Intelligent nanoenzyme for T1-weighted MRI guided theranostic applications

•PPy@MnO2-BSA(Ce6) NPs possess favorable biocompatibility and colloidal stability.•It could produce the cellular toxic reactive oxygen species to kill tumor.•PPy-PVP NPs exhibit high photothermal conversion ability.•PPy@MnO2-BSA(Ce6) NPs could relieve the hypoxia by catalyze H2O2 into oxygen.•PPy@MnO2-BSA(Ce6) NPs were used for imaging guided photo-therapy of tumor. In this research, a novel nanoenzyme-based theranostic nanoplatform, named PPy@MnO2-BSA (bovine serum albumin (BSA)-modified manganese dioxide (MnO2)/polypyrrole (PPy)) was invented for T1-MRI-guided combined photothermal therapy (PTT) and photodynamic therapy (PDT) of tumors. The materials design was based on the in-situ oxidation and polymerization of pyrrole, using potassium permanganate (KMnO4) as the oxidant. The formed PPy@MnO2-BSA was further used to load with Ce6, via physical absorption. The PPy, with a high absorbance within the near-infrared (NIR) region, endowes the nanoenzyme with outstanding photothermal performance with the photo-to-heat conversion efficiency of 21.05%, while the MnO2, which could reduce the relaxation time of nearby protons, serves to enhance the tumor T1-MRI ability. Moreover, upon exposure to red light, the PPy@MnO2-BSA(Ce6) nanoparticle could produce the cellular toxic reactive oxygen species (ROS, i.e., 1O2) to trigger the tumor PDT. Meanwhile, the nanoparticle could continuously catalyze H2O2 into endogenous oxygen, to not only relieve the hypoxia inside the tumor but also enhance the tumor PDT effect. The in vitro and in vivo experiments both affirmed the great potential of PPy@MnO2-BSA(Ce6) nanoparticle in MRI-guided combined PDT and PTT for tumor. This research lays a solid foundation for the theoretical design and clinical application of theranostic nanoprobe in the future.