Gold has fast become one of the most promising materials for building devices on a nanoscale level thanks to a number of favorable properties.  Among the applications of gold nanodevices is the use of gold particles to deliver drugs.  Gold nanoparticles range from small nanoclusters up to larger, more complex nanostructures.

MIT researchers used the latter to create one of the first examples of a two-drug delivery system.

Frequently, medical problems such as AIDS or cancer are best combated by a mix of drugs; however, drugs typically have different intervals they have to be taken on.  Thus, merely injecting a mix of nanoparticles coated in or containing drugs would not be sufficient.  A more complex delivery system was needed.

The MIT researchers decided to make use of an important property of gold nanoparticles.  Gold nanoparticles, based on their size and shape melt when exposed to certain wavelengths of infrared light.  In the case of drug-carrying hollow gold nanoparticles, the melting process can release drugs at specific locations in the body.

To implement a two drug delivery, researchers used two types of large hollow nanoparticles -- longer ones, which they nicknamed "nanobones", and shorter ones, which they nicknamed "nanocapsules".

The nanocapsules melted when exposed to 800 nm wavelength light.  The nanobones, left intact, then melt when the wavelength of the infrared light is turned up to 1100 nm.  The result is a system for delivering up to three or four drugs at independently controlled intervals.  States Andy Wijaya, graduate student in chemical engineering and lead author of the paper on the study, "Just by controlling the infrared wavelength, we can choose the release time (for each drug)."

Kimberly Hamad-Schifferli, assistant professor of biological and mechanical engineering who supervised the project, states, "With a lot of diseases, especially cancer and AIDS, you get a synergistic effect with more than one drug."

In the study the payload used was a strand of DNA.  The nanoparticles could be used for gene therapy, as they can pack hundreds of strands of DNA into a single particle.

The key to expanding the research to more drugs will be devising new nanostructures which will melt at different wavelengths.

The study on the work whose lead authors were Professor Hamad-Schifferli and Mr. Wijaya was published in the American Chemical Society journal Nano and can be found here.  Other authors on the paper include Stefan Schaffer and Ivan Pallares, who were National Science Foundation REU (Research Experiences for Undergraduates) summer students through the MIT Department of Biological Engineering in 2008.