Oxygen-Vacancy-Rich Piezoelectric BiO_2- _x Nanosheets for Augmented Piezocatalytic, Sonothermal, and Enzymatic Therapies.

Abstract

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_2- _x nanosheets (NSs) demonstrate outstanding piezoelectric properties. Under US, a piezo-potential of 0.25 V for BiO_2- _x NSs is sufficient to tilt the conduction band to be more negative than the redox potentials of O₂ /^• O₂ ^- , ^• O₂ ^- /H₂ O₂ , and H₂ O₂ /^• OH, which initiates a cascade reaction for ROS generation. Moreover, the BiO_2- _x NSs exhibit peroxidase and oxidase-like activities to augment ROS production, especially in the H₂ O₂ -overexpressed tumor microenvironment. Density functional theory calculations show that the generated oxygen vacancies in BiO_2- _x NSs are favorable for H₂ O₂  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^-2 ) 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.