Effective cancer cell killing by hydrophobic nanovoid-enhanced cavitation under safe low-energy ultrasound.

β-Cyclodextrin (β-CD)-capped mesoporous silica nanoparticles with hydrophobic internal nanovoids were prepared and used for effective cancer cell killing in synergistic combination with low-energy ultrasound (≤1.0 W cm(-2) , 1 MHz). The water-dispersible nanoparticles with hydrophobic internal nanovoids can be taken up by cancer cells and subsequently evoke a remarkable cavitation effect under irradiation with mild low-energy ultrasound (≤1.0 W cm(-2) , 1 MHz). A significant cancer cell killing effect was observed in cancer cells and in a mouse xenograft tumor model treated with the nanoagents together with the low-energy ultrasound, showing a distinct dependence on the concentration of nanoagents and ultrasound intensity. By contrast, an antitumor effect was not observed when either low-energy ultrasound or nanoagents were applied alone. These findings are significant as the technique promises a safe, low-cost, and effective treatment for cancer therapy.