New device invented to simplify the measurement of fluoride contamination in water

Seeking to address fluoride contamination in drinking water, chemical engineers at EPFL have developed a portable and user-friendly device that can measure fluoride concentration accurately and reliably.

The prototype device used with SION-105 to detect fluoride anions in drinking water (credit: Marie-Thé and Etienne Roux).
The prototype device used with SION-105 to detect fluoride anions in drinking water (credit: Marie-Thé and Etienne Roux).

Fluoride is added to water in small concentrations by many public water suppliers to protect the teeth from decay and to build bone strength. Yet, in high concentrations (more than several parts per million) fluoride can harm human health.

According to WHO, the maximum permissible limit of fluoride in drinking water is 1.5 ppm and the highest desirable limit is 1.0 ppm. Fluoride concentrations above 1.5 ppm in drinking water cause dental fluorosis and much higher concentration skeletal fluorosis.

Defluoridation is difficult and expensive and requires a well-equipped chemical lab. Because of this, fluoride contamination in water affects a number of developing countries today and even parts of developed countries.

A diagram of the SION-105 prototype device: A vial containing a red luminescent suspension of SION-105 crystals is placed inside the device. When two drops of water sample are added to the vial, resulting changes in the brightness of SION-105 are measured by the photodiode, and instantly converted into an accurate quantitative reading of the fluoride concentration in the sample. The inset is a schematic of how the luminescence is quenched at the molecular level. Credit: Mish Ebrahim
A diagram of the SION-105 prototype device: A vial containing a red luminescent suspension of SION-105 crystals is placed inside the device. When two drops of water sample are added to the vial, resulting changes in the brightness of SION-105 are measured by the photodiode, and instantly converted into an accurate quantitative reading of the fluoride concentration in the sample. The inset is a schematic of how the luminescence is quenched at the molecular level. Credit: Mish Ebrahim

To find out the better solution for this problem, a team of scientists at the EPFL has developed a device to precisely measure fluoride concentrations using only a few drops of water- resulting in a simple change in color brightness.

Scientists dubbed this device as SION-105. It is portable, cheaper than existing methods and can be used on-site by virtually anyone.

To design this device, scientists used a material that belongs to the family of “metal-organic frameworks” (MOFs), compounds made up of a metal ion. They then connected it to organic ligands that thus form one-, two-, or three-dimensional structures.

A photograph of SION-105 suspended in solvents with (L) and without (R) fluoride ion contamination. Credit: Mish Ebrahim
A photograph of SION-105 suspended in solvents with (L) and without (R) fluoride ion contamination. Credit: Mish Ebrahim

Mish Ebrahim, the paper’s first author said, “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. This can now be done on-site, without any chemical expertise.”

Scientists tested the device by determining the fluoride content in different groundwater samples from Vietnam, the United Arab Emirates, and Saudi Arabia.

Kyriakos Stylianou at the Laboratory of molecular simulation said, “This comparison showcases the performance and reliability of SION-105, which, coupled with the portability and ease-of-use of the device, make it a very user-friendly solution for water sampling in remote areas where frequent fluoride concentration monitoring is paramount.”

Having confirmed the successful function of SION-105 and the device, EPFL has now filed a patent application for it. The device was developed by a scientist at the Laboratory of molecular simulation, the Laboratory of Organometallic and Medicinal Chemistry, and the Electronic Workshop at EPFL Valais Wallis.

The study is published in the Journal of the American Chemical Society.