Reaction‐Based Ratiometric Chemosensor for Instant Detection of Cyanide in Water with High Selectivity and Sensitivity

A highly selective chemosensor 1 based on an acylhydrazone group as binding site and naphthalene group as the fluorescence signal group were described, which could instantly detect CN − in water with specific selectivity and high sensitivity. The detection of cyanide was performed via the nucleophilic attack of cyanide anion on the carbonyl group, which could be confirmed by 1 H NMR, 13 C NMR, ESI‐MS and DFT calculations. The addition of CN − to sensor 1 induced a remarkable color change from colorless to yellow and generated a blue fluorescence, these sense procedure could not interfered by other coexistent competitive anions (F − , Cl − , Br − , I − , AcO − , H 2 PO 4 − , HSO 4 − , ClO 4 − , SCN − , S 2− , NO 3 − and SO 4 2− ). The detection limits were 5.0×10 −7   M and 2.0×10 −9   M of CN − using the visual fluorescent color changes and fluorescence spectra changes respectively, which is far lower than the WHO guideline of 1.9×10 −6   M . Test strips based on sensor 1 were fabricated, which could act as a convenient and efficient CN − test kit to detect CN − in pure water for “in‐the‐field” measurement.