Porous silicon as an agent for cancer thermotherapy based on near-infrared light irradiation

In recent years, new thermotherapies based on nanoshells and more recently single-wall carbon nanotubes (SWCNTs) in combination with near-infrared (NIR) light irradiation have received significant attention as efficient techniques to destroy cancer cells selectively. Very recently we have reported that porous silicon (PSi) can also be utilized as a therapeutic agent that generates heat sufficient to kill cancer cells without toxicity upon exposure to NIR light. In this paper, we report the heat generation abilities of a PSi suspension, a PSi/NaCl suspension and a PSi/phosphate-buffered saline (PBS) suspension during continuous irradiation with NIR light and the in vitro cell test results obtained by using thermotherapy based on PSi and NIR light irradiation. The PSi/NaCl suspension showed heat generation ability superior to those of the PSi suspension and PSi/PBS suspension. The temperature of the PSi/NaCl suspension was elevated to 55 and 76 °C after 3 and 20 min NIR irradiation at 300 mW cm⁻², respectively, while that of the control was elevated to 31 and 39 °C after 3 and 20 min, respectively. In vitro cell test results suggest that thermotherapy based on PSi in combination with NIR light irradiation is an efficient technique to destroy cancer cells selectively without damaging the surrounding healthy cells and that heterochromatic NIR radiation can also be utilized successfully for this purpose.