An easily accessible fluorometric probe for selective cyanide detection via nucleophilic addition: Applications to environmental water samples, smartphone, and bio-imaging of fungi and plants.

The monitoring of cyanide (CN-) is of great significance due to its extreme toxicity to both humans and the environment. In this study, we report a convenient fluorescent sensor HNIC ((E)-7-hydroxy-8-(((2-((7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)amino)phenyl)imino)methyl)-2H-chromen-2-one) for detecting CN-. On addition of CN-, HNIC exhibited a blue fluorescence turn-on response in aqueous media. Moreover, HNIC could selectively monitor CN- over other interfering ions, with a detection limit of 4.43 μM. The reaction of CN- with HNIC was evaluated using Job plot at a 1:1 ratio. To elucidate the mechanism of the nucleophilic attack of CN- on HNIC, ESI-MS analysis, 1H NMR titration, and DFT studies were employed. HNIC showed potential for quantifying CN- in environmental water samples (mineral, tap, river, and drinking water). Furthermore, a smartphone application utilizing HNIC successfully monitored CN- concentrations in environmental samples. Importantly, HNIC could track CN- through bio-imaging in fungi and plants, including white beech mushrooms, onions, and radish sprouts. Therefore, HNIC could be employed as a useful tool for detecting highly toxic CN- by triggering the fluorescent turn-on.