Highly Sensitive Ratiometric Chemosensor and Biomarker for Cyanide Ions in the Aqueous Medium

[Image: see text] A newly designed cyanide-selective chemosensor based on chromone containing benzothiazole groups [3-(2,3-dihydro-benzothiazol-2-yl)-chromen-4-one (DBTC)] was synthesized and structurally characterized by physico-chemical, spectroscopic, and single-crystal X-ray diffraction analyses. The compound DBTC can detect cyanide anions based on nucleophilic addition as low as 5.76 nM in dimethyl sulfoxide–N-(2-hydroxyethyl)piperazine-N′-ethanesulfonic acid buffer (20 mM, pH 7.4) (v/v = 1:3). The binding mode between receptor DBTC and cyanide nucleophile has also been demonstrated by experimental studies using various spectroscopic tools and theoretical studies, and the experimental work has also been verified by characterizing one supporting compound of similar probable structure of the final product formed between DBTC and cyanide ion (DBTC–CN compound) by single-crystal X-ray analysis for detailed structural analyses. In theoretical study, density functional theory procedures have been used to calculate the molecular structure and the calculation of the Fukui function for evaluation of the electrophilic properties of each individual acceptor atom. Furthermore, the efficacy of the probe (DBTC) to detect the distribution of CN(–) ions in living cells has been checked by acquiring the fluorescence image using a confocal microscope. Notably, the paper strips with DBTC were prepared, and these could serve as efficient and suitable CN(–) test kits successfully.