Local hypoxia in tumors results in undesirable impediments for the efficiencies of oxygen‐dependent chemical and photodynamic therapy (PDT). Herein, a versatile oxygen‐generating and pH‐responsive nanoplatform is developed by loading MnO2 nanodots onto the nanosystem that encapsulates g‐C3N4 and doxorubicin hydrochloride to overcome the hypoxia‐caused resistance in cancer therapy. The loaded MnO2 nanodots can react with endogenous acidic H2O2 to elevate the dissolved oxygen concentration, leading to considerably enhanced cancer therapy efficacy. As such, the as‐prepared nanoplatform with excellent dispersibility and satisfactory biocompatibility can sustainably increase the oxygen concentration and rapidly release the encapsulated drugs in acid H2O2 environment. In vitro cytotoxicity experiments show a higher therapy effect by the designed nanoplatform, when compared to therapy without MnO2 nanodots under hypoxia condition, or chemical and photodynamic therapy alone with the presence of MnO2 nanodots. In vivo experiments also demonstrate that 4T1 tumors can be very efficiently eliminated by the designed nanoplatform under light irradiation. These results highlight that the MnO2 nanodots‐based nanoplatform is promising for elevating the oxygen level in tumor microenvironments to overcome hypoxia limitations for high‐performance cancer therapy.

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Enzyme-like metal–organic frameworks (MOFs) are currently one type of starring material in the fields of artificial enzymes and analytical sensing. However, there has been little progress in making use of the MOF structures based on the catalytically active metal center with multiple valences. Herein, we report a mixed-valence Ce-MOF (Ce-BPyDC) that can exhibit both oxidase-like and peroxidase-like activities. Ce-BPyDC was synthesized by a facile hydrothermal method, which preserves the rare coexistence of Ce­(III) and Ce­(IV) in the MOF structure. The enzymatic studies demonstrated the enzyme-like activities of Ce-BPyDC follow the Michaelis–Menten kinetics and are strongly dependent on temperature, pH, and reaction time. Ce-BPyDC was also revealed to exert high catalytic activity that could transcend horseradish peroxidase and other MOF nanozymes, due to the redox-active Ce­(III)/Ce­(IV) cycles inside. Furthermore, the simple synthesis, high nanozyme activity, and great stability of Ce-BPyDC motivated us to establish a colorimetric biosensing platform using 3,3′,5,5′-tetramethylbenzidine as a color reagent. Adopting this strategy, we established a visual, sensitive, and selective colorimetric method for ascorbic acid (AA) detection, for which the linear interval and limit of detection were 1–20 and 0.28 μM, respectively. The successful AA detection in real juice samples implies the promising use of such mixed-valence MOF nanozymes in food and biomedical samples.

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