A Highly Selective Hemicyanine-Based Turn-Off Fluorescent Sensor for Cyanide Detection in Food Samples

Cyanide is a highly toxic anion. Humans are commonly exposed to cyanide through the consumption of drinking water or by eating plants that contain cyanogenic glucosides, such as cassava, a key carbohydrate source in many diets. While numerous methods exist for cyanide detection, few are both cost-effective and simple enough for use by individuals without specialized training. In this work, we designed and synthesized a hemicyanine-based fluorescent sensor ZM-FES for the detection of cyanide (CN^-). Among the anions tested, the sensor showed high selectivity towards CN^-. The addition of CN^- to ZM-FES in aqueous solution (ACN/H₂O (1:1, v/v)) caused a dramatic decrease in the absorbance and fluorescence intensities. The detection mechanism was based on nucleophilic addition between CN^- and the indolium group, which was confirmed by ¹H NMR and mass spectral analysis. The fluorescence intensity plot as a function of CN^- concentration showed a good linear relationship in the range 0-10 µM, and the detection limit was calculated as 0.195 µM. Furthermore, the proposed detection approach can operate over a wide pH range from 2.1 to 9.3. Finally, ZM-FES was successfully utilized to detect CN^- in food samples and satisfactory results were obtained.