MnO2 nanosheets anchored with polypyrrole nanoparticles as a multifunctional platform for combined photothermal/photodynamic therapy of tumors

Herein, PPy@MnO2 nanocomposites were first harvested by anchoring MnO2 nanosheets on polypyrrole (PPy) nanoparticles via an in situ redox reaction, then polyethylene glycol (PEG) modifier and methylene blue (MB) photosensitizer were linked through electrostatic interactions to obtain PPy@MnO2-PEG-MB nanoarchitectures. PPy nanoparticles ensure photothermal therapy (PTT) ability and MnO2 nanosheets ameliorate tumor hypoxia for enhanced photodynamic therapy (PDT). Therefore, a multifunctional nanotherapeutic system was constructed for the combined PTT/PDT of tumors. For extracellular photothermal properties, the optimal temperature elevation was 52.6 °C with 54.4% photothermal conversion efficiency. The extracellular PDT ability was measured by detecting 1O2 generation; more 1O2 was produced under acidic conditions in the presence of H2O2 (a simulated tumor microenvironment). The effective cellular uptake of the nanotherapeutic system in HeLa cells was observed by confocal laser scanning microscopy (CLSM). CLSM also indicated that more 1O2 was generated by the nanotherapeutic system as compared to free MB in HeLa cells, confirming the amelioration of tumor hypoxia by MnO2 nanosheets. MTT assays demonstrated that the nanotherapeutic system possessed superior biocompatibility without laser irradiation, and the lowest cell viabilities for single PTT and PDT groups were 13.78%, 38.82% respectively, while there was only 1.29% cell viability in the combined PTT and PDT group. These results suggest that the strategy of assembling PPy with MnO2 for a multifunctional PTT and enhanced PDT nanoplatform was realized, and opens up an unimpeded approach for integrating photothermal reduction materials with MnO2 for use in synergistic PTT and PDT.