Synthesis, cytotoxicity and bioimaging of a novel Hg2+ selective fluorogenic chemosensor

Abstract

A rhodamine B derivative 2 with a terminal mercapto thiadiazole moiety was successfully synthesized and applied for selective recognition of Hg²⁺ in aqueous–acetonitrile (1 : 1, v/v, pH 7) solution by employing its photophysical properties. Low toxicity and precise cell-permeability of the ligand were used to probe in vitro intracellular mercury contamination using L-929 cells (mouse fibroblast cells) and BHK-21 (hamster kidney fibroblast) through a confocal fluorescence microscopic experiment and bio-imaging results showed the equal applicability of the ligand toward both tested cell lines. Meanwhile, it exhibited distinct Hg²⁺ induced increment in the fluorescence and absorption intensities with induction of an apparent colorimetric change from colorless to reddish pink, providing naked eye mercury detection based on the metal-promoted intramolecular electronic rearrangement in the probe molecule. The probe responds selectively to Hg²⁺ over various competitive cations (Sc³⁺, Yb³⁺, In³⁺, Ce³⁺, Sm³⁺, Cr³⁺, Sn²⁺, Pb²⁺, Fe²⁺, Ni²⁺, Co²⁺, Cu²⁺, Ba²⁺, Ca²⁺, Mg²⁺, Ag⁺, Cs⁺, Cu⁺, and K⁺) with marked fluorogenic response and selective colorimetric changes with high sensitivity of 30 nM. We expect that the proposed method will serve as a practical tool for environmental sample analysis and biological studies.