Electrochemical sensing of cationic per- and polyfluoroalkyl substances via dual-signal transduction

Cationic per- and polyfluoroalkyl substances (PFAS) are emerging environmental contaminants of growing concern, yet rapid and reliable sensing strategies remain scarce due to limited molecular selectivity and poor resistance to false-positive signals. Herein, we report a portable electrochemical sensor for perfluorooctane sulfonamide quaternary ammonium (PFOSAmS) based on a molecularly imprinted poly(4-hydroxybenzoic acid) membrane integrated onto a disposable screen-printed electrode. Molecular electrostatic potential analysis reveals strong anionic sites within the imprinted polymer that favor electrostatic attraction to the cationic headgroup of PFOSAmS, while the aromatic backbone provides hydrophobic domains complementary to the perfluorinated chain. The formation of imprinted cavities effectively enhances the selectivity for PFOSAmS over structurally related PFAS. Specific binding of PFOSAmS generates a dual electrochemical response, characterized by a decrease in probe current and a positive shift in redox potential, enabling intrinsic discrimination of false-positive signals. Nonspecific adsorption only reduces interfacial electron transfer without affecting the redox potential, whereas binding within the imprinted cavities disturbs the local electrostatic and dielectric environment, leading to a characteristic potential shift. Under optimized conditions, the sensor exhibits a detection range from 50 pM to 5 µM with a detection limit of 7 pM (5.1 ng/L). Selectivity evaluation against 20 potential interferents, including seven representative PFAS, confirms negligible influence. Practical detection of PFOSAmS in tap, bottled, and river water samples further demonstrates the robustness of the sensing platform. This work establishes a rapid, low-cost, and false-positive-resilient analytical tool for sensitive and accurate detection of cationic PFAS.