We explored the catalytic activity and magnetic resonance imaging (MRI) capacity of Cu-doped ultrasmall
iron oxides with different doping ratios. Then, we screened a highly efficient ultrasmall active catalyst (UAC). Subsequently, a biodegradable magnetic nanoliposome was developed for multimodal
cancer theranostics through pH-sensitive
liposome coating of these UACs. Upon entering the body, the magnetic nanoliposomes significantly prolonged the metabolic time of UACs and promoted their accumulation in
tumors. Then, the strong photothermal (PT) effect of the magnetic nanoliposome quickly ablated the
tumor, showing promising PT
therapy. Upon entering
tumor cells, the magnetic nanoliposome rapidly degraded into many UACs and released chemotherapeutic drugs, contributing to
chemotherapy. In addition, UACs not only catalyzed Fenton-type reaction to produce excessive
reactive oxygen species (ROS) but also inhibited the synthesis of endogenous GSH by inactivating glutamyl
cysteine ligase, contributing to
cancer ferroptosis. Furthermore, the assembly-dissociation process of UACs showed the function of magnetic relaxation switches, significantly enhancing
tumor MRI signal change, achieving a more accurate diagnosis of the
tumor. Therefore, this magnetic nanoliposome splits into many UACs upon drug release and regulates the tumor microenvironment to overproduce ROS for enhanced synergistic
tumor theranostics, which provides a strategy for developing next-generation magnetic catalysts with biodegradability and multimodal antitumor
theranostics.