Virginia Commonwealth University physicists, working with one of the most precious materials on Earth – gold -- and with one of the most common – sand -- have created a so-called “nano-bullet” that targets tumors and may help scientists develop non-invasive cancer treatments.
The scientists found that when gold particles are reduced to a few nano-meters -- just billionths of a meter -- they become highly reactive and readily bind to silica clusters, allowing the cluster to absorb infrared light and create enough heat to potentially kill cancer tumors. Silica is the main element in sand.
In the October 2004 issue of the American Physical Society journal Physical Review Letters, VCU researchers, led by Puru Jena, Ph.D., examined the electronic structure and bonding properties of gold and silica. They observed a dramatic change in the physical properties of both elements when their sizes were reduced to two or three nano-meters.
The scientists identified several defects and dangling bonds on the silicon atoms, which provide potential absorption sites for the gold atoms. The gold atoms readily accept electrons, and the new gold coating on the silicon atoms completely changes the charge distribution and electronic structure of the silica cluster. The gold coating on silica results in a significant change in the optical gap, which is a critical factor in determining how light is absorbed.
“We have shown that a cluster of only three silicon atoms and six oxygen atoms can bind at least three gold atoms,” wrote Jena, senior author of the article. “As a result, the optical gap of the cluster becomes greatly reduced to the point that it can absorb infrared radiation.
”Therefore, the cluster becomes hot, which in turn can destroy tumor cells,” Jena wrote.
Previous studies have tested gold-coated silica shells that were approximately 100 to 200 nanometers for the treatment of cancer tumors. In the VCU study, Jena and his team examined particles that were much smaller.
“The advantage of using smaller particles is that they can be inserted into any part of the human body and treat cancer cells in their infancy,” he said. “Historically, both gold and silica have been used in bio-materials. The biocompatibility of these materials at the nanoscale will be investigated,” he added.
“The next step in the research is to synthesize the tiny gold-coated silica clusters and measure their energy gap,” Jena said. “The measured energy gap will verify the accuracy of the theoretical prediction, and hence confirm the view that these clusters can absorb infrared radiation.”
Silica, which is one of the most abundant elements on Earth, has a wide range of applications in microelectronics, optical communications, and thin film technology. Gold, known for its resistance to corrosion, does not oxidize like other metals and it is chemically inert. However, gold particles become very reactive when they are reduced to a very small size.
Jena collaborated with Qiang Sun, Ph.D., and Qian Wang, Ph.D., both postdoctoral fellows in the VCU’s physics department.