That's where the device - SION-105 - comes in. It's portable, considerably cheaper than ones in use now, and can be used on-site by anyone. In addition, it is luminescent by default, but darkens when it encounters fluoride ions.
Measuring fluoride at low concentrations with sufficient accuracy is expensive and requires a well-equipped chemical lab.
Kyriakos Stylianou at EPFL Valais Wallis in Switzerland said SION-105 detects fluorides by adding only a few droplets of water and by monitoring the colour change of the metal-organic frameworks (MOFs).
The study was published in the Journal of the American Chemical Society.
Adding fluoride to water has been a common practice in many countries, including the US, Australia, Brazil, Malaysia, India and Vietnam, especially in low concentrations - below 1.5 mg/litre.
The World Health Organisation (WHO) has set 1.5 mg/litre as the maximum limit for fluoride in drinking water.