Precise Design of TiO₂@CoO_x Heterostructure via Atomic Layer Deposition for Synergistic Sono-Chemodynamic Oncotherapy

Sonodynamic therapy (SDT), a tumor treatment modality with high tissue penetration and low side effects, is able to selectively kill tumor cells by producing cytotoxic reactive oxygen species (ROS) with ultrasound-triggered sonosensitizers. N-type inorganic semiconductor TiO₂ has low ROS quantum yields under ultrasound irradiation and inadequate anti-tumor activity. Herein, by using atomic layer deposition (ALD) to create a heterojunction between porous TiO₂ and CoO_x, the sonodynamic therapy efficiency of TiO₂ can be improved. Compared to conventional techniques, the high controllability of ALD allows for the delicate loading of CoO_x nanoparticles into TiO₂ pores, resulting in the precise tuning of the interfaces and energy band structures and ultimately optimal SDT properties. In addition, CoO_x exhibits a cascade of H₂O₂→O₂→·O₂⁻ in response to the tumor microenvironment, which not only mitigates hypoxia during the SDT process, but also contributes to the effect of chemodynamic therapy (CDT). Correspondingly, the synergistic CDT/SDT treatment is successful in inhibiting tumor growth. Thus, ALD provides new avenues for catalytic tumor therapy and other pharmaceutical applications.