Cancer-cell targeting and photoacoustic therapy using carbon nanotubes as "bomb" agents.

A unique approach using the large photoacoustic effect of single-walled carbon nanotubes (SWNTs) for targeting and selective destruction of cancer cells is demonstrated. SWNTs exhibit a large photoacoustic effect in suspension under the irradiation of a 1064-nm Q-switched millisecond pulsed laser and trigger a firecracker-like explosion at the nanoscale. By using such an explosion, a photoacoustic agent is developed by functionalizing the SWNTs with folate acid (FA) that can selectively bind to cancer cells overexpressing folate receptor on the surface of the cell membrane and kill them through SWNT explosion inside the cells under the excitation of millisecond pulsed laser. The uptake pathway of folate-conjugated SWNTs into cancer cells is investigated via fluorescence imaging and it is found that the FA-SWNTs can enter into cancer cells selectively with a high targeting capability of 17-28. Under the treatment of 1064-nm millisecond pulsed laser, 85% of cancer cells with SWNT uptake die within 20 s, while 90% of the normal cells remain alive due to the lack of SWNTs inside cells. Temperature changes during laser treatment are monitored and no temperature increases of more than +/- 3 degrees C are observed. With this approach, the laser power used for cancer killing is reduced 150-1500 times and the therapy efficiency is improved. The death mechanism of cancer cells caused by the photoacoustic explosion of SWNTs is also studied and discussed in detail. These discoveries provide a new way to use the photoacoustic properties of SWNTs for therapeutic applications.