A colorimetric and ratiometric fluorescent probe for cyanide sensing in aqueous media and live cells

A novel probe, 3-benzyl-2-(N-ethylcarbazole-3-vinyl)-benzothiazolium bromide (L), was synthesized and utilized for the specific detection of cyanide ions in neutral aqueous solution (HEPES buffer, pH 7.4). This probe displays a fast response through visible colorimetric and fluorogenic changes toward CN−, allowing for ratiometric sensing of cyanide in aqueous media. The ratiometric response is due to the breaking of the extensive π-conjugation and the intramolecular charge transfer (ICT) by the nucleophilic conjugation addition of cyanide to L, which is ascertained by NMR and ESI-MS analysis as well as density functional theory (DFT) calculations. The detection limit of CN− (3.39 × 10−7 M) is well below the limit recommended in the World Health Organization (WHO) guidelines for drinking water. Moreover, fluorescence co-localization studies demonstrate that L is a specific mitochondria-targeting fluorescent probe. As far as we are aware, compound L is the first mitochondria-targeting probe for cyanide detection and can be used for sensing CN− in living cells with dual channel ratiometric fluorescence imaging.