Real-time detection of per-fluoroalkyl substance (PFAS) self-assembled monolayers in nanoporous interferometers

• Published in: Sensors and actuators. B, Chemical Vol. 355; p. 131340
• Main Authors: Law, Cheryl Suwen, Wang, Juan, Gunenthiran, Satyathiran, Lim, Siew Yee, Abell, Andrew D., Ahrens, Lutz, Kumeria, Tushar, Santos, Abel, Voelcker, Nicolas H.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15-03-2022; Elsevier Science Ltd
• Subjects: Aluminum oxide; Deionization; Functional groups; Fysikalisk kemi; Interferometers; Monolayers; Nanoporous anodic alumina; Optical thickness; Parameter sensitivity; Perfluoro compounds; Perfluoroalkyl & polyfluoroalkyl substances; Perfluorooctanoic acid (PFOA); Perfluorosilanes; Physical Chemistry; Real time; Reflectometric interference spectroscopy; Selectivity; Self-assembled monolayers; Self-assembly; Reflectometric interference spectroscopy; Nanoporous anodic alumina; Perfluorosilanes; Self-assembled monolayers; Perfluorooctanoic acid (PFOA)
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2021.131340

Identification and quantification of per- and polyfluoroalkyl substances (PFASs) remain challenging due to their chemical diversity, and their inert optical and chemical nature. Here, we present an optical system integrating perfluorosilane-functionalized nanoporous anodic alumina (NAA) interferometers with reflectometric interference spectroscopy (RIfS) for real-time, label-free detection of self-assembled monolayers (SAMs) of perfluorooctanoic acid (PFOA) as a model PFAS. Measured changes in the effective optical thickness (ΔOTeff) of NAA interferometers made it possible to study the fluorous interaction-induced self-assembly of PFOA molecules with perfluorosilane functional molecules of varying length, in real time and in situ. Analysis of key sensing parameters—sensitivity, low limit of detection and linearity—allowed us to determine the most optimal molecular length of perfluorosilanes to maximize immobilization of PFOA onto functional surfaces. Freundlich and Langmuir isotherm models were adapted to experimentally acquired values of ΔOTeff to elucidate the mechanism of PFOA–perfluorosilane interactions. Interpretation of these models suggests that PFOA binds to perfluorosilanes functional groups immobilized onto the inner surface of NAA interferometers through a fluorous interaction-induced Freundlich mechanism. The potential real-life applicability of this system was demonstrated by detecting the formation of PFOA-based SAMs in aqueous matrices of varying complexity (i.e. ultrapure, deionized, tap, and river water). This study provides new insights into how functional surface chemistries can be engineered to maximize sensitivity and selectivity to PFAS, harnessing fluorous interactions—with implications for future deployable systems to detect and remove these emerging toxicants.
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•Label-free, optical monitoring of PFOA–SAMs formation in nanoporous anodic alumina (NAA) interferometers.•The fluorous interaction-induced self-assembly of between PFOA and perfluorosilanized NAA is found to follow a Freundlich mechanism.•Real-life environmental sensing was demonstrated through the detection of PFOA in various spiked aqueous-based matrices.