Oxygen-Vacancy-Rich Piezoelectric BiO2- 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 BiO2- x nanosheets (NSs) demonstrate outstanding piezoelectric properties. Under US, a piezo-potential of 0.25V for BiO2- 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 BiO2- 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 BiO2- 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 (1.2Wcm-2 ) and short time (96s). 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.