Glutathione and H2O2 consumption promoted photodynamic and chemotherapy based on biodegradable MnO2–Pt@Au25 nanosheets

•Consumption of excess intracellular GSH by MnO2 nanosheets reduces the consumption of 1O2 and enhances the PDT efficiency.•The reduction of Pt(IV) prodrugs to toxic Pt(II) by GSH improves the chemotherapy efficiency.•MnO2 nanosheets reduced by superfluous H2O2 generate a great amount of O2 for PDT.•The reduced Mn2+ can be employed as contrast agents for T1- and T2-weighted MRI.