Colorimetric reversibility: Aqueous phase recognition of cyanide using smart phone-based device with real sample analysis

Abstract

A novel colorimetric 2-hydrazinobenzothiazole based probe (BTHP) was successfully synthesized and employed as an optical cyanide sensor. The interaction of CN⁻ with BTHP produced a distinct color variation (dark pink color) with a red shift (96 nm) in its absorption spectra. The probe was selective, sensitive and robust towards cyanide ion sensing even in the presence of other competing ions. It could detect cyanide ion upto 0.77 µM, even lower than the limit recommended by WHO (1.9 µM). The binding stoichiometry for BTHP-CN⁻ complex (1:1) was confirmed via Job’s plot. A binding constant of 3.19*10² M⁻¹ was calculated in the recognition process. The cyanide ion recognition mechanism was confirmed using ¹H NMR titration and DFT calculation. The probe coated filter paper test strips displayed dark pink color upon cyanide exposure. BTHP can be used reversibly for the visible detection of cyanide in liquid (real water) as well as solid phase (soil). Further, the practical applications of the developed sensor include smartphone based sensing, logic gate fabrication, molecular keypad lock and write-read-erase-read devices.