Organic Electrochemical Transistors with Molecularly Imprinted Polymer Electrodes for Rapid Detection of Perfluorooctanoic Acid

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants linked to adverse health effects, and there is a need for sensors that can detect PFAS in challenging environments. Electrochemical sensors offer significant potential for achieving cost-effective, rapid, and real-time detection of PFAS, particularly in comparison to current detection techniques, which rely on costly chromatographic methods. Here, we report that organic electrochemical transistors (OECTs) containing a molecularly imprinted polymer (MIP) gate electrode can selectively detect perfluorooctanoic acid (PFOA) in seawater. We prepared a molecularly imprinted polyaniline (PANI) gate electrode by polymerizing aniline onto filter paper in the presence of PFOA, followed by rinsing to remove the PFOA. When used as a gate electrode in an organic electrochemical device (OECT), the presence of PFOA produced a measurable change in the OECT source-drain current due to adsorption of PFOA onto the gate electrode, which reduced capacitance and increased impedance. Other molecules produced a weak or no response. Specifically, we show that the device responds strongly to PFOA but only weakly to perfluoropropionic acid (PFPrA), perfluorohexanoic acid (PFHxA), and surfactant 4-dodecylbenzenesulfonic acid (DBSA). The device is also able to selectively detect PFOA in mixtures containing these other PFAS or surfactants. We achieved a detection limit of 1.6 parts per trillion (ppt) or 3.86 × 10^-12 M, below the regulatory advisory level of 70 ppt set by the United States Environmental Protection Agency for PFOA. This work demonstrates low-cost sensors capable of rapid and molecularly specific detection of PFOA, which can potentially lead to low-cost sensors for monitoring the concentrations of PFOA and other PFAS in seawater and other challenging environments.