Mesoporous Carbon Dot Architectures via Liquid–Liquid Phase Separation for Droplet-Mode Impedance Sensing of PFAS

Heightened concerns over perfluoroalkyl and polyfluoroalkyl substances (PFAS) have intensified the demand for cost-effective, rapid, and sensitive detection technologies. Carbon nanodots (C-dots), as emerging metal-free quantum dots, show strong potential for environmental sensing; however, their integration into solid-state platforms for PFAS detection remains limited. Here, we present a droplet-mode electrochemical impedance spectroscopy (EIS) platform that leverages liquid–liquid phase separation (LLPS) to direct the self-assembly of C-dots into mesoporous architectures on flexible indium tin oxide electrodes. By formulating ternary microdroplets and tracking their evaporation in situ, we capture intermediate LLPS states that control the pore morphology, with porosity aligning closely with theoretical predictions from ternary phase diagrams. These mesoporous electrodes exhibit enhanced PFAS adsorption and charge-transfer modulation, enabling a strong impedance response. The sensor achieves a detection limit of 2 ppb for perfluorooctanoic acid (PFOA) in spiked tap water and operates within a linear range of 10–200 ppb, all without sample pretreatment. Furthermore, as confirmed by theoretical and experimental analysis, the platform is adaptable to longer-chain PFAS, such as perfluorodecanoic acid (PFDA). This simple and tunable LLPS-based strategy offers a new route to engineer nanocarbon architectures for solid-state sensing and facilitates point-of-need monitoring of persistent environmental contaminants.