Highly Sensitive "Covalent-Assembly" Fluorescent Probe for Cyanide Detection in Pure Aqueous Media and Real Water Samples

In order to achieve efficient reaction-based fluorogenic sensing of lethal cyanide ions in aqueous environmental matrices, we have rationally designed a fluorescent probe based on the promising "covalent-assembly" principle and an intramolecular crossed-benzoin reaction assisted by this nucleophilic analyte. An original synthetic route towards this unprecedented fluo-rescent cyanide chemodosimeter was devised. The unique structural features of this "covalent-assembly" probe enable its facile conversion into a green-yellow emissive pyronin through a water-compatible domino reaction triggered by cyanide anion, thus producing a strong "turn-on" fluorescence response centered at 555 nm. A set of different fluorescence-based assays have highlighted sensing performances of this probe, especially its ability to detect low concentrations of cyanide ions in phosphate buffer within the range of 100-200 nM, by means of a user-friendly portable fluorometer. From a practical point of view, we have shown that this sensing strategy was also effective in real water samples, thus producing a limit of detec-tion (LOD) range of 1-2 µM in line with World Health Organization recommendations. This study is an important step towards the popularization of the concept of "covalent-assembly" probes in the field of fluorescence-based environmental analysis, largely under-explored until now.