A novel fluorescein-coumarin-based fluorescent probe for fluoride ions and its applications in imaging of living cells and zebrafish in vivo

•A novel ratiometric fluorescent probe Flu-Si was designed and synthesized for F− detection.•The probe has excellent selectivity and anti-interference for F−. The detection limit was 0.025 μmol L−1.•The novel probe demonstrated fluorescence imaging of F− in living cells and zebrafish, suggesting its potential in clinical diagnostics.