Iron Carbide, Fe5C2, has long been used in metallic alloys and hard coatings for its superior resilience. Less known is that Fe5C2 also displays strong magnetism and good biocompatibility, making it a promising biomaterial with applications in fields like magnetic resonance imaging (MRI) and magnetic separation. However, these applications require Fe5C2 to be made in the form of colloidally stable nanoparticles, which has proven to be challenging. This problem was solved recently by UGA graduate student Wei Tang, and her advisor Dr. Jin Xie, along with their collaborators. The team used a high temperature decomposition method to prepare Fe5C2 nanoparticles. The as-prepared products are coated with hydrophobic alkyls and cannot be dispersed in water. For uses in bio-related applications, the researchers added a second, phospholipid coating onto the particle surface to render them water soluble. The resulting nanomaterials possess strong and stable magnetization in the air. Also, they showed low toxicity in cell toxicity studies. More impressively, the particles exhibit an r2 relaxivity—which is a measure of a material’s ability to induce contrast in MRI—of 464.02 mM-1s-1. This value is among the highest of all the MRI contrast probes reported so far. As a comparison, clinically used Fe3O4 nanoparticles have an r2 of ~100 mM-1s-1. Encouraged by the great physical properties, the group further evaluated the particles in small animal tumor models for tumor targeting and imaging. For that purpose, the particles were coupled to a tumor recognizing molecule. This grants the particles with the ability to selectively home to tumors from the circulation. Later, in vivo MRI studies confirmed the hypothesis: after systemic injection of Fe5C2 nanoparticles, the researchers observed significant signal changes in tumors on MR images. They also confirmed, by immunostaining, that the signal change was indeed caused by Fe5C2 nanoparticle accumulation in tumors. These observations strongly suggest the potential of Fe5C2 nanoparticles in MRI as well as other related fields. The story was recently published in Small as a research communication (DOI: 10.1002/smll.201303263).
