Selective detection of sulfide in human lung cancer cells with a blue-fluorescent “ON-OFF-ON” benzimidazole-based chemosensor ensemble

A completely water-soluble, high quantum yield blue-fluorescent benzimidazole derivative (AQ), containing a rigid benzimidazole-thiophene structure, was synthesized. Among 21 metal ions, the fluorescence ofAQwas selectively turned off by Cu²⁺to form anAQ-Cu²⁺ensemble. Thereafter, the fluorescence of theAQ-Cu²⁺ensemble was turned on by sulfide (S^2-) with high selectivity and sensitivity in pure water solution. In comparison withAQ-Ag⁺andAQ-Hg²⁺ensembles,AQ-Cu²⁺was the only ensemble that was capable of detecting a sulfide anion. Also, the fluorescence intensity ofAQwas linearly proportional to the concentration of Cu²⁺and S^2-. Both Cu²⁺and S^2-were detected within a minutein vitro. Moreover,AQworked best in the pH range of 5-10 and had a limit of detection of 50 nM and 354 nM for Cu²⁺and S^2-respectively. It was employed for the detection of sulfide in human lung cancer A549 cells with low cytotoxicity.