Ratiometric fluorescent and chromogenic chemodosimeter for cyanide detection in water and its application in bioimaging

Abstract

An indole conjugated thiophene–pyridyl (ITP) sensor for cyanide has been synthesized and characterized using NMR and mass spectroscopy. The selectivity of ITP has been explored in aqueous solution, and the resulting ratiometric fluorescence response toward CN⁻, among 11 different anions, was studied. The complexation of ITP–CN has been addressed using HRMS, ¹H-NMR, and UV-vis spectroscopy. ITP displays substantial dual changes in both its ratiometric emission and absorption spectra, exclusively in the presence of CN⁻ in aqueous solution. This is due to the nucleophilic attack of the indolium group of ITP by CN⁻, which induces a ratiometric fluorescence change and consequently a large emission shift. DFT/TDDFT calculations were performed in order to demonstrate the electronic properties of ITP and the ITP–CN adduct. The resultant ITP–CN adduct was used as a secondary sensing chemo-ensemble for the detection of cyanophilic metal ion-containing molecules by removing CN⁻ from ITP–CN and regenerating ITP with switch-on red fluorescence. For the practical application of the sensor, test strips based on ITP were made up, which could act as suitable and proficient kits for CN⁻ testing and cell studies.