Colorimetric and turn-on Fluorescence Chemosensor for Hg²⁺ Ion Detection in Aqueous Media

A new rhodamine 6G based fluorescent and colorimetric chemosensor, containing N-methyl imidazole nucleus, for the selective detection of Hg²⁺ ion was designed and synthesized. The results of UV-Vis and fluorescence spectral study indicated that the receptor is selective and sensitive towards Hg²⁺ with no noticeable interference with other competitive metal ions. The addition of Hg²⁺ to the receptor induced a rapid color change to pink from colorless and the turn-on fluorescence response toward Hg²⁺ among different cations was studied. The stoichiometric ratio of 1:1 between the receptor and Hg²⁺ was supported by Job's plot. The color change and turn-on fluorescence response upon addition of Hg²⁺ ion was ascribed by the spirolactam ring-opening mechanism. The probable mode of binding between the receptor and Hg²⁺ was confirmed by ¹H NMR and Mass spectral study. For the practical application, its electrospun nanofiber test strips successfully applied to recognize Hg²⁺ ion in aqueous media. Graphical Abstract Schematic representation of Hg²⁺ detection by rhodamine based sensor.