Functionalized 2-Hydrazinobenzothiazole with Bithiophene as a Colorimetric Sensor for Lethal Cyanide Ions and Its Application in Food Samples

Abstract

A newly synthesized Schiff's base 2-(2-([2,2'-bithiophen]-5-ylmethylene)hydrazinyl)benzothiazole (BT) was obtained from the condensation reaction between 2-hydrazinobenzothiazole and 2,2-bithiophene-5-carboxaldehyde. The prepared probe BT was subjected to a confirmation of the structural arrangement through NMR, FTIR, ESI-HRMS, and single-crystal XRD spectral analysis. The BT colorimetric sensor showed selectivity and sensitivity toward the cyanide (CN^-) ion over other common anions such as ClO₄^-, Cl^-, Br^-, F^-, I^-, NO₂^-, OH^-, HSO₄^-, and H₂PO₄^- in a partial aqueous system CH₃CN/H₂O (8:2, v/v). The probe BT detects CN^- with the lowest detection range as low as 1.33 × 10^-8 M (3.59 ppm); in comparison to that given by WHO guidelines, it is significantly lower. The stoichiometric interaction between the probe BT and analyte CN^- was found to be 1:1 (BT/CN^-) binding mode using Jobs plot, and further association binding affinity was calculated to be 6.64 × 10^-3 M^-1. Additionally, these results were further supported by the FTIR and DFT calculations, as well as the ¹H NMR titration analysis, which complemented the binding data. The sensor probe BT was successfully employed in a cotton swab test kit approach and also in smartphone-assisted applications for the determination of CN^- ions. Finally, the outstanding sensing properties of probe BT aided the quantitative detection of CN^- ions, and it could be further applied to a variety of food samples, including apple seeds, sprouting potatoes, and cassava.