Metal–Organic Framework MIL-101(Cr)-Based Sensor for the Selective Adsorption and Electrochemical Detection of Perfluorooctanesulfonate

Abstract Perfluorooctanesulfonate (PFOS) is a highly persistent and toxic per- and polyfluoroalkyl substance (PFAS) widely recognized for its serious risks to both environmental and human health. In this work, an electrochemical impedance spectroscopy (EIS)-based sensor was developed for PFOS detection by integrating a MIL-101(Cr) metal–organic framework (MOF) sensing layer on the working electrode and a nickel hexacyanoferrate (NiHCF)-modified counter electrode. This simple and practical two-electrode system utilizes the large pore size, high surface area, and chromium center of MIL-101(Cr) to enable strong electrostatic and host–guest interactions with PFOS, leading to pronounced changes in pore resistance upon adsorption. The fabricated sensor exhibits a linear relationship between PFOS concentrations and pore resistance, with the limit of detection reaching 10.13 ppt. Selectivity tests demonstrate that excess amounts of common PFAS analogs, humic acid, and inorganic salts do not significantly interfere with the PFOS signal. This was further validated by statistical analysis using one-way ANOVA followed by Dunnett’s test, which confirmed that most interference conditions are not significantly different from PFOS alone. The sensor also shows stable performance over repeated measurements and operates effectively within the pH range of 5–8. Lastly, sensing experiments involving real water samples verify the applicability of the device for the detection of PFOS in complex matrices.