Hollow gold and silver nanospheres developed by researchers at the University of  California, Santa Cruz, has shown some promise in treating lethal cancers, such as malignant melanoma.

Laser-inducted phototherapy is a new therapeutic use of electromagnetic radiation for cancer treatment. The use of targeted gold nanospheres may decrease the amount of laser energy needed to destroy tumor cells while also minimizing potential damage to surrounding normal, healthy tissue.

However, the ability for targeted delivery of the current used gold nanoparticles to tumor cells is currently limited. The answers may be found in a new class of photothermal coupling agents based on hollow gold nanoshells or nanospheres.

The hollow gold nanospheres developed in the laboratory of Jin Zhang, a professor of chemistry and biochemistry at UCSC have a unique set of attributes, including strong, narrow and tunable absorption of light.  The thickness of the gold shell may also be changed by carefully controlling the addition of gold salt.

Meanwhile, Zhang is working with researchers at the University of Texas M.D. Anderson Cancer Center, who have reported good results from preclinical studies conducted earlier this year, using the hollow gold nanostructures to target tumors for photothermal cancer therapy.

What makes this structure special is the combination of the spherical shape, the small size, and the strong absorption in visible and near infrared light, Zhang said. The absorption is not only strong, but it is also narrow and tunable. All of these properties are important for cancer treatment.'

Zhang presented his findings Sunday in Salt Lake City at the annual meeting of the American Chemical Society.

The hollow particles can be made in sizes ranging from 20 to 70 nanometers in diameter, which is considered ideal for biological applications that require particles to be incorporated into living cells.

Researchers at the M.D. Anderson Cancer  Center injected the nanospheres into mice with melanoma, which helped irradiate the animals' tumors with near-infrared laser light, heating the gold nanospheres and selectively killing the cancer cells to which the particles were bound.

The heat that kills the cancer cells depends on light absorption by the metal nanoparticles, so more efficient absorption of the light is better, Zhang explained. The hollow gold nanospheres were 50 times more effective than solid gold nanoparticles for light absorption in near-infrared.

One of Zhang's graduate students, Tammy Olsen, has designed hollow double nanoshell structures of gold and silver, which show enhanced SERS activities when compared to the hollow gold nanospheres.  SERS is a powerful optical technique that can be used for sensitive detection of biological molecules and other applications.

For further information on the hollow gold nanospheres, go to www.ucsc.edu/news_events/text.asp?pid=2790.