Widespread, persistent, and toxic per- and polyfluoroalkyl substances (PFAS) pose a major threat to both water systems and human health. Current PFAS detection methods are prohibitively expensive, slow, and complex. To combat PFAS contamination and meet increasingly stringent regulations of PFAS in drinking water, the development of highly sensitive and selective PFAS sensing techniques is imperative. Herein, we present an ultrasensitive sensing platform for perfluorooctane sulfonic acid (PFOS) detection in tap water with a reporting limit (~250 ppq) lower than the maximum contaminant level (4 ppt) set by the U.S. Environmental Protection Agency, using remote gate field-effect transistor (RGFET) sensors featuring β-cyclodextrin (β-CD)-modified reduced graphene oxide as the sensing membrane. The detection range (100s ppq to 100s ppt) of the sensors matches well with environmentally relevant PFOS concentrations. The sensor exhibits excellent selectivity against common inorganic ions (e.g., Na⁺, K⁺, Ca²⁺, Cl^-, HPO₄^-, SO₄^2- ) and select organic pollutants (e.g., trichloroacetic acid) in tap water. Importantly, the reversible and rapid response (< 2 min) indicates the potential of RGFET for continuous inline monitoring of PFAS. Quartz crystal microbalance experiments provided further insights into the analyte adsorption behavior at the sensing surface and emphasize the critical role of both analyte adsorption and charge properties of analytes and buffers in generating sensing signals. The binding nature between β-CD probe and PFOS or interferent molecules, as well as the spatially resolved selectivity revealed by molecular dynamics simulations, suggest rational probe engineering strategies for future selective capture probe design.

Andrew Ferguson

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