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

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 the fluorescence signal and lead to higher fluorescence intensity. The maximum fluorescence intensity increased more than eight times when Hg2+ concentration was 1 mu M. The characteristic time (theta (c)), i.e., the rising time to achieve the maximum fluorescence intensity, was linearly dependent on initial concentration of Hg2+ solution in accordance with our proposed theory. When the evanescent wave optofluidic fluorescence platform was used, the linear detection range and detection limit of Hg2+ were 5.0-1000 nM and 0.80 nM, 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.Graphical abstract

Automated summary

The significant fluorescence enhancement of CdSe/ZnS quantum dots induced by Hg2+ was observed for the first time using a CdSe/ZnS QD-modified fiber nanoprobe. The fluorescence enhancement mechanism was attributed to Zn-to-Hg cation exchange in the ZnS shell, forming a HgxZn1-xS/CdSe heterojunction. The maximum fluorescence intensity increased over eight times and the characteristic time was linearly dependent on Hg2+ concentration.