Selective Ratiometric Signaling of Hg2+ Ions by a Fluorescein-Coumarin Chemodosimeter

We prepared a new chemodosimeter by combining the two well-known fluorophores, coumarin and fluorescein. The compound described herein effectively signals Hg2+ ions by the selective mercuration of the xanthene moiety in both chromogenic and fluorogenic signaling modes. The turn-off type changes in the fluorescence of the fluorescein moiety can be conveniently followed by the ratiometric approach in reference to the coumarin emission. The chemodosimeter can signal Hg2+ ions at submillimolar concentrations in the presence of common coexisting metal ions in aqueous environments. The design of selective and sensitive signaling systems for biologically important metal ions has attracted much research interest. Hg2+ signaling is particularly important, because of its toxic impact on biological systems and the environment. Many of the Hg2+ signaling systems which have been designed suffered from on-off type signaling, due to the intrinsic quenching nature of Hg2+ ions. In view of this, a signaling system which exhibits turn-on type signaling or ratiometric sensing is highly desirable for the development of new Hg2+-selective signaling systems