A novel water-soluble naked-eye probe with a large Stokes shift for selective optical sensing of Hg2+ and its application in water samples and living cells

Abstract

A water-soluble and colorimetric fluorescent probe with a large Stokes shift (139 nm) for rapidly detecting Hg²⁺, namely Hcy-mP, was synthesized by using an indole derivative and 2,4-dihydroxybenzaldehyde as starting materials. This probe demonstrates good selectivity for Hg²⁺ over other metal ions including Ag⁺, Pb²⁺, Cd²⁺, Cr³⁺, Zn²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, K⁺, Na⁺, Mg²⁺, and Ca²⁺ in aqueous solution. With the increase in concentration of Hg²⁺, 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 Hg²⁺, the fluorescence intensity of this probe was restored. The probe has been applied to the detection of Hg²⁺ in real water samples. Moreover, this probe was confirmed to have low cytotoxicity and excellent cell membrane permeability. The effect of Hcy-mP–Hg²⁺ towards living cells by confocal fluorescence was also investigated.