A naphthalimide-based azo colorimetric and ratiometric probe: synthesis and its application in rapid detection of cyanide anions

Abstract

A naphthalimide-based azo dye (1) used as a colorimetric and ratiometric probe for the detection of CN⁻ was synthesized by incorporating a salicylaldehyde moiety, which acts as a recognition unit, to the naphthalimido diazonium salt. Upon reacting with CN⁻, probe 1 displays dramatic colour changes rapidly from yellowish to red, corresponding to the absorption band shift from 408 nm to 497 nm. The colorimetric probe allows ratiometric detection of CN⁻ with a linear range of 2–45 μM and a LOD (limit of detection) of 0.4 μM. In the optimized H₂O/DMSO (7/3, v/v) mixed solvent, probe 1 displays excellent selectivity for CN⁻ over other anions. In addition, 1 was successfully employed to prepare the filter paper-based test strips which can be used to monitor CN⁻ conveniently, and the discernible concentration of CN⁻ can be as low as 20 μM.