Recipe for cooking a cancer cell: add 2 million nanorods, heat with laser

November 17, 2011
Gold Nanorods

Two million gold nanorods are taken up by each cancer cell, allowing for them to cook the cell (credit: Rice University)

Chemists at Rice University have found a way to load more than 2 million tiny gold particles called nanorods into a single cancer cell. The breakthrough could speed development of cancer treatments that would use nanorods like tiny heating elements to cook tumors from the inside.

The strategy is to deliver nontoxic particles that become deadly only when they are activated by a laser, according to study leader Eugene Zubarev, associate professor of chemistry at Rice. The nanorods, which are about the size of a small virus, can convert otherwise harmless light into heat.

“Ideally, you’d like to use a low-power laser to minimize the risks to healthy tissue, and the more particles you can load inside the cell, the lower you can set the power level and irradiation time,” said Zubarev, an investigator at Rice’s BioScience Research Collaborative (BRC).

Unfortunately, scientists who study gold nanorods have found it difficult to load large numbers of particles into living cells. Nanorods are pure gold, which means they won’t dissolve in solution unless they are combined with some kind of polymer or surfactant. The most commonly used of these is cetyltrimethylammonium bromide (CTAB), a soapy chemical often used in hair conditioner.

But CTAB is toxic, so the researchers replaced it with a closely related molecule called MTAB. Two additional atoms (sulfur and hydrogen) allow MTAB to form a permanent chemical bond with gold nanorods. (CTAB also binds more weakly to nanorods and has a tendency to leak into surrounding media from time to time, which is believed to be the underlying cause of CTAB-encased nanorod toxicity.)

Ref.: Leonid Vigderman, Dr. Pramit Manna, Prof. Eugene R. Zubarev, Quantitative Replacement of Cetyl Trimethylammonium Bromide by Cationic Thiol Ligands on the Surface of Gold Nanorods and Their Extremely Large Uptake by Cancer Cells, Angewandte Chemie International Edition, 2011; [DOI: 10.1002/anie.201107304]