Investigators at The Methodist Hospital Research Institute (Houston, TX, USA) created the highly efficient thermal transfer nanoparticles by confining gold nanoshells into nanopores of silicon microparticles. In the presence of infrared light at 808 nm, the gold-filled silicon particles heated up a surrounding aqueous solution by about 20 °C in seven minutes.

Hollow gold responds to near-infrared (NIR) light, which is able to penetrate deeply inside the body and which causes less damage to tissues compared to shorter wavelength light due to less absorbance by the tissue chromophores.

The investigators used human and mouse breast-cancer lines to test cell killing in vitro and the mouse model of 4T1 mammary tumor for in vivo studies. They reported in the January 3, 2012, online edition of the journal Advanced Healthcare Materials that the nanoparticles effectively killed cancer cells both in vitro and in the mouse model.

“Hollow gold nanoparticles can generate heat if they are hit with a near-infrared laser,” said first author Dr. Haifa Shen, assistant research member at The Methodist Hospital Research Institute. “Multiple investigators have tried to use gold nanoparticles for cancer treatment, but the efficiency has not been very good – they would need a lot of gold nanoparticles to treat a tumor. We found that heat generation was much more efficient when we loaded gold nanoparticles into porous silicon, the carrier of the multistage vectors.”

“The hollow gold particles we load into the porous silicon must be the right size and have the correct-sized space inside them to interact with the infrared light we are using,” said Dr. Shen. “But the wavelength of infrared we use will have to change depending on where the tumor is. If it is close to the skin, we can use shorter wavelengths. Deeper inside the body, we have to use longer wavelengths of infrared to penetrate the tissue. The hollow space of the gold particles must be modified in response to that. We are planning preclinical studies to study the technology's impact on whole tissues, breast cancer cells, and possibly pancreatic cancer cells. We would also like to see whether this approach makes chemotherapy more effective, meaning you could use less drugs to achieve the same degree of success in treating tumors. These investigations are next.”

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