Such magnetic nanoparticles are of interest for a host of applications, including medical imaging and drug delivery.

Although relatively uniform maghemite and magnetite nanoparticles have been synthesized recently by other groups, time-consuming size-selection procedures were necessary. Not so with the new method, according to Taeghwan Hyeon, an assistant professor of chemical engineering at Seoul National University.

Hyeon and his coworkers first prepare uniformly sized iron nanoparticles by decomposing Fe(CO)₅ in octyl ether in the presence of oleic acid (a stabilizing agent) at 100 ºC and then aging the iron oleate complex at 300 ºC. Next, the iron particles are oxidized to -Fe₂O₃ nanocrystallites (shown) using trimethylamine oxide [(CH₃)₃NO], a mild oxidant. By adjusting reaction parameters, the researchers can "tune" the size of the -Fe₂O₃ particles from 4 to 16 nm. Particles 13 nm in size can also be made in a single step using a variation of the procedure.

Hyeon foresees using the process to prepare multikilogram quantities of nanoparticles.

Chemist Christopher B. Murray's team at IBM Watson Research Center in Yorktown Heights, N.Y., has tried the new synthesis, and Murray says "it works beautifully." The high quality, crystallinity, and uniformity of the particles are "pretty compelling," he tells C&EN. Murray thinks the method "will be rapidly adopted as a new standard" for the preparation of -Fe₂O₃ nanoparticles.

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