VCU scientists studying a magnetic nanoparticle based on metallic iron for medical and communication applications

By Sathya Achia Abraham

Virginia Commonwealth University chemists working with iron have created for the first time an air-stable, magnetic nanoparticle with core-shell structure, which may advance applications in wireless communications, power electronics and targeted drug delivery.

The results also could lead to advances in power electronics and magnetic imaging and could improve the efficiency of electrochemical or catalytic reactions.

In the July issue of the Journal of Nanoscience and Nanotechnology, researchers reported the successful synthesis of a magnetic nanoparticle based on metallic iron that resisted oxidation using the reverse micelle technique with a doped iron oxide shell creating a core-shell enhanced ferrite. The researchers showed that nickel zinc ferrite — a non-native iron oxide — could be grown on the iron nanoparticles and remain air stable. Previous work by other groups has indicated that it is easy to get the surface of iron to rust to make a native iron oxide, however, the focus of this paper was on growing a non-native shell material.

“The reverse micelle method was employed here to produce nanoparticle ferrites as well as air stable metallic iron nanoparticles — a long-standing goal of nanoparticle magnetism,” said corresponding author of the paper Everett E. Carpenter, Ph.D., an assistant professor of chemistry at VCU. “We are now able to tailor a ferrites’ magnetic response by tailoring the core-shell structure.”

The reverse micelle technique is a unique chemical reaction system, which was critical in the synthesis of the iron-based nanoparticle. This technique provided the greatest flexibility and control over the size, size distribution, crystallinity and magnetic properties.

Iron is known for its important magnetic properties; however it is very reactive and this reactivity is further enhanced on the nano-level. According to Carpenter, some metals and alloys are easily synthesized at micron level or smaller sizes, but others resist this manipulation. There are several reasons for this, but in the case of iron the primary problem is that it oxidizes rapidly when exposed to air. This oxidation can be so rapid that it may cause iron to ignite and spontaneously combust.

“For use in practical applications, the synthesis of iron nanoparticles requires the stabilization of the iron core by a protective layer preventing oxygen from diffusing into the core,” Carpenter said. “Therefore, we utilized a novel core-shell approach toward enhanced ferrites where an iron core is encapsulated in a ferrite shell. This allows the iron to be protected while protecting or retaining the electronic properties of the ferrite.”
For decades, many disciplines, including biology, physics, chemistry and engineering, have been pursuing a wide variety of methodologies for producing nanomaterials. The research team compared the quality of their nanoparticles with those of other groups in the scientific literature. “By comparing our work materials with these other groups, we were able to explain this ambiguity and create a nanoparticle with more consistent and superior magnetic properties,” he said.

Carpenter and his colleagues also examined the importance of various reaction conditions and the corresponding effects on the magnetic properties and particle structure. Specific characteristics of iron, including the crystal structure and cation occupancies of the nanoparticle also were also considered.

“One of the convergences for biology, physics and chemistry revolves around magnetic materials,” Carpenter said. The new material can be used to create a smaller radar signal for military aircrafts or expand bandwidth for military and civilian communications; as biosensors; or in the biomedical field in target drug delivery and for magnetic imaging.

Researchers have already been able to apply their novel processes and technique in a pilot plant setting and have produced the same material on a large scale. Several patents are pending based on this work, which is a culmination of research that started at the Naval Research Laboratory where Carpenter was a research scientist for four years before joining VCU.

Carpenter and his colleagues are now studying how to appropriately ‘package’ the new material so that it can be successfully applied in the fields of biology, physics and chemistry.

This research was supported by grants from the Office of Naval Research, and the Defense Advanced Research Projects Agency (DARPA) Metamaterials program.

Carpenter collaborated with Shannon A. Morrison, a post-doctoral researcher at VCU; Christopher L. Cahill, with George Washington University in Washington, D.C.; Scott Calvin with Sarah Lawrence College in Bronxville, N.Y.; and Vincent G. Harris from Northeastern University in Boston, Mass.