Sensitive detection of PFOA in environmental water based on Pt/MnO₂ nanozymes with engineered d-band structure

The perfluorooctanoic acid (PFOA) as a representative of perfluorinated and polyfluoroalkyl substances is strictly regulated worldwide due to its persistent and bioaccumulative toxicity. At present, the conventional methods are unsuitable for rapid on-site PFOA detection due to they requiring bulky instruments and complicated pretreatment procedure. To address this issue, platinum cluster-supported manganese dioxide (Pt/MnO₂) nanozymes with different crystal phases were prepared and applied to dual-mode colorimetric-photothermal detection of PFOA. Among the four polymorphs, Pt/β-MnO₂ displayed the strongest oxidase-like activity. Spectroscopic characterization and density functional theory calculations indicated that the β phase promotes interfacial electronic coupling between Pt clusters and MnO₂, leading to d-orbital modulation and faster charge transfer, thereby improving catalytic performance. On this basis, a self-calibrating dual-mode sensing platform was established. PFOA preferentially accumulates at the Pt/β-MnO₂ interface through hydrophobic and electrostatic interactions, blocking interfacial electron transfer and O₂ activation, and causing synchronized changes in colorimetric and photothermal signals. The platform showed strong resistance to matrix interference and performed well in spiked tap water, lake water, and river water samples. This work demonstrates the role of phase-dependent interfacial electronic interaction in nanozyme catalysis and offers a practical strategy for PFOA detection in aquatic environments.