A novel water-soluble naked-eye probe with a large Stokes shift for selective optical sensing of Hg and its application in water samples and living cells

A water-soluble and colorimetric fluorescent probe with a large Stokes shift (139 nm) for rapidly detecting Hg, namely Hcy-mP, was synthesized by using an indole derivative and 2,4-dihydroxybenzaldehyde as starting materials. This probe demonstrates good selectivity for Hg over other metal ions including Ag, Pb, Cd, Cr, Zn, Fe, Co, Ni, Cu, K, Na, Mg, and Ca in aqueous solution. With the increase in concentration of Hg, the color of the solution changed from pale yellow to pink and the fluorescence intensity decreased slightly. When 5-equivalents of EDTA were added to the solution with Hg, the fluorescence intensity of this probe was restored. The probe has been applied to the detection of Hg in real water samples. Moreover, this probe was confirmed to have low cytotoxicity and excellent cell membrane permeability. The effect of Hcy-mP-Hg towards living cells by confocal fluorescence was also investigated.