Per- and polyfluoroalkyl substances (PFAS) are an emerging class of pervasive micropollutant with deleterious health effects. Current detection methods rely on the collection and transport of water samples to a centralized facility where chromatographic and spectrometric analyses are preformed; however, these methods are expensive, time consuming, and cannot be deployed for in-field analysis. Electrochemistry offers a promising alternative as it is cheap, efficient, and offers a deployable platform; however, the lack of chemical reactivity of PFAS species requires electrode surface functionalization with a molecularly imprinted polymer (MIP). Previously, such sensors have required a one-electron mediator (i.e., a ferrocene derivative) for detection. Natural waterways do not have an abundance of ferrocenyl compounds for quantification, implying that these mediators limit sensor practicality, deployability, and cost. Here, we take advantage of ambient oxygen present in river water to quantify one of the more harmful PFAS molecules, perfluorooctanesulfonate (PFOS), from 0 to 0.5 nM on a MIP-modified carbon substrate. Calibration curves were generated using differential pulse voltammetry and electrochemical impedance spectroscopy with oxygen as the mediator in river water. Importantly, we show that electrochemical impedance spectroscopy is superior to voltammetric techniques. Further, impedance provided a PFOS limit of detection of 3.4 pM and showed no change in sensor signal in the presence of the common interferents humic acid and chloride. These results are a necessary step forward in developing deployable sensors that act as a first line of defense for detecting PFAS contamination at its earliest onset. Additionally, we demonstrate the development of a flexible printed circuit electrode array (78 working electrodes) and multiplexing hardware which will enable future in-field multiplexed measurements for the simultaneous detection of multiples PFAS species.

Towards deployable electrochemical sensors for per- and polyfluoroalkyl substances

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