High-selectivity turn-on fluorescence-based fluoride ion detection using histidine-functionalized UiO-66-NH₂

Hisditine-functionalized UiO-66-NH₂ (UiO-66-NH₂@Hst) as a novel "turn-on" fluorescent probe to detect fluoride ions has been successfully synthesized using the solvothermal method. The results showed that fluoride ion detection gave the best fluorescence response in water media and no response was observed in non-polar solvents. Detection at pH 3-10 produces a relatively similar fluorescence response and decreases quite significantly at pH 11-13. UiO-66-NH₂@Hst is very selective and stable towards fluoride ions as evidenced by the appearance of blue luminescence under UV light (λ ₃₆₅ nm) compared to other ions. A possible mechanism for detecting fluoride ions is through the formation of hydrogen bonds, which results in incremental electron transfer from organic ligands to Zr-oxo clusters. The LoD value obtained in this study was 0.013 ppm, which is smaller than the maximum concentration of fluoride ions in drinking water samples (1.5 ppm) set by the World Health Organization (WHO). Therefore, UiO-66-NH₂@Hst can be a candidate fluorescence-based sensor for fluoride ions.