Mesoporous Metal Oxide Nanostructures via an Interfacial Redox-Mediated Deposition Strategy for a Paper-Based Glutathione Sensor

Controllable deposition of mesoporous metal oxides on various nanosubstrates is highly essential for the fabrication of functional composites or devices, but it remains a significant challenge. Herein, we develop a versatile interfacial redox-mediated deposition strategy for fabricating mesoporous metal oxides on diverse nanosubstrates with different compositions and structures. The deposition process involves the coating of polyphenols onto various nanosubstrates followed by an interfacial redox reaction between the polyphenol and oxidative metal source (e.g., KMnO₄, K₂Cr₂O₇). Mesoporous MnO₂ is utilized as a typical coating material. When employing metal-phenolic colloidal spheres as a nanosubstrate and potassium permanganate as an oxidative metal source, mesoporous MnO₂ spheres with high specific surface area (258.7 m²/g), large pore size (5.1 nm), and well-preserved spherical shape (∼200 nm in diameter) are successfully synthesized. Furthermore, various nanosubstrates with diverse shapes and compositions such as Ni(OH)₂ nanosheets, FeOOH nanorods, and commercial carbon nanotubes are applied. After being coated with polyphenols (e.g., tannic acid), successful deposition of mesoporous MnO₂ on these nanosubstrates is achieved via our proposed interfacial redox-mediated deposition strategy. The success in deposition relies on both surface-independent adhesion and reductive properties exhibited by polyphenol molecules. The prepared mesoporous MnO₂ spheres exhibit excellent oxidase-like activity, which enables their application in developing a paper-based colorimetric sensor for detecting glutathione. The detection limit of glutathione is 0.15 μM. This versatile interfacial redox-mediated deposition strategy provides an avenue for the deposition of mesoporous metal oxides on the surface of various nanomaterials.