achieve the high quantum efficiency of QDs by limiting the diffusion of Hg2+ in the ZnS shell.