Freestanding and Flexible β-MnO₂@Carbon Sheet for Application as a Highly Sensitive Dimethyl Methylphosphonate Sensor

Research on wearable sensor systems is mostly conducted on freestanding polymer substrates such as poly(dimethylsiloxane) and poly(ethylene terephthalate). However, the use of these polymers as substrates requires the introduction of transducer materials on their surface, which causes many problems related to the contact with the transducer components. In this study, we propose a freestanding flexible sensor electrode based on a β-MnO₂-decorated carbon nanofiber sheet (β-MnO₂@CNF) to detect dimethyl methylphosphonate (DMMP) as a nerve agent simulant. To introduce MnO₂ on the surface of the substrate, polypyrrole coated on poly(acrylonitrile) (PPy@PAN) was reacted with a MnO₂ precursor. Then, phase transfer of PPy@PAN and MnO₂ to carbon and β-MnO₂, respectively, was induced by heat treatment. The β-MnO₂@CNF sheet electrode showed excellent sensitivity toward the target analyte DMMP (down to 0.1 ppb), as well as high selectivity, reversibility, and stability.