Oxygen-Vacancy-Rich Piezoelectric BiO 2-x 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 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 ultrasound, 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 O 2 /·O 2 - , ·O 2 - / H 2 O 2 , and H 2 O 2 /·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 H 2 O 2 -overexpressed tumor microenvironment. Density functional theory calculations show that the generated oxygen vacancies in BiO 2-x NSs is favorable for H 2 O 2 adsorption and increasing the carrier density to produce ROS. Furthermore, the quick movement of electrons enables an excellent sonothermal effect, e.g., rapid rise in temperature to nearly 65°C upon ultrasound with low power (1.2 W/cm 2 ) and short time (96 s). Therefore, our 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. This article is protected by copyright. All rights reserved.