A group under Professor Hongjie Dai at the Department of Chemistry at Stanford has created a laser-based treatment that destroys neoplastic cells but leaves healthy ones unharmed. The research results were published in the online edition of the Proceedings of the National Academy of Sciences (PNAS).
For the PNAS experiment, Dai and his colleagues used a basic tool of nanotechnology–carbon nanotubes, synthetic rods that are only half the width of a DNA molecule. Thousands of nanotubes could easily fit inside a typical cell.
“An interesting property of carbon nanotubes is that they absorb near-infrared light waves, which are slightly longer than visible rays of light and pass harmlessly through our cells,” Dai says. But shine a beam of near-infrared light on a carbon nanotube, and the results are dramatic. Electrons in the nanotube become excited and begin releasing excess energy in the form of heat.
In the experiment, Stanford researchers found that if they placed a solution of carbon nanotubes under a near-infrared laser beam, the solution would heat up to about 158 degrees F (70 C) in two minutes. When nanotubes were placed inside cells and radiated by the laser beam, the cells were quickly destroyed by the heat. However, cells without nanotubes showed no effects when placed under near-infrared light.
To assure that only diseased cells were destroyed in the experiment, the scientists had to find a way to selectively deliver carbon nanotubes into cancer cells and not into healthy ones. Dai and his co-workers achieved this by performing a bit of biochemical trickery. Unlike normal cells, the surface of a cancer cell contains numerous receptors for a vitamin known as folate. The researchers decided to coat the nanotubes with folate molecules, which would only be attracted to diseased cells with folate receptors.
The experiment worked as predicted. Most of the folate-coated nanotubes ended up inside cancer cells, bypassing the normal cells-like Trojan horses crossing the enemy line.