Direct and Rapid Sensing of Per- and Polyfluoroalkyl Substances Using SERS-Active Optical Fibers

Per- and polyfluoroalkyl substances (PFAS) are emerging contaminants with widespread usage and remarkable environmental stability. The available optical sensing methods typically exploit the hydrophobic and oleophobic properties of PFAS to induce the aggregation of other substances and achieve indirect detection of PFAS. In this paper, we directly measure the surface-enhanced Raman scattering (SERS) spectra of PFAS themselves based on microstructured optical fibers decorated with β-cyclodextrin and silver nanoparticles. β-cyclodextrin forms host–guest complexes with PFAS, accessing the hot spots of silver nanoparticles. Simultaneously, the microfluidic channels and light waveguide within the microstructured optical fibers greatly extend the interaction length between the excitation laser light and PFAS. This platform enables rapid and sensitive PFAS sensing with characteristic peaks emerging upon liquid introduction into the optical fibers and a detection limit as low as 40 ng/L for perfluorooctanoic acid. Furthermore, the effective differentiation of PFAS with similar structures but different C–F chain lengths and terminal functional groups is realized by combining SERS detection with principal component analysis (PCA).