Detection of per- and polyfluoroalkyl water contaminants with a multiplexed 4D microcavities sensor

The per- and polyfluoroalkyl substances (PFAS) are a group of organofluorine chemicals treated as the emerging pollutants that are currently of particularly acute concern. These compounds have been employed intensively as surfactants over multiple decades and are already to be found in surface and ground waters at amounts sufficient to have an effect on human health and ecosystems. Because of the carbon–fluorine bonds, the PFAS have an extreme environmental persistence and their negative impact accumulates with further production and penetration into the environment. In Germany alone, more than thousands of sites have been identified as contaminated with PFAS; thus, timely detection of PFAS residue is becoming a high priority. In this paper, we report on the high performance optical detection method based on whispering gallery mode (WGM) microcavities applied for the first time to detect PFAS contaminants in aqueous solutions. A self-sensing boosted 4D microcavity fabricated with two-photon polymerization is employed as an individual sensing unit. In an example of the multiplexed imaging sensor with multiple hundreds of simultaneously interrogated microcavities we demonstrate the possibility to detect the PFAS chemicals representatives at a level down to 1 ppb (parts per billion).