Multi-Mimic Activities of Co₃O₄ Nanopolyhedrons and Application in Regulating the Content of Intracellular Hydrogen Peroxide/Oxygen

Herein, Co3O4 nanopolyhedrons with multi-mimics of peroxidase (POD)-, oxidase (OXD)-, catalase (CAT)-, and glutathione peroxidase (GPx)-like activities were developed and utilized in the application of regulating the level of cellular oxygen and hydrogen peroxide combined with polydopamine (PDA). It was found that the multi-mimic activities can be controlled by pH and the OXD- and POD-like activities were the best when the pH was 4 but became weak under weakly acidic or neutral conditions. Meanwhile, the CAT-like activity was the best under neutral and weakly acidic conditions, and the GPx-like activity was better in neutral conditions than in acidic conditions. According to the high CAT-like activity of Co3O4 nanopolyhedrons under weakly acidic conditions, especially at the tumor cell microenvironment, the Co3O4 nanopolyhedrons can catalytically transform the H2O2 into O2 without interferences from other mimic activities. After coating with PDA, the Co3O4@PDA with good biocompatibility and dispersion can also be catalyzed to produce O2 in the cellular microenvironment with high efficiency. The corresponding H2O2 and O2 fluorescent probes were used to monitor the process, and the main mechanisms were investigated through fluorescence spectra and confocal fluorescence microscopy. This work not only verifies the multi-enzyme properties of Co3O4 nanopolyhedrons but also provides a nanomaterial for the regulation of the content of H2O2 or O2 in cells by utilizing the CAT-like enzyme property of the nanomaterial. It is considered that the concentration variation of the active small molecules in the cell microenvironment regulated by nanoenzymes may provide some basis for cancer diagnosis and treatment.