Gold Nanocages as Optical Imaging Contrast Agents
Nanoscale cages and disease treatment
Nanoscale cages constructed of gold atoms can be tuned to interact with light in such a manner that they can be used to image molecular events in live cells and tissues using a technique known as optical coherence tomography (OCT). The gold nanocages, some 40 nanometers in diameter, were made by replacing the silver atoms in more easily constructed silver nanotubes . An international research team, led by Xingde Li, Ph.D., and Younan Xia, Ph.D., at the University of Washington, reported this work in the journal Nano Letters.
The gold nanocages owe their optical properties to plasmons, ripples of waves in the ocean of electrons flowing across the surface of metallic nanostructures. The type of plasmon that exists on a surface of a nanoscale object is directly related to its geometric structure, in this case the precise positioning of gold atoms in the nanocages. When light of a specific frequency strikes a plasmon that oscillates at a compatible frequency, the energy from the light is harvested by the plasmon, converted back to photons again (i.e., scattering) or phonons/thermal energy (i.e., absorption).
After constructing the nanocages and tuning their optical properties, this team attached monoclonal antibodies to some of the gold atoms. These antibodies recognize the breast cancer marker HER2, and the resulting targeted nanocages were then used to image breast cancer cells using OCT. In future experiments, the researchers will see if they can excite the nanocages with enough energy to turn them into miniature thermal scalpels that may be capable of killing targeted cancer cells.
This work was funded in part by the National Institutes of Health.