Microfabricated magnetic microparticles enable high contrast MRI agents

Introduction Chemically synthesized magnetic nanoparticles[1], dendrimers[2], and micrometer-sized particles of iron oxide (MPIOs)[3,4] are becoming increasingly popular as T2 * MRI contrast agents. Among them, the larger microparticles are proving useful for labeling single cells for in vivo imaging[5-7]. In particular, the large magnetic moments of MPIOs means that even individual particles can be detected[8] pointing to the possibility of MRI tracking of cells labeled with single particles. Towards such goals, techniques that can increase the fractional metal content of the particles, or that can use materials of higher magnetization than iron oxide, are desirable for increasing each particle’s signal without also increasing its size. Recently it has been demonstrated that top-down microfabrication of MRI contrast agents may enable novel agent properties[9]. Here we show that such top-down microfabrication techniques can also be used to micromachine magnetic microparticles of controlled composition with higher (and more consistent) magnetic moments than their more commonly available chemically synthesized counterparts.