A colorimetric and turn-on fluorescent sensor for fluoride ions, based on 2-hydroxy-1-naphthalene formaldehyde bis-Schiff base, was readily synthesized. The sensor in DMSO exhibits high sensitivity and good selectivity for fluoride ions from aqueous media. The F−-response mechanism involves a hydrogen bonding and deprotonation process in the sensor, which induced color changes from pale yellow to deep yellow and prominent fluorescence enhancement. The response time of sensor S for fluoride ions reached the plateau region after less than 1 s. Test strips based on sensor S were prepared, the test strips could conveniently detect fluoride ions in solutions. The detection limit was determined to be 1.4 × 10−8 mol L−1 (2.66 × 10−4 ppm), which is far lower than the WHO guideline for drinking water at levels of about (5.3–7.9) × 10−3 mol L−1 (100.7–150.1) ppm. Thus the sensor can be used to detect fluoride ions in drinking water.
