Gold Nanorods Help Fight Cancer

A new study has shown how tiny nanorods made of gold can be triggered by a laser beam to blast holes in the membranes of tumor cells, setting in motion a complex biochemical mechanism that leads to a tumor cell's self-destruction.

Researchers at the Weldon School of Biomedical Engineering at Purdue University (West Lafayette, IN, USA) conducted experiments with tumor cells in laboratory cultures, and took advantage of the fact that tumor cell membranes often have an abnormally high number of receptor sites to capture molecules of folic acid (folate). The researchers then attached folate to gold nanorods, enabling them to target the receptors and attach themselves to the tumor cell membranes, from where they were eventually taken up into the cells.

The researchers found that by exposing the nanorods to laser-emitted near-infrared light while they were still on the membrane surface, the nanorods cause the formation of membrane blebs similar to severe blistering. The researchers discovered, however, that the blebbing was caused through a complex biochemical pathway, and not by the heat generated through the energy absorbed. Extra calcium enters the cell and triggers enzyme activity, which causes the infrastructure inside the cell to become loose, giving rise to the membrane blebs. The study was published in the October 19, 2007, edition of the journal Advanced Materials.

"We have found that rather than cooking the cells to death, the nanorods first punch holes in the membrane,” said co-author Alexander Wei, Ph.D., an associate professor of chemistry at Purdue. "This generates a plasma bubble that lasts for about a microsecond, in a process known as cavitation. Every cavitation event is like a tiny bomb. Then suddenly, you have a gaping hole where the nanorod was.”

The gold rods used were less than 15 nanometers wide and 50 nanometers long, or roughly 200 times smaller than a red blood cell. Their small size is critical for the technology's potential medical applications, since the human immune system quickly clears away particles larger than 100 nanometers, whereas smaller nanoparticles can remain in the bloodstream far longer.


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Weldon School of Biomedical Engineering