A novel water-soluble naked-eye probe with a large Stokes shift for selective optical sensing of Hg(2+) 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(2+), namely Hcy-mP, was synthesized by using an indole derivative and 2,4-dihydroxybenzaldehyde as starting materials. This probe demonstrates good selectivity for Hg(2+) over other metal ions including Ag(+), Pb(2+), Cd(2+), Cr(3+), Zn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), K(+), Na(+), Mg(2+), and Ca(2+) in aqueous solution. With the increase in concentration of Hg(2+), 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(2+), the fluorescence intensity of this probe was restored. The probe has been applied to the detection of Hg(2+) in real water samples. Moreover, this probe was confirmed to have low cytotoxicity and excellent cell membrane permeability. The effect of Hcy-mP–Hg(2+) towards living cells by confocal fluorescence was also investigated.