Ordinarily, water samples are routinely checked for fluoride content in well-equipped labs. This is an important task, as fluctuating levels of naturally-occurring fluoride can combine with added fluoride to push the total concentration beyond acceptable limits. Unfortunately, though, towns in developing countries often lack such facilities. With that in mind, scientists from Switzerland's EPFL research institute developed a prototype device known as the SION-105.

It's named after a material that it utilizes – which was synthesized by the researchers – that's a type of metal-organic framework (MOF). This means that the material is made up of metal ions connected to organic ligands. And while the MOF is ordinarily luminescent, it darkens when exposed to fluoride ions.