Could Gold Cure Cancer?

By Amanda Bertsch

nanogold

These are all particles of gold in solution. The reason for their strange colors lies in the sizes of the particles. Photo credit http://www.sigmaaldrich.com/materials-science/nanomaterials/gold-nanoparticles.html.

Craftsmen in the Middle Ages were very fond of their stained glass. They would frequently mix new compounds into the molten glass to try to get better colors. They observed that the best way to get a rich red color was to use a gold chloride compound. Gold is a yellow metal, and chloride is a greenish-yellow gas. How was a combination of the two producing red?

The answer, surprisingly, lies in one of the newest and most complicated areas of medical research: nanotechnology.

Nanotechnology is the branch of technology dealing with the manipulation of objects less than 100 nanometers in length. A nanometer is one billionth of a meter; a piece of DNA is about 2 nanometers wide; a human hair is anywhere from 80,000 to 100,000 nanometers wide. Nanotechnology often involves engineering devices or particles on a molecular scale.

On such infinitesimal scales, the laws change. Many nanoscale projects straddle the border between the Newtonian world that we know and the world of quantum physics; changing the size of a particle can substantially change its properties. In this gray area, metals become superconductors, everyday compounds become mysterious, and gold is red.

The reason for the color change lies in a phenomena known as surface plasmon resonance. As light hits a nanoparticle, it interacts with free electrons around the particle. This results in an oscillating charge near the particle, which causes certain wavelengths to be reflected back. Depending on the size of the nanoparticle, this results in a red or purple color. The nanoparticles produced by heating the gold chloride solution used in stained glass are spheres about 25 nanometers in diameter, which have a red color.

We’ve been using nanoscale gold ever since. It can be found in most electronics. It has uses in microscopes, sensors, fuel cells, and printable inks. But it also has an interesting property: when modified slightly, nanogold can bind to cancerous cells but cannot bind to healthy cells. This is vital because a large problem in cancer treatment is targeting medicine to the specific cells that need to be killed.

Nanogold is now being used to image tumors with greater accuracy. When nanoscale gold is injected into an area, it clusters around tumor cells. Pinpointing the locations of nanoparticle clusters allows doctors to identify a more exact size for a tumor and to see clearly if it has begun to spread. This more accurate diagnosis leads to better, more personalized treatment, which is more likely to be effective.

In the future, scientists hope to replace chemotherapy, which kills large regions of cells with chemicals, with photothermal and X-ray therapies. These therapies involve gold nanoparticles binding to cancer cells (or, in some studies, bacterial cells). When laser pulses or X-ray waves of a correct wavelength are applied, these nanoparticles can superheat and kill the cancer or bacteria they are clustered around.

Another important possibility is that of targeted drug delivery. Nanoscale gold particles have a huge surface-area-to-volume ratio, so they can be coated with a number of drug treatments and anti-fouling chemicals. Since these particles can be engineered to only bind to cancer cells, they can deliver drugs directly and only to the cells that need to be killed, sparing the rest of the body and sidestepping most of the negative effects of chemotherapy.

Of course, more research is needed. Scientists are still investigating the potential effects of gold on the rest of the body—there’s a possibility that gold nanoparticles could accumulate in vacuoles, causing problems. And gold nanoparticles are expensive to manufacture and purchase; just 100 mL of the same 25 nanometer gold particles that are present in stained glass costs around $300 after production and purification costs. But it seems clear that wherever the fight against cancer leads, gold will play a substantial role in the treatments of tomorrow.

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