A highly selective probe for fluorometric sensing of cyanide in an aqueous solution and its application in...

A simple fluorescent probe (KS4) containing multiple reaction sites (phenolic -OH, imine and C = C bonds) is successfully synthesized and characterized using ¹H NMR, ¹³C NMR, mass and single crystal XRD techniques. KS4 exhibits high selectivity towards CN^- over a wide range of common anions in H₂O:DMSO (1:1 v/v) leading to an amazing turn-on fluorescence at 505 nm via deprotonation of the phenolic -OH group. The limit of detection (1.3 µM) for CN^- was much below the standard (1.9 µM) set by the World Health Organization (WHO). Stoichiometry of the interaction between KS4 and CN^- was ascertained as 1:1 by the Job's plot method and the binding constant was determined to be 1.5x10⁴ M^-1. Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) based theoretical insight has been appealed to understand the optical properties of KS4 before and after the addition of CN^- ion. The probe shows respectable real-time applicability for qualitative detection of CN^- in almond and cassava powder as well as quantification in real water samples with excellent recoveries (98.8 - 99.8%). In addition, KS4 is found to safe towards living HeLa cells and successfully applied to the detection of endogenous cyanide ions in HeLa cells.