A reversible fluorescent sensor for continuous detection of fluoride ion and trace water in chemical reagents

Continuously monitorable fluorescence sensors can provide fast, immediate, in-field detection of analytes without tedious process. A simple fluorescent sensor (BN) constructed from naphthol Schiff base was developed for reversible monitoring of F^- and trace water. Sensor BN showed specific selectivity toward F^- over other anions giving rise to a fluorescence "turn-on" response. After added F^-, the BN solution caused a dramatically observable color change from non-fluorescence to blue-green, and the limit of detection reached 78.5 nM. The Job's and ¹H NMR analysis confirmed that the recognition mechanism could be concluded to F^- caused deprotonation of sensor BN by hydrogen bonding interaction. Moreover, the deprotonated form BN∙F obtained by using F^- was acted as excellent sensitivity sensor for trace water detection with instant response through reprotonation. After addition of trace water, the emission color and spectral signal of BN∙F reverted to the original BN sate with the limit of detection of 0.0011 %. The reversible detection characteristic was conducive to the development of an inkless writing and encryption device. And importantly, BN∙F was utilized as a promising fluorescent sensor in the quantitative determination of water content in routinely chemical reagents.