A novel hydrazide-based selective and sensitive optical chemosensor for the detection of Ni²⁺ ions: applications in live cell imaging, molecular logic gates and smart phone-based analysis

A novel flexible "N", "O"-rich hydrazide-based Schiff base chemoreceptor, 2-(benzamido)-N'-((pyridin-2-yl)methylene)benzohydrazide (L), was designed, synthesised and characterised via¹H-NMR, IR spectroscopy, ESI-MS spectrometry and single-crystal XRD analysis. The receptor showed a colorimetric and fluorometric "turn on" response in the presence of only Ni²⁺ ions in methanol-Tris-HCl buffer medium (10 mM, pH 7.2, 1 : 1 v/v). The Job plot analysis revealed that the receptor forms a 2 : 1 complex with Ni²⁺ ions, which was further confirmed via the ESI-MS analysis. A single crystal of the L-Ni²⁺ complex (2) was also isolated. The detection limit was calculated to be 1.8 μM colorimetrically and 1.18 μM fluorometrically, which are much lower than those recommended as per the WHO guidelines for drinking water. The experimental results were further supported by DFT studies. The chemosensor L was applied for the recovery of contaminated water samples, building of molecular logic gate, smart phone-based analysis and live cell imaging.