Imidazo-phenanthroline based ratiometric optical sensing platform for cyanide and fluoride ions

The severe toxicity and widespread distribution of fluoride (F^-) and cyanide (CN^-) ions in various environmental matrices highlight the urgent need for their efficient and reliable detection methods. In this study, we present a fluorogenic imidazo-phenanthroline based probe (L) for selective detection of F^- and CN^- in semi-aqueous medium. Probe L exhibits a pronounced ratiometric fluorescence response upon interaction with these anions, driven by hydrogen bonding interaction involving the N-H group of the imidazole moiety. Notably, L enables clear discrimination of CN^- from other anions through a distinct color change, with an impressive detection limit in the nanomolar (nM) range. To enhance its practical applicability, paper-based sensing strips embedded with L were developed, effectively detecting CN^- and F^- under UV light illumination. The probe's exceptional sensitivity and selectivity could be attributed to the strong acidity of the N-H proton, facilitating efficient hydrogen bonding interactions followed by deprotonation. The binding mechanism was thoroughly investigated using Job's plot, NMR, and DFT analyses. Additionally, L demonstrated versatility in environmental and biological applications, successfully detecting cyanide and fluoride ions in soil samples and identifying F^- in live MCF-7 cell lines via blue fluorescence channel imaging.