Size-regulated group separation of CoFe2O4 nanoparticles using centrifuge and their magnetic resonance contrast properties

Jongeun Kang,Hyunseung Lee,Kwan Soo Hong,Yong Taik Lim,Heejeong Jeong,Areum Yeom,Young-Nam Kim

doi:10.1186/1556-276x-8-376

Abstract

Magnetic nanoparticle (MNP)-based magnetic resonance imaging (MRI) contrast agents (CAs) have been the subject of extensive research over recent decades. The particle size of MNPs varies widely and is known to influence their physicochemical and pharmacokinetic properties. There are two commonly used methods for synthesizing MNPs, organometallic and aqueous solution coprecipitation. The former has the advantage of being able to control the particle size more effectively; however, the resulting particles require a hydrophilic coating in order to be rendered water soluble. The MNPs produced using the latter method are intrinsically water soluble, but they have a relatively wide particle size distribution. Size-controlled water-soluble MNPs have great potential as MRI CAs and in cell sorting and labeling applications. In the present study, we synthesized CoFe2O4 MNPs using an aqueous solution coprecipitation method. The MNPs were subsequently separated into four groups depending on size, by the use of centrifugation at different speeds. The crystal shapes and size distributions of the particles in the four groups were measured and confirmed by transmission electron microscopy and dynamic light scattering. Using X-ray diffraction analysis, the MNPs were found to have an inverse spinel structure. Four MNP groups with well-selected semi-Gaussian-like diameter distributions were obtained, with measured T2 relaxivities (r2) at 4.7 T and room temperature in the range of 60 to 300 mM−1s−1, depending on the particle size. This size regulation method has great promise for applications that require homogeneous-sized MNPs made by an aqueous solution coprecipitation method. Any group of the CoFe2O4 MNPs could be used as initial base cores of MRI T2 CAs, with almost unique T2 relaxivity owing to size regulation. The methodology reported here opens up many possibilities for biosensing applications and disease diagnosis.PACS75.75.Fk, 78.67.Bf, 61.46.Df

Highlights

Magnetic resonance imaging (MRI) is a powerful diagnostic modality for noninvasive in vivo imaging due to its high resolution, lack of exposure to radiation, superior soft tissue contrast, and large image window
The Magnetic nanoparticle (MNP) synthesized by the coprecipitation method were found to have an extremely broad size distribution [14]
A simple centrifugation technique was combined with a coprecipitation method in aqueous solution in order to obtain four groups of CoFe2O4 MNPs

Summary

Introduction

Magnetic resonance imaging (MRI) is a powerful diagnostic modality for noninvasive in vivo imaging due to its high resolution, lack of exposure to radiation, superior soft tissue contrast, and large image window. The particle size can be controlled [15]; the MNPs are only soluble in nonpolar and moderately polar organic solvents This brings about the requirement for hydrophilic and biocompatible polymer coating to make them soluble enough for in vivo uses [16,17,18]. Several reports are available regarding the size regulation of MNPs synthesized by coprecipitation, including a temperature-controlled coprecipitation method that requires specialized equipment and a piezoelectric nozzle method [20,21]. These processes are either highly complex or relatively ineffective owing to the requirement for a high level of control over parameters such as temperature during the synthesis. The piezoelectric nozzle method is more effective for controlling the size; this technique requires specialized equipment such as a piezoelectric transducer and a frequency amplifier

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