PFAS, a group of highly fluorinated substances, pose a danger to humans and the environment. Particularly problematic members of this family, such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), appear to cause organ damage and cancer, as well as being endocrine disruptors.

In the magazine Angewandte Chemie researchers have presented a new method to create a cost-effective, easy-to-use fluorescent sensor for sensitive in situ testing of PFAS in water samples.

The term per- and polyfluoroalkyl substances (PFAS) refers to a group of organic compounds in which most or all of the hydrogen atoms attached to the carbon atoms are replaced by fluorine atoms. They are used to provide water, oil, and dirt resistance to a variety of products, such as nonstick pans, outdoor clothing, and packaging. They can also be found in firefighting foam, paint, and car polish.

These compounds are very useful and very dangerous when released into the environment: they do not break down and therefore do not concentrate in plants, animals and humans.

In the EU, a limit has been set for drinking water of 100 ng/l for individual specific PFAS substances and 500 ng/l for the total amount of all PFAS. In Germany, water suppliers must start testing drinking water for PFAS in 2026. The US Environmental Protection Agency has set stricter limits: For the most common PFASs (PFOS and PFOA), the upper limit is set at 4 nm/L for each substance.

The traditional method used to detect such small quantities involves chromatography and mass spectrometry, is time-consuming and expensive, and requires advanced equipment and skilled personnel. Timothy M. Swager and Alberto Consellon from the Massachusetts Institute of Technology (MIT) in Cambridge, USA, presented a technique to make a portable, low-cost test that uses fluorescence measurements to easily and selectively detect PFAS in water samples.

The test is based on a polymer with fluorinated side chains containing fluorinated dye molecules (square derivatives), in the form of a thin film or nanoparticle. A special polymer base (polyphenylene ethylene) absorbs violet light and transfers the light energy to the dye via electron exchange (Dexter mechanism).

The dye then fluoresces red. If PFASs are present in the sample, they enter the polymer and convert the dye molecules into nanometer particles. This is enough to stop the exchange of electrons and therefore the transfer of energy. The red fluorescence of the dye is “off” and the blue fluorescence of the polymer is “on”. The degree of change in fluorescence is proportional to the PFAS concentration.

This new technique, which has a detection limit in the μg/L range for PFOA and PFOS, is suitable for in situ detection in heavily polluted areas. Detection of trace amounts of these contaminants in drinking water can be achieved with sufficient accuracy after preconcentration of samples using solid phase extraction.