Fluorescent chemosensors for Hg2+ detection in aqueous environment

Abstract

Mercury is a pollutant extremely toxic to the environment and human health. Although numerous methods have been reported for the analysis of Hg2+ ions in water, the development of simple, rapid, inexpensive, and sensitive sensors still represents a challenge. Here, we describe the design, synthesis and spectral characterization of a set of dansyl-amino acids able to recognize Hg2+ ions via different fluorescence emission modes. The analysis of the binding features of the different chemosensors shows that the stoichiometry of the sensor–Hg2+ complex depends on the concentration of the sensor and Hg2+ since it plays an important role in the type of response for Hg2+ ions. Among those studied here N-dansylated methionine is the best performing chemosensor in terms of sensitivity with a LOD of 140nM. To improve the LOD of this chemosensor, we evaluated the response of a portable experimental set-up based on optical fiber probes. The new device shows an increase of LOD from 140nM to about 5nM, which can meet the requirements imposed by the Environmental Protection Agency for monitoring Hg2+ in drinkable water. We also show that the chemosensors are not applicable to marine water-based matrices because of the significant coordinating ability of chloride anions with Hg2+.