Adding fluoride to water has been common practice in a number of countries including the U.S. In low concentrations (below 1.5 mg/L), fluoride can help prevent tooth decay and strengthen bones; however, at higher levels, it can have the opposite effect, causing serious dental and bone disease, especially in children and developing fetuses. To determine whether drinking water is safe, fluoride must be detected in water at a parts-per-million (ppm) level. Measuring fluoride at such low concentrations with sufficient accuracy is expensive and requires a well-equipped chemical lab.
A device was developed that can accurately measure fluoride concentrations using only a few drops of water even with low-level contamination, resulting in a simple change in color brightness. The device, named SION-105, is portable, considerably less expensive than current methods, and can be used on-site by virtually anyone.
The key to the device design is a novel material that was synthesized (SION-105). The material belongs to the family of metal-organic frameworks (MOFs) — compounds made up of a metal ion (or a cluster of metal ions) connected to organic ligands, thus forming one-, two-, or three-dimensional structures. Because of their structural versatility, MOFs can be used in an ever-growing list of applications such as separating petrochemicals, detoxing water, and removing hydrogen or gold from water.
SION-105 is luminescent but darkens when it encounters fluoride ions. Adding a few droplets of water and monitoring the color change of the MOF indicates whether it is safe to drink the water. The researchers used the device to determine the fluoride content in different groundwater samples from three geographic areas. The data corresponded very well when compared to measurements made using ion chromatography, a standard method for measuring fluoride concentration in water.