International Journal of Pharmaceutics 439 (2012) 28–40 Contents lists available at SciVerse ScienceDirect International Journal of Pharmaceutics jo ur n al homep age: www.elsevier.com/locate/ijpharm Pharmaceutical Nanotechnology Long-term investigation on the phase stability, magnetic behavior, toxicity, and MRI characteristics of superparamagnetic Fe/Fe-oxide core/shell nanoparticles Afshin Masoudi a,∗ , Hamid Reza Madaah Hosseini a , Seyed Morteza Seyed Reyhani a , Mohammad Ali Shokrgozar b , Mohammad Ali Oghabian c,d , Reza Ahmadi a a Department of Materials Science and Engineering, Sharif University of Technology, Tehran, Iran b National Cell Bank, Pasteur Institute, Tehran, Iran c Department of Medical Physics and Biomedical Engineering, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran d Research Center for Science and Technology in Medicine, Imam Khomeini Hospital Complex, Tehran, Iran a r t i c l e i n f o Article history: Received 10 July 2012 Received in revised form 25 September 2012 Accepted 26 September 2012 Available online 8 October 2012 Keywords: Iron/iron oxide core/shell Chemical stability Magnetic behavior MRI contrast enhancement Cytotoxicity a b s t r a c t To efficiently enhance the contrast obtaining from magnetic resonance imaging (MRI), pharmaceuti- cal grade colloidal dispersions of PEG coated iron-based nanoparticles were prepared and compared to conventional pure iron oxide contrast agent. In this study, we synthesized ∼14 nm iron nanoparticles via NaBH 4 reduction of iron(III) chloride in an aqueous medium. The resulting nanoparticles were fur- ther oxidized by two different methods via (CH 3 ) 3 NO oxygen transferring agent and exposure to oxygen flow. XRD and electron microscopy analyses confirmed the formation of a second layer on the surface of -Fe core. As magnetic measurements and Mössbauer spectra of 4-months post prepared nanoparti- cles showed, 2.3 ± 0.5 nm amorphous oxide shell produced in oxygen flow could not protect the inner metallic iron from oxidation and resulting sample suffered from drastic change in its characteristics. However, (CH 3 ) 3 NO yielded nanoparticles with 3.6 ± 0.4 and 4.5 ± 0.7 nm crystalline oxide shells that retained their key properties even in long-term examinations. In addition, no significant difference was detected in cytotoxicity results of MTT assay test up to 4-months for core/shell nanoparticles, in com- parison with pure iron oxide sample, and all fall below 50% viability in the iron concentration of 400 g. In vitro MR signal reduction and corresponding relaxometry parameters, especially r 2 /r 1 > 2, assure that all nanoparticles can be administrated for negative contrast enhancement. Accumulation of core/shell nanoparticles in axillary and brachial lymph nodes of examined rats and minimum contrast enhance- ment of 20% regarding to pure iron oxide implies the efficiency of these materials as potential contrast agent. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Magnetic nanoparticles (MNPs) have attracted extensive atten- tion in many biomedical and bioengineering applications (LaConte et al., 2007; Medeiros et al., 2011; Park et al., 2012) due to the ability of manipulation or transportation of nanoparticles in an external magnetic field gradient (Bomatí Miguel et al., 2005). Stable aque- ous colloidal dispersions of superparamagnetic nanoparticles have been widely used as contrast enhancement agents in MR imaging (Schweiger et al., 2011; Masoudi et al., 2012). Because superpara- magnetic nanoparticles exert large enough magnetic moments, superior proton relaxation rates obtain in comparison with paramagnetic materials (Mansson and Børnerud, 2001) and sub- sequently images with enhanced contrast acquire. Owing to high ∗ Corresponding author. Tel.: +98 21 66005717; fax: +98 21 66005717. E-mail address: afshin masoudi@mehr.sharif.edu (A. Masoudi). magnetization value of iron (218 emu/g) that results in faster relax- ation times, exploiting this element in MRI contrast agents is quite beneficial (Hadjipanayis et al., 2008). Various experimental techniques for synthesis of iron nanopar- ticles are well established; thermal decomposition of organometal- lic precursors (Park et al., 2000; Farrell et al., 2003; Khalil et al., 2004; Cheong et al., 2012), microemulsion method (Wilcoxon and Provencio, 1999; Zhang et al., 2010; Wu et al., 2011), reduction of iron salts in aqueous solution (Yang et al., 2004; Diao and Yao, 2009; Singh et al., 2011), processes based on reaction with polyol (Justin Joseyphus et al., 2007), on inert gas condensation (Baker et al., 2004),or on laser pyrolysis (Dumitrache et al., 2005; Bomatí Miguel et al., 2007; Popovici et al., 2007). However, preparation of stable dispersion of iron is essentially restricted by high reactivity nature of iron with water and oxygen (Cheong et al., 2012). The con- sequence of reaction is an oxide layer constituting of Fe(II)/Fe(III) oxides in the vicinity of zero-valent iron core and Fe(III) oxide near the oxide/water interface (Signorini et al., 2003; Wang et al., 2009; 0378-5173/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijpharm.2012.09.050