Protein-Directed Synthesis of γ-Fe 2 O 3 Nanoparticles Bull. Korean Chem. Soc. 2014, Vol. 35, No. 5 1375 http://dx.doi.org/10.5012/bkcs.2014.35.5.1375 Protein-Directed Synthesis of γ-Fe 2 O 3 Nanoparticles and Their Magnetic Properties Investigation Rouhollah Soleyman, * Ali Pourjavadi, †,* Nazila Masoud, † Akbar Varamesh, and Abolfazl Sattari ‡ Polymer Science and Technology Division, Research Institute of Petroleum Industry (RIPI), P.O. Box 14115-143, Tehran, Iran. * E-mail: soleymanr@ripi.ir † Polymer Research Laboratory, Department of Chemistry, Sharif University of Technology, Tehran, Iran * E-mail: purjavad@sharif.edu ‡ Chemical Science and Technology Research Division, Research Institute of Petroleum Industry (RIPI), Tehran 1485733111, Iran Received October 8, 2013, Accepted January 15, 2014 In this study, maghemite (γ-Fe 2 O 3 ) nanoparticles were produced using gelatin protein as an effective mediator. Size, shape, surface morphology and magnetic properties of the prepared γ-Fe 2 O 3 nanoparticles were characterized using XRD, FT-IR, TEM, SEM and VSM data. The effects of furnace temperature and time of heating together with the amount of gelatin on the produced gelatin-Fe 3 O 4 nanocomposite were examined to prove the fundamental effect of gelatin; both as a capping agent in the nanoscale synthesis and as the director of the spinel γ-Fe 2 O 3 synthesis among possible Fe 2 O 3 crystalline structures. Key Words : Nanostructures materials, Maghemite nanoparticles, Magnetic measurements Introduction In the last two decades, the use of magnetic nanoparticles in biomedical applications has had fast growth and during this explosive expansion, most interests in the clinical utilization of magnetic nanoparticles have focused on mag- hemite (γ-Fe 2 O 3 ) nanoparticles because of their chemical inactivity, non-toxicity, biocompatibility, biodegradability, low particle dimension, large surface area and suitable magnetic properties. 1-4 Due to its spinel structure with two magnetically nonequivalent interpenetrating sub lattices, maghemite shows excellent magnetic behavior which has been used in magnetic resonance imaging (MRI) contrast enhancement, 5,6 bio-magnetic separations, 7 hyperthermia treatment, 8 and magnetic drug targeting. 9,10 All these biomedical applications require nanoparticles with high magnetization values, sizes smaller than 100 nm, and narrow particle size distributions. Various methods have been reported for the synthesis of iron oxide nanoparticles via coprecipitation of Fe 2+ and Fe 3+ ions in alkaline medium, 11 using sonochemical synthesis, 12 microwave-hydrothermal, 13 and chemical solutions. 14 Moreover, some bio-scaffolds such as polysaccharide, 15 DNAs, 16 viruses, 17 proteins and peptides, 18-20 have been utilized in the synthesis of magnetic nanostructures. In this study, we have prepared maghemite (γ-Fe 2 O 3 ) nanoparticles after high temperature oxidation of gelatin- Fe 3 O 4 nanocomposite, obtained from Fe 3+ ions in alkaline medium in the presence of a protein (gelatin) as an effective capping agent. Overall, this method introduces a simple, soft and inexpensive procedure for synthesis of maghemite nano- particles with narrow size distribution and pure crystalline phase. Also, the effect of temperature, time of heating and the amount of gelatin on the synthesis has been investigated by the use of various techniques. Experimental Materials. Pure gelatin, iron (III) sulfate and hydrazine hydrate solution (N 2 H 4 ·H 2 O, 80 wt %) were purchased from Merck Co. (Darmstadt, Germany) and Double distilled water was used for synthesis of nanoparticles. Characterization. The powder particles were investigated by TEM (Modelno. CM120, Philips), XRD (D4 endeavor) (Cu Kα = 0.154 nm), and SEM (Modelno. S6100, Hitachi) for determining their shape, size and crystallinity. The inter- action of nano-particles with protein, and their behavior before/after elimination of gelatin was investigated using an ABB Bomem MB-100 FT-IR spectrophotometer. The mag- netic moment of the nanomaterials was measured using Lake Shore model 7400 vibrating sample magnetometer (VSM). X-ray photoelectron spectroscopy (XPS) graph was taken on a Thermo Electron Corporation spectrometer with an Al Kα (1486.6 eV) radiation. Synthesis of γ-Fe 2 O 3 Nanoparticles. The maghemite nanoparticles were obtained by hydrothermal treatment of Fe 2 (SO 4 ) 3 solution in the presence of gelatin. Typically, aqueous Fe 2 (SO 4 ) 3 solution (20 mL, 0.05 M) was stirred with different concentrations of gelatin solutions of same volumes (5 mL). After stirring for 5 min, 8 mL absolute ethanol was added to the above solution. Finally, 80 wt % hydrazine hydrate solution (N 2 H 4 ·H 2 O) (10 ml) was added drop wise with vigorous stirring. After 10 min stirring, the mixture was treated for 24 h at 100 o C, then protein was partially or completely eliminated at different furnace temperatures (400, 600 and 800 o C) and various times (0.5, 1