Honeycomb-Satellite Structured pH/H₂O₂-Responsive Degradable Nanoplatform for Efficient Photodynamic Therapy and Multimodal Imaging

The oxygen-deprived environment of a solid tumor is still great restriction in achieving an efficient photodynamic therapy (PDT). In this work, we developed a smart pH-controllable and H2O2-responsive nanoplatform with degradable property, which was based on honeycomb manganese oxide (hMnO2) nanospheres loaded with Ce6-sensitized core-shell-shell structured up-conversion nanoparticles (NaGdF4:Yb/Er,Tm@NaGdF4:Yb@NaNdF4:Yb) (abbreviated as hMUC). In the system, the speedy breakup of the as-prepared hMnO2 nanostructures results in release of loaded Ce6-sensitized UCNPs under the condition of H2O2 in acid solution. When exposed to tissue-penetrable 808 nm laser, up-conversion nanoparticles (UCNPs) emit higher-energy visible photons which would be absorbed by Ce6 to yield cytotoxic reactive oxygen species (ROS), thus triggering PDT treatment naturally. Moreover, the in vitro and in vivo experiments demonstrate that hMUC sample with the honeycomb-satellite structure can serve as multimodal bioimaging contrast agent for self-enhanced upconversion luminescence (UCL), magnetic resonance imaging (MRI) and computed tomography (CT) imaging, indicating that the as-prepared hMUC could be used in imaging-guided diagnosis and treatment, which has a potential application in the PDT treatment of tumor.