Polyvinylidene fluoride coated optical fibre for detecting perfluorinated chemicals

This work reports the development of a Fabry-Perot Interferometry (FPI) based optical fibre to detect perfluorooctanoic acid (PFOA) and other perfluoroalkyl substances (PFAS) in aqueous solutions. A novel and simple sensor fabrication procedure utilizing an immersion precipitation-based phase inversion process to form a thin polyvinylidene fluoride (PVDF) coating at the end-faces of freshly cleaved optical fibres is presented. The PVDF coating was rich in the electroactive beta-phase, which enhances dipole-dipole and hydrophobic interaction with PFAS at binding sites. Sensor testing with model PFOA solutions showed that the PVDF coated FPI optical fibre can detect PFOA. The change in optical path difference (OPD) with change in PFOA concentration was considered as a measure of sensitivity and it corresponded to a value of 0.9-5 nm/ppm for PFOA. In real PFAS solutions obtained from fire-fighting foams, the OPD was found to be significantly more sensitive at 178 nm/ppb.