Mesoporous Metal\nOxide Nanostructures via an Interfacial\nRedox-Mediated Deposition Strategy for a Paper-Based Glutathione Sensor

Controllable deposition of mesoporous metal oxides on\nvarious nanosubstrates\nis highly essential for the fabrication of functional composites or\ndevices, but it remains a significant challenge. Herein, we develop\na versatile interfacial redox-mediated deposition strategy for fabricating\nmesoporous metal oxides on diverse nanosubstrates with different compositions\nand structures. The deposition process involves the coating of polyphenols\nonto various nanosubstrates followed by an interfacial redox reaction\nbetween the polyphenol and oxidative metal source (e.g., KMnO<sub>4</sub>, K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub>). Mesoporous MnO<sub>2</sub> is utilized as a typical coating material. When employing\nmetal-phenolic colloidal spheres as a nanosubstrate and potassium\npermanganate as an oxidative metal source, mesoporous MnO<sub>2</sub> spheres with high specific surface area (258.7 m<sup>2</sup>/g),\nlarge pore size (5.1 nm), and well-preserved spherical shape (∼200\nnm in diameter) are successfully synthesized. Furthermore, various\nnanosubstrates with diverse shapes and compositions such as Ni(OH)<sub>2</sub> nanosheets, FeOOH nanorods, and commercial carbon nanotubes\nare applied. After being coated with polyphenols (e.g., tannic acid),\nsuccessful deposition of mesoporous MnO<sub>2</sub> on these nanosubstrates\nis achieved via our proposed interfacial redox-mediated deposition\nstrategy. The success in deposition relies on both surface-independent\nadhesion and reductive properties exhibited by polyphenol molecules.\nThe prepared mesoporous MnO<sub>2</sub> spheres exhibit excellent\noxidase-like activity, which enables their application in developing\na paper-based colorimetric sensor for detecting glutathione. The detection\nlimit of glutathione is 0.15 μM. This versatile interfacial\nredox-mediated deposition strategy provides an avenue for the deposition\nof mesoporous metal oxides on the surface of various nanomaterials.