Application of 2,4,5-tris(2-pyridyl)imidazole as 'turn-off' fluorescence sensor for Cu(II) and Hg(II) ions and in vitro cell imaging.

The 2,4,5-tris(2-pyridyl)imidazole (L) molecule has been evaluated as a probe for dual sensing of Hg 2+ and Cu 2+ ions in EtOH/HEPES buffer medium (5 mM, pH = 7.34, 1:1, v/v). Probe L shows a good sensitive and selective turn-off response in the presence of both Hg 2+ and Cu 2+ ions, which is comprehensible under long UV light. The probe can detect Cu 2+ ion in the pH range 3-11 and Hg 2+ ion in pH 6-8. The limit of detection for Cu 2+ (0.77 μM) is well under the allowable limit prescribed by the United States Environmental Protection Agency. Two metal (Cu 2+ /Hg 2+ ) ions are needed per L for complete fluorescence quenching. The probe shows marked reversibility on treatment with Na 2 EDTA, making the protocol more economical for practical purposes. Paper strip coated with the L solution of EtOH can detect the presence of Cu 2+ and Hg 2+ ions in the sample using visible quenching of the fluorescence intensity. Density functional theory-time-dependent density functional theory (DFT-TDDFT) calculations support experimental observations, and d-orbitals of Cu 2+ /Hg 2+ provide a nonradiative decay pathway. Cell imaging study using HDF and MDA-MB-231 cells also supported the viability of L in detecting Cu 2+ and Hg 2+ ions in living cells.