Ultrasound-propelled Janus Au NR-mSiO2 nanomotor for NIR-II photoacoustic imaging guided sonodynamic-gas therapy of large tumors

Varieties of contrast agents have been developed for photoacoustic (PA) and ultrasound (US) imaging of cancers in vivo. However, access of traditional contrast agents into the sites of tumors has been principally through passive infiltration without any external force, preventing their deep penetration into the tissues of the tumors, and hindering the use of PA and US for deep tumor imaging. The concept of micro/nanomotors has been the focus of increasing attention as active theranostic agents due to their active movement in particular fluids, thereby conducting assigned tasks. Herein, US-propelled Janus mesoporous SiO2 partially coated gold nanorods (Au NR-mSiO2) were fabricated for deep tumor NIR-II PA imaging and synergistic sonodynamic-gas therapy. Following US irradiation, 2,2-azobis[2-(2-imidazolin-2-yl) propane] dihydrochloride (AIPH) loaded in mSiO2 (Au NR-mSiO2/AIPH) generated N2 microbubbles with high efficiency to achieve nanomotor drive. Due to the deep penetration of US, the nanomotors exhibited a capability to travel deep within sites of tumors, providing enhanced PA/US imaging inside the tumors. Furthermore, the nanomotor based cancer therapy was demonstrated through synergistic N2 gas and sonodynamic therapy. The US-propelled nanomotors demonstrated a novel strategy for the simultaneous PA/US dual imaging deep within tumor tissues and precise therapy of large tumors.