MXene-Based Nanoconfined Ion Channels for Ultratrace Detection of Short-Chain Per- and Polyfluoroalkyl Substance Trifluoromethanesulfonic Acid and Its On-site Application

The urgent need for monitoring trifluoromethanesulfonic acid (TFMS), a widespread and highly persistent member of the ultrashort-chain per- and polyfluoroalkyl substances (PFAS) family, is hampered by the formidable challenge of developing a selective and sensitive sensing platform. Herein, we address this gap through designing a nanoconfined microenvironment by intercalating 4-trifluoromethy-benzylammonium bromide into MXene (MX/CF3BZA) to construct a highly selective channel for TFMS detection. The resulting MX/CF3BZA-based ion-selective electrodes (ISEs) achieve remarkable performance, exhibiting an ultralow detection limit (1.2 × 10^-11 M), which is over 1 × 10⁴-fold lower than that of conventional commercial ISEs, 17-fold enhancement in selectivity (K_ij ∼ 7 × 10^-3), and near-Nernstian sensitivity of 56.37 mV/decade. Quartz crystal microbalance measurements directly corroborate this superior performance, showing a 6.4-fold stronger affinity of MX/CF3BZA for TFMS compared with pristine MXene. Density functional theory calculations reveal that the CF3BZA modification creates a unique nanoconfined environment that integrates synergistic F-F, electrostatic, and anion-π interactions, reducing the permeation energy barrier for TFMS by 16.71 kcal/mol. Furthermore, we integrated the ISE into a smartphone-based platform, demonstrating its practical application for on-site TFMS detection. This study showcases the potential of precise interface engineering in advanced sensing platforms for ultrashort-chain PFAS and beyond.