Selective and sensitive colorimetric cyanide recognition in aqueous medium and food samples based on Ni(II) complex chemosensor

[Display omitted] •A nickel complex (NiC) sensor with thiourea binding sites was developed for colorimetric sensing.•The detection limits of NiC toward CN− and S2– reached 3.54 × 10−8 and 2.87 × 10−8 M.•The interaction between NiC and analytes (CN– or S2–) results from deprotonation.•The colorimetric response is due to the intramolecular charge transfer mechanism.•NiC sensor was applied to detect CN− in the food samples. Since cyanide is highly toxic that can lead to respiratory arrest and death, it is important to develop practical diagnostic methods for the sensing of cyanide. In this study, the colorimetric sensing of cyanide was achieved by a nickel complex (NiC) sensor with thiourea binding sites. NiC was prepared and characterized by 1H NMR, single-crystal X-ray crystallography, FTIR, and Mass spectra. When the cyanide and sulfide ions were added to NiC sensor, the color changed from light yellow to canary yellow and pale yellow to golden yellow, respectively. NMR titration results confirmed that the colorimetric response toward cyanide resulted from the deprotonation and formation of a guest–host complex. A binding mechanism is proposed based on the mass spectra, 1H NMR titration, and stoichiometry studies. The binding constant and detection limit of the NiC sensor toward cyanide was also investigated. The detection limits of NiC toward cyanide and sulfide reached 35.4 nM and 28.7 nM, respectively, lower than the World Health Organization (WHO)-allowed cyanide concentration in drinking water. The NiC complex possesses high selectivity to cyanide and sulfide through deprotonation of the –NH- protons. The detection of trace amounts of cyanide ions in natural food samples, such as cassava flour and sprouting potatoes, was also achieved by the NiC sensor.