Differential Recognition of Structurally Related PFAS by a Near-Infrared Fluorescent Probe through Opposite Spectral Shifts

Rapid discrimination of structurally related per- and polyfluoroalkyl substances (PFAS) in water-rich media remains highly challenging, due to high background signals and poor differentiation capability. In this work, a cationic near-infrared fluorescent probe, TAS-2, was identified from an alkyl-chain-engineered probe family (TASs) as an effective probe for differential PFAS recognition in water-rich medium. Among TASs, TAS-2 showed the lowest fluorescence background in the most water-rich medium, making it the most suitable candidate for aqueous PFAS sensing. Benefiting from its analyte-dependent aggregation-induced near-infrared fluorescence emission behavior, TAS-2 enabled differential recognition of representative PFAS. Specifically, PFOS and PFHxS induced blue-shifted emission, whereas PFOA produced a slight red-shifted response. This opposite-shift behavior provided a direct spectral basis for distinguishing structurally related PFAS. Mechanistic studies suggested that electrostatic attraction between cationic TAS-2 and anionic PFAS headgroups drives PFAS-promoted aggregation, while molecular dynamics simulations indicated that different PFAS induce distinct conformational arrangements of TAS-2 assemblies, contributing to their divergent emission-shift behaviors. In addition, TAS-2 exhibited low cytotoxicity and enabled concentration-dependent fluorescence imaging in living cells and Daphnia magna. These results demonstrate an alkyl-chain engineering strategy for low-background near-infrared fluorescent probes and provide a spectral fingerprint-based approach for the single-probe discrimination of structurally related PFAS in water-rich media.