H2O2-Responsive Gold Nanoclusters @ Mesoporous Silica @ Manganese Dioxide Nanozyme for “Off/On” Modulation and Enhancement of Magnetic Resonance Imaging and Photodynamic Therapy

In order to achieve safe and high-efficient photodynamic therapy (PDT), it was a powerful strategy of constructing O₂-generated nanozyme with intelligent "off/on" modulation and enhancement. Herein, a kind of H₂O₂-responsive nanozyme was developed for off/on modulation and enhancement of magnetic resonance (MR) imaging and PDT, in which great amounts of gold nanoclusters (AuNCs) were loaded into mesoporous silica to form nanoassembly, and manganese dioxide (MnO₂) nanosheets were wrapped as switching shield shell (AuNCs@mSiO₂@MnO₂). In a neutral physiological environment, stable MnO₂ shells eliminated singlet oxygen (¹O₂) generation to switch off PDT and MR imaging. However, in an acidic tumor microenvironment, the MnO₂ shell reacted with H₂O₂, in which MnO₂ degradation switched on MR imaging and PDT, and the generated O₂ further enhanced PDT. H₂O₂-responsive MnO₂ degradation brought about excellent MR imaging with a longitudinal relaxation rate of 25.31 mM^-1 s^-1, and simultaneously sufficient O₂ generation guaranteed a 74% high ¹O₂ yield. Under the irradiation of a 635 nm laser, the viability of MDA-MB-435 cells was reduced to 4%, and the tumors completely disappeared, demonstrating strong PDT performance. Therefore, H₂O₂-responsive AuNCs@mSiO₂@MnO₂ nanozyme showed excellent off/on modulation and enhancement of MR imaging and PDT and was a promising intelligent nanoprobe for safe and high-efficiency theranostics.