Hollow PtCo alloy nanospheres as a high-

Radiotherapy, as well as chemotherapy and surgery, occupies an essential position in tumor treatment. Nonetheless, insufficient radiation deposition and hypoxia-related radioresistance of cancer cells still are serious challenges in radiotherapy. Herein, we proposed a hollow PtCo nanosphere (PtCo NS)-based novel radiosensitizer with three advantages to sensitize tumor radiotherapy: (i) the high-Z element Pt ensured higher radiation absorption to cause more DNA damage, (ii) the platinum (Pt) and cobalt (Co) elements exhibited a dual catalase-like enzymatic activity to convert endogenic H2O2 to O2 efficiently, and (iii) the unique hollow nature of the PtCo NS provided a large specific surface area, which could amplify the catalytic reaction of H2O2 to induce reactive oxygen species and cancer cell apoptosis upon combination with radiation. Both in vivo and in vitro studies showed that the hollow PtCo NS could significantly inhibit tumor growth, simultaneously relieving tumor hypoxia with good biocompatibility and biosafety. This work presents a simple but multifunctional radiosensitizer with a unique hollow structure for radiotherapy enhancement.