Gold is rewriting the script

Jan 11 2005

Pen strokes of the rich and famous and remote-controlled drug delivery systems of the future have been given the golden treatment in a new technology being developed at the University of Melbourne.

The same technology, which involves miniscule gold particles only nanometres in size, has been used to create gold ink and to develop intelligent delivery systems that may have potential as drug carriers.

The research is being conducted by Federation Fellow Professor Frank Caruso, from the Centre for Nanoscience and Nanotechnology at the Department of Chemical and Biomolecular Engineering, and his research team in collaboration with Dr Trevor Smith from the School of Chemistry.

To develop the intelligent delivery systems, the researchers lined the walls of microscopic polymer ‘delivery-vehicle’ particles with gold nanoparticles.

Because laser light is absorbed by the gold nanoparticles, they found that by simply shining a laser on loaded delivery vehicles (i.e. particles filled with various contents, such as an enzyme or drug), the walls could be opened and the contents released.

The research was recently published in the journal Advanced Materials.

“By encasing biologically significant substances, such as drugs, within the gold nanoparticle-shelled delivery vehicles, release of the active materials can be remotely controlled by shining a laser on the gold nanoparticles, which then opens the particle walls,” Professor Caruso says.

Dr. Benno Radt, a postdoctoral fellow in Professor Caruso’s team who is working on developing the delivery systems, says “we have already successfully demonstrated the release of an encapsulated enzyme, which was achieved on demand with a single nanosecond laser pulse.

“Inducing release of the delivery vehicle contents is so fast, it is feasible that large areas of interest could be scanned quickly even with a relatively low-power, low-cost laser.

“Also, there is no risk that the laser energy will be significantly absorbed by biological structures such as bodily organs because the absorption of the gold-coated delivery vehicles in the near infrared light region is intentionally engineered in the wavelength regime for which light has a maximum penetration depth in tissue.”

Professor Caruso says that up to now, a common approach for drug release has been to use changes in the local environment at the site where drug delivery is needed such as pH, salt, temperature or enzyme concentrations.

“Our approach is different in that release can be triggered externally, making drug release on demand possible.”

Postgraduate student, Ms Alexandra Angelatos, who is also working on the project says, “In addition to drugs, these gold-coated vehicles could be used for the controlled delivery of a wide range of other substances including genes, pesticides, cosmetics and food stuffs.”

Professor Caruso, who was previously at Max Planck Institute (MPI) and his colleague Dr David Gittins (MPI) successfully devised a technique to suspend high concentrations of gold nanoparticles in water without them settling to the bottom or sticking together (called high colloidal stability). This gold nanoparticle technology forms the basis for the technique used in the delivery vehicles.

German-based company, Nanosolutions, recently purchased the license for the high-concentration gold nanoparticle technology and have used it to formulate a gold ink, called GOLD. When a person writes with the ink the water evaporates, leaving nothing but a gold script on the page. The ink, which is now available to buy, can be used in any standard fountain pen and is, among other things, water and light resistant.

Website for GOLD: http://www.sign-it-gold.com/flash.html

http://www.unimelb.edu.au/