For our oncology applications we use a silica (i.e., glass) core surrounded by an ultra-thin gold shell.

The optical properties of AuroShell™ particles depends dramatically on the relative sizes of the core and the thickness of the metal shell. By varying the relative core size and shell thicknesses, the optical properties of AuroShell™ particles can be varied across a broad range of the electromagnetic spectrum that spans the visible and the infrared regions. For example, small gold particles generally will absorb light in the green section of the visible spectra. When this same material is used as the shell of an AuroShell™ particle, the particle can be manufactured to interact with near-infrared or other wavelengths, dramatically shifting the optical properties of the particle.

AuroShell™ particles can be made either to preferentially absorb or scatter light by varying the absolute size of the particle relative to the wavelength of the light at their optical resonance. For cancer applications, AuroShell™ particles designed to ABSORB near-infrared wavelengths are used. Metals convert absorbed light into heat with a high efficiency (to illustrate, metal surfaces exposed to sunlight become very hot in the summer sun). Thus, AuroShell™ particles become a very specific heat generator within a tumor, destroying a tumor from the inside.

The ability to "tune" AuroShell™ particles to a desired wavelength is critical to in vivo therapeutic applications. Human blood and tissue minimally absorb certain near-infrared wavelengths of light, enabling us to use an external laser to deliver light through tissue to AuroShell™ particles that have accumulated in a tumor.