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

Abstract

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.