How perfluoroalkyl substances modify fluorinated self-assembled monolayer architectures: An electrochemical and computational study

Abstract

There is an urgent need for sensing strategies to screen perfluoroalkyl substances (PFAS) in aqueous matrices. These strategies must be applicable in large-scale monitoring plans to face the ubiquitous use of PFAS, their wide global spread, and their fast evolution towards short-chain, branched molecules. To this aim, the changes in fluorinated self-assembled monolayers (SAM) with different architectures (pinholes/defects-free and with randomized pinholes/defects) were studied upon exposure to both long and short-chain PFAS. The applicability of fluorinated SAM in PFAS sensing was evaluated. Changes in the SAM structures were characterised combining electrochemical impedance spectroscopy and voltammetric techniques. The experimental data interpretation was supported by molecular dynamics simulations to gain a more in-depth understanding of the interaction mechanisms involved. Pinhole/defect-free fluorinated SAM were found to be applicable to long-chain PFAS screening within switch-on sensing strategy, while a switch-off sensing strategy was reported for screening of both short/long-chain PFAS. These strategies confirmed the possibility to play on fluorophilic interactions when designing PFAS screening methods.

Keywords: 2,3,3,3-Tetrafluoro-2-(heptafluoropropoxy)-propanoate ammonium salt (HFPO-DA); Electrochemical sensing; Fluorosulfactant; Molecular dynamics simulations; PFAS; Perfluoroctanesulfonic acid potassium salt (PFOS); Perfluorooctanoic acid (PFOA); Self-assembled monolayer; per-fluoroalkyl substances.