Ru Nanozyme-Loaded Fluorinated Strong-Base Anion-Exchange Resin for Dual-Mode Optical Screening of Per- and Polyfluoroalkyl Substances (PFAS)

Abstract

Per- and polyfluoroalkyl substances (PFAS) pose persistent risks to water and food safety, highlighting the need for simple and portable screening methods. Herein, we developed a Ru nanozyme-loaded per-fluoropolyether (PFPE)-containing strong-base ion-exchange (IEX) resin, PFPE-IEX+@Ru, for dual-mode optical sensing of perfluorooctanoic acid (PFOA). The PFPE-IEX + resin enriched PFOA through the combined effects of electrostatic association and fluorous/hydrophobic affinity, while the Ru nanozyme converted PFOA adsorption into changes in 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation. Under optimized conditions, PFOA adsorption suppressed Ru-catalyzed TMB oxidation, leading to a decrease in absorbance at 652 nm and an increase in fluorescence emission at 405 nm. The assay achieved detection limits of 0.50 μg L−1 for the colorimetric mode and 0.19 μg L−1 for the fluorescence mode. XPS, zeta-potential analysis, and DFT calculations supported that PFOA adsorption altered the local interfacial environment of PFPE-IEX+@Ru. A smartphone-based RGB analysis program was further developed for portable colorimetry-based detection. The method showed acceptable recoveries in spiked water and pretreated milk samples. Beyond PFOA, PFOS and PFBA also produced measurable concentration-dependent colorimetric responses, indicating broader responsiveness toward the tested PFAS analytes. These findings suggest the potential of PFPE-IEX+@Ru for rapid PFAS screening, although unresolved PFAS mixtures cannot be quantitatively interpreted using a PFOA calibration curve because multiple responsive PFAS congeners contribute to the optical signal.