(567c) Gold-Coated Iron-Oxide Nanoparticles for Optical Imaging and Hyperthermia of Cancer

Fe₃O₄ nanoparticles are effective heat guides for minimally invasive cancer hyperthermia using an alternating electromagnetic (AEM) field. Conjugation of cancer-specific targeting molecules to the nano-sized particles allows cancer-specific treatment, with minimal damage to normal tissue.

Nano-scale, gold surfaces have a plasmon field that can be beneficially used to manipulate the fluorescence intensity of fluorophores for molecular imaging. When the fluorophore is at an appropriate distance from a nano-scale gold surface, the fluorescence intensity can be greatly enhanced. This distance for enhancement (in our previous studies, 5 - 10 nm) can be established by placing a spacer between the fluorophore and the gold surface. This fluorescence enhancement can increase the signal-to-noise ratio, and therefore the sensitivity of optical imaging.

Here, we are combining the magnetic properties of Fe₃O₄ nanoparticles and the plasmon field of nano-gold surfaces into a single nano-entity. When a fluorophore is linked to this entity, the resulting product is a highly fluorescent contrast agent for optical detection of a tumor and heat guide to the tumor. In order to achieve this goal, gold-coated Fe₃O₄ nanoparticles were synthesized. Fluorophores were then conjugated onto the particle via bio-compatible spacers. The entire entity was designed to have a total size of 10 ? 50 nm for efficient cell uptake. The level of heat generation under an AEM field was correlated to the Fe₃O₄ core size and gold shell thickness. The fluorescence intensity of the entity was studied with changes in the particle size and gold shell thickness.

The resulting single nano-entity can be used for both highly sensitive optical detection and hyperthermic treatment of cancer. The particles can also be used, without further modification, as contrast agents for MRI. Recently gold nanoparticles have been found to provide contrast for x-rays, and the entity may be used for x-ray/CT imaging as well.