Posted: September 5, 2006

Improving magnetic nanoparticle design

(Nanowerk News) Magnetic iron oxide nanoparticles have already proven their utility for imaging metastatic breast cancer lesions in sentinel lymph nodes, and numerous groups are attempting to use iron nanoparticles in other imaging applications. Researchers are also developing magnetic nanoparticles as miniature thermal scalpels for killing tumors as well as imaging them. These efforts stand to benefit from research described in three recent papers that detail new methods for designing and synthesizing iron-based, magnetic nanoparticles for biomedical applications.
Etienne Duguet, Ph.D., of the University of Bordeaux in France, has been leading an effort aimed at understanding the specific physical properties that a metal-based nanoparticle requires for optimal performance as a magnetic resonance imaging (MRI) agent or as an intracellular heat generator. Writing in the journal Progress in Solid State Chemistry ("Magnetic nanoparticle design for medical applications"), he and his collaborators outline these physical parameters and then detail the synthetic methods they used to control the size and chemical behavior of magnetic nanoparticles in order to satisfy these parameters.
The resulting particles, made of several layers of materials, can be modified to attach tumor-targeting molecules. The exact composition of the nanoparticles can also be varied in order to control the amount of heating that would result upon stimulation by a magnetic field. This ability could prove useful in designing nanoparticle heaters that would only get so hot before losing their magnetic properties – in essence, these nanoparticles would have a built-in on/off switch that would prevent overheating that could damage healthy tissue. The researchers demonstrated this ability by synthesizing a series of nanoparticles made of yttrium, iron and aluminum oxides with such on/off switches activated at temperatures over a 320°C range.
Meanwhile, Shouheng Sun, Ph.D., and his collaborators at Brown University have developed a one-pot method for creating iron oxide nanoparticles of all one size, rather than the typical output of particles with a range of diameters. The resulting nanoparticles comprise a metallic iron core surrounded by a crystalline iron oxide shell. This shell both stabilizes the nanoparticle and provides a place to attach tumor-targeting molecules. The investigators also developed a method for synthesizing a water-soluble version of these uniformly sized core-shell nanoparticles. The investigators published these methods in the Journal of the American Chemical Society ("Synthesis and Stabilization of Monodisperse Fe Nanoparticles").
In a third paper, published in the journal Current Applied Physics ("Surface-modified magnetite nanoparticles for hyperthermia: Preparation, characterization, and cytotoxicity studies"), a research team led by Yong-Keun Lee, Ph.D., of the Yonsei University in Seoul, South Korea, shows how surface modification of iron oxide nanoparticles alters their heat-generating capacity in response to a magnetic field. This study showed that coatings made of chitosan, a sugar-based polymer derived from shrimp and crab shells, markedly increased the heat generated by iron oxide nanoparticles when compared to other polymer coatings even though the nanoparticle core remained constant. The investigators also showed that chitosan-coated magnetic iron oxide nanoparticles were even less toxic than uncoated iron oxide nanoparticles, which are generally considered biocompatible.
Source: National Cancer Institute