Synthesis and Characterization of Oleic Acid Stabilized Monodisperse Magnetite Nanocrystals for Magnetic Resonance Imaging Applications

Abstract

Oleic acid stabilized magnetite nanocrystals have been synthesized by the organic phase thermal decomposition of iron oleate complex in 1-octadecene for potential application as magnetic resonance imaging (MRI) contrast agent. The synthetic process resulted in 13.5 and 15.1 nm highly monodisperse nanocrystals as revealed by transmission electron microscopy. Proton nuclear magnetic resonance (¹HNMR) spectroscopy and Fourier-transformed infrared spectroscopy results confirm that the nanocrystals are free from 1-octadecene, and that the oleic acid is chemisorbed on the nanocrystals which are critical for their safety and long term stability, respectively. X-ray powder diffractometry of the nanocrystals strongly suggest magnetite nanocrystalline phase. The magnetic properties of the nanocrystals were examined by superconducting quantum interference device magnetometer. The results indicate the superparamagnetic properties of the nanocrystals at room temperature and their large saturation magnetizations. ¹H-NMR relaxometry measurements demonstrate large longitudinal (r₁) and transverse (r₂) relaxivities of 32.6 and 96.3 mM^-1s^-1, respectively for 15.1 nm nanocrystals with r₂/r₁ relaxivity ratio of ~ 3.0 at 37 oC demonstrating their potential as promising MRI contrast agents.

Keywords: magnetite, nanocrystals, superparamagnetic, relaxometry, magnetic resonance imaging