Chromo-fluorogenic Detection of Cyanide Ion with a Cyanine Probe

The adverse health effects caused by specific anions underscore the importance of easy and straightforward anion recognition. Excessive levels of anions such as cyanide or nitrate can disturb physiological processes, leading to health problems. For instance, cyanide ions (CN⁻) are highly toxic, disrupting cellular respiration by inhibiting vital enzymes. However, cyanide is widely used in various industrial processes, including gold and silver extraction, metal electroplating as well as in the production of paper, textiles, and nitrile. Therefore, the selective and sensitive detection of cyanide ions is essential for human well-being, environmental preservation, and the advancement of scientific and medical knowledge in the context of cyanide exposure.

Nowadays, optical chemosensors designed for anion detection are highly attractive for biological and environmental applications because of their simplicity, cost-effectiveness, and real-time response, without requiring advanced equipment. Cyanine-based probes, in particular, offer numerous advantages as optical chemosensors, including high sensitivity, tunable optical properties, and biocompatibility, making them valuable tools in analytical chemistry and biosensing applications.

Following our previous work focused on the synthesis of a sulfo-cyanine dye and its evaluation as an optical chemosensor for cations, we now report its chromo-fluorogenic ability for anion detection. Chemosensing studies revealed that this compound exhibited remarkable selectivity and sensitivity for CN⁻ in acetonitrile solution, with a marked colour change from cyan to colourless and the fluorescence emission was switched off. The detection limit was estimated to be as low as 0.45 μM, and the binding mode was studied using NMR techniques.