Effects of surface functionalization on the electrosynthesis of molecularly imprinted polymers (MIPs) and the detection of per- and polyfluoroalkyl substances (PFAS)

Recently, the US Environmental Protection Agency (EPA) has established stringent maximum contaminant levels (MCLs) for multiple per- and polyfluoroalkyl substances (PFAS) in drinking water. These compounds pose substantial environmental and health risks due to their bioaccumulative properties. While low concentrations can be detected quantitatively and selectively by liquid chromatography with tandem mass spectrometry (LC-MS/MS), this technique is cost-prohibitive, time-consuming, and not suitable for rapid and on-site measurements. Electrochemical sensors have the potential to provide a fast and portable alternative with sufficient selectivity and sensitivity for early screening of potential contaminated sources. These sensors rely on a layer of molecularly imprinted polymers (MIPs) that are synthesized through electrochemical oxidation of monomers (<i>e.g.</i>, <i>o</i>-phenylenediamine, <i>o</i>-PD) in the presence of targeted molecules (<i>e.g.</i>, perfluorooctane sulfonic acid, PFOS) as the template for selective binding sites. In this study, we test the hypothesis that the physicochemical properties of the electrode surface dictate the electropolymerization of MIPs and the resulting physical morphology and sensing properties. Specifically, MIP-based sensors prepared on hydrophobic surfaces exhibit improved sensing performance toward PFOS than the ones prepared on hydrophilic surfaces. We attribute the increased sensitivity to the stronger attraction of the hydrophobic surfaces to PFOS during the electropolymerization, which leads to enhanced imprinting of the MIPs and more selective binding sites. Our results, with PFOS as a model compound, demonstrate the importance of surface functionalization to the formation, physical morphologies, and sensing properties of a promising class of materials for environmental monitoring.