Fluoride can be healthy in certain concentrations, but above a certain level it instead has the opposite effect, causing serious dental and bone diseases. While the cost and benefit of any substance use has to be carefully weighted, up until now, verification that water source isn’t contaminated—above just 2 ppm—has been the purview of well-equipped laboratories.

Researchers at EPFL in Lausanne, Switzerland, however, have come up with a technique that can accurately determine fluoride concentrations using only a few drops of water. The key to this development is a new compound known as SION-105, which is normally luminescent, but darkens when it encounters fluoride. This means that instead of more expensive laboratory equipment, UV LEDs can be used with a photodiode to quantitatively measure the substance’s appearance, and thus the quantity of fluoride in drinking water. 

From the images in EPFL’s write-up, the prototype test apparatus appears to utilize several commonly available components, including an Arduino Uno and small OLED display for user feedback.

Published in the Journal of the American Chemical Society (JACS), the device is named SION-105, is portable, considerably cheaper than current methods, and can be used on-site by virtually anyone.

The key to the device is the design of a novel material that the scientists synthesized (and after which the device is named). 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, e.g. separating petrochemicals, detoxing water, and getting hydrogen or even gold out of it.

SION-105 is luminescent by default, but darkens when it encounters fluoride ions. “Add a few droplets of water and by monitoring the color change of the MOF one can say whether it is safe to drink the water or not,” explains Mish Ebrahim, the paper’s first author. “This can now be done on-site, without any chemical expertise.”