A new method called “thermal ablation” has taken a significant step toward fulfilling its promise as an effective cancer treatment. The principle behind this method is simple, where nanoparticles are concentrated within the body of a tumor, and through external stimulus, the particles can produce sufficient heat to effectively cook the tumor from the inside, killing the cancerous cells in the process. In the first issue of Advanced Healthcare Materials, Professor Mauro Ferrari and coworkers have reported a nanostructure of silicon and gold which is shown to be 4 times as effective at killing cancer cells in cell culture experiments as gold nanoshells are alone.
One of the challenges in modern cancer treatment is that cancerous cells can undergo rapid mutations making it difficult to eradicate all of the cells in a cancerous growth with just one therapeutic agent. A promising solution to this issue is the carry out a general treatment which could target all cancerous cells, irrespective of mutation. In this work, a unique nanostructure was fabricated consisting of hollow gold nanoshells nested inside a porous silicon disk. A suspension of such nanostructures was then injected into mammary tumor growths in mice. The gold/silicon structures absorb light strongly in the near infrared wavelengths and thus could be activated from outside the body by using a laser operating in the infrared. This point is of key practical importance because the healthy tissue surrounding the tumor does not absorb strongly at these wavelengths, and is therefore unharmed by the application of the laser. The in vivo experiments showed a significant inhibition of tumor growth as a result of the treatment which is an encouraging sign for the further development of this type of therapy.
The authors also investigated the mechanism by which their new gold/silicon nanostructure shows such improved photo-response over the gold nanoshells alone. The gold nanoshells absorb light of sufficient energy to excite collective oscillations of the conduction band electrons, called plasmons. The absorption of this energy can then be dissipated as heat, which is utilized for to kill cancer cells for the purpose of this work. The porous silicon disks serve to concentrate the gold nanoshells within a close proximity of less than 1 micrometer, where they can electronically couple with one another and produce an enhanced, cooperative effect. Additionally, silicon has a thermal diffusivity of almost 6 times that of water, which further helps to promote heat transfer to the surrounding tissue. Together this constitutes a significant new advance in materials science which may provide a roadmap for the development of a new treatment for cancer.