Theranostic 2D ultrathin MnO2 nanosheets with fast responsibility to endogenous tumor microenvironment and exogenous NIR irradiation.

The fabrication of functional nanoparticles with unique ultra-sensitivity to endogenous tumor microenvironment (TME) is of great significance for their improved theranostic performance and easy excretion out of the body, which has not been realized among diverse nano-sized photothermal agents for photothermal therapy (PTT) of tumor. In this work, we report on the synthesis of 2D ultrathin MnO2 nanosheets for highly efficient PTT against tumor with ultra-sensitivity to endogenous TME. These ultrathin 2D MnO2 nanosheets show the intriguing characteristic of disintegration and releasing of Mn2+ in response to the mild acidic condition and elevated reducing microenvironment of TME, which has successfully realized the pH- and reducing-responsive T1-weighted magnetic resonance imaging of tumor. Importantly, the high PTT efficiency of 2D MnO2 nanosheets responsive to exogenous NIR irradiation has been systematically demonstrated both in vitro and in vivo for suppressing the tumor growth. This first report on the exploring of TME-sensitive photothermal agents with concurrent diagnostic and therapeutic (theranostic) functions significantly broadens the biomedical application of 2D functional biomaterials, which also promotes the further potential clinical translations of nano-sized photothermal agents.