Nanophotonics: Gold nanoparticles show promise for cancer treatment

A father and son research team has struck gold for the second time in an attempt to detect and kill cancer cells using lasers, gold nanoparticles, and the binding properties of cells.

Last year, Mostafa El-Sayed at the Georgia Institute of Technology (Atlanta, GA) and Ivan El-Sayed at the University of California-San Francisco demonstrated that gold nanospheres coated with a cancer antibody were very effective at binding to tumor cells. When bound to the gold, the cancer cells scattered light, allowing the researchers to distinguish the benign cells from the malignant ones. Because the nanoparticles absorbed the laser light more easily, only the coated malignant cells were destroyed while the healthy cells were spared.

Recently, the researchers discovered an even more effective and safer way to detect and kill cancer cells. By changing the shape of gold nanospheres into cylindrical gold nanorods, they could detect malignant tumors, such as breast cancer, hidden deeper under the skin, and selectively destroy them with lasers only half as powerful as before without harming healthy cells. Additionally, they could lower the response frequency from the visible to the near-IR spectrum.

Because near-IR lasers can penetrate deeper under the skin than lasers in the visible spectrum, they can reach tumors that are inaccessible to visible lasers. Most solid cancer is located under the tissues, out of the range of visible light.

The gold nanoparticles, which are 1/1000 the width of a human hair, are nontoxic and can be injected into the human body to detect and kill cancer in a noninvasive manner.

Many cancer cells have a protein, known as epidermal growth factor receptor (EFGR), all over their surface, while healthy cells typically do not express that protein as strongly. By conjugating, or binding, the gold nanorods to an antibody for EFGR the researchers were able to get the nanoparticles to attach themselves to the cancer cells.

In one study, the researchers incubated two malignant oral epithelial cell lines and one benign epithelial cell line with nanorods conjugated to anti-EFGR. The malignant lines were clearly identifiable under a simple optical microscope. After being exposed to a continuous sapphire laser in the near-IR spectrum, the malignant lines only required half the laser energy to kill them as did the healthy cells.

Because gold scatters light so strongly, the cancer cells sprayed with the gold nanoparticles were immediately visible, which is extremely advantageous for early detection and treatment.

“For laser phototherapy treatment of skin cancer or for diagnostic biopsies, the spheres are fine, but for phototherapy of cancer deep under the skin, one needs to use the nanorod treatment,” says Mostafa El-Sayed, director of the Laser Dyanamics Laboratory and Regents’ professor of chemistry at Georgia Tech.