Fluorescent chemosensors for Hg2+ detection in aqueous environment

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 140 nM. 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 140 nM to about 5 nM, 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+. (C) 2017 Elsevier B.V. All rights reserved.