Mossbauer studies of nano-size controlled iron oxide for biomedical applications

Synthesis of iron oxide nanoparticles and correct characterizations by Mossbauer spectroscopy and transmission electron microscope (TEM) are reported. Mossbauer studies are essential tool because the only X-ray diffractometer (XRD) patterns in nanoparticles could not distinguish iron oxides from magnetite, maghemite, and spinel oxides because of similar crystal structure. MFe₂O₄ (M = Fe, Co) with spinel structure are made by reaction of iron(III) acetylacetonate [Fe(acac)₃] with surfactants at high temperature. We have used the phenyl ether, benzyl ether, and 1,2-hexadecanediol as solvents. Fe(acac)₃ was mixed in phenyl ether and benzyl ether for synthesis of the magnetite (Fe₃O₄). As boiling point of phenyl ether (259 °C) is lower than that of benzyl ether (298 °C), the size of magnetite nanoparticles can be controlled. And then, iron oxide nanoparticles have been coated by tetraethyl orthosilicate (TEOS) mixed ethyl alcohol and NH₄OH. The average particle sizes of iron oxides were 6, 13, and 18 nm, narrow size distribution was convinced by TEM. The Mossbauer spectrum for the 6 nm sample at room temperature displays a superparamagnetic behavior as demonstrated by the single quadrupole doublet with zero hyperfine fields. While 13 and 18 nm particle show partially superparamagnetic behavior at room temperature. It is concluded that 13 nm and 18 nm samples are maghemite and magnetite, respectively, from the Mossbauer spectra. It is suggested that 6 nm samples are available for biomedical applications such as hyperthermia and drug delivery system as a magnetic fluid carrier.