Oxygen-Vacancy-Rich Piezoelectric BiO Nanosheets for Augmented Piezocatalytic, Sonothermal, and Enzymatic Therapies.

Piezocatalytic therapy is a new-emerging reactive oxygen species (ROS)-enabled therapeutic strategy that relies on built-in electric field and energy-band bending of piezoelectric materials activated by ultrasound (US) irradiation. Despite becoming a hot topic, material development and mechanism exploration are still underway. Herein, as-synthesized oxygen-vacancy-rich BiO nanosheets (NSs) demonstrate outstanding piezoelectric properties. Under US, a piezo-potential of 0.25 V for BiO NSs is sufficient to tilt the conduction band to be more negative than the redox potentials of O / O , O /H O , and H O / OH, which initiates a cascade reaction for ROS generation. Moreover, the BiO NSs exhibit peroxidase and oxidase-like activities to augment ROS production, especially in the H O -overexpressed tumor microenvironment. Density functional theory calculations show that the generated oxygen vacancies in BiO NSs are favorable for H O  adsorption and increasing the carrier density to produce ROS. Furthermore, the quick movement of electrons enables an excellent sonothermal effect, for example, rapid rise in temperature to nearly 65 °C upon US with low power (1.2 W cm ) and short time (96 s). Therefore, this system realizes a multimode synergistic combination of piezocatalytic, enzymatic, and sonothermal therapies, providing a new direction for defect engineering-optimized piezoelectric materials for tumor therapy.