A nanosized metal–organic framework for visual detection of fluoride ions with smartphone via colorimetric test kit

Fluoride ion (F − ) is an essential micronutrient in the human body, however, an abnormal large intake of F − can result in adverse effects, such as skeletal fluorosis or DNA damage. Therefore, it is of great significance to develop convenient assays for the visual detection of F − with high sensitivity. We rationally developed the nanosized iron-based metal organic frameworks (Fe-MOFs) by using 3,5-dicarboxybenzeneboronic acid as organic linkers and Fe 3+ as metal ions through the solvothermal method, which can be applied for detecting F − with high sensitivity and selectivity owing to the specific recognition of boronic acid groups towards F − and the strong binding affinity between F − and Fe 3+ . The Fe-MOFs possess excellent peroxidase-like activity, which can be effectively inhibited by F − . Moreover, a portable test kit for the determination of F − was developed by embedding Fe-MOFs into hydrogel, and the visual measurement of F − was realized based on smartphone by identifying the color signal of the oxidation of 3,3',5,5'-tetramethylbenzidine dihydrochloride. The output signal (R/G) was linear with F − concentration in the range of 10.0–200.0 μM. The Fe-MOFs-based colorimetric strategy is easy-operation, low-cost and equipment-free, which has been further applied to detect F − in the real water samples.