Iron Oxide-Based Magnetic Nanoparticles Synthesized from THE Organic Solution Phase for Advanced Biological Imaging - Nanotechnology for Biomedical Imaging and Diagnostics - page 26

Structure

Fe 3 O 4

fIgure 2.1 The schematic illustration of representative IOMNPs summarized in this
chapter: size, composition, and structure-controllable hybrid IOMNPs including dumbbell,
core-shell, and multilayer core-shell NPs.

derivative [7]. The polymer passivates and stabilizes the IOMNPs against aggregation
in the aqueous media. However, these IOMNPs produced via the coprecipitation of
Fe(II) and Fe(III) in a basic solution at low temperature show a low contrast effect in
clinical MRI applications due to their large size distribution and poor magnetic prop-
erties. Recently, IOMNPs were successfully synthesized in organic solution phases
with great control in size, crystallinity, composition, structure, and magnetic prop-
erties [8-10]. They become promising new-generation contrast agents for biomedical
imaging applications. In this chapter, we focus on the controlled synthesis of IOMNPs
and their hybrid NPs via this organic solution phase method and their use as advanced
MRI contrast agents. The main types of IOMNPs described in this chapter are shown
in Figure 2.1.

2.2 nanoMagnetIsM and MrI

MNPs have a unique size-dependent magnetism. With the decrease of physical size
from bulk form to nanoregime, an MNP shows a transition from multidomain structure
to single-domain structure within which all free spins are ferromagnetic coupled into
one direction [11, 12]. The critical size for the formation of single-domain particles is
determined by the innate magnetic anisotropy energy of the material and usually falls
in the range of tens of nanometers [12-14]. an IOMNP of less than 100 nm contains
one single-domain structure. For a group of single-domain IOMNPs, their overall
magnetization ( M ) reaches saturation ( M s ) when their magnetization directions are
aligned parallel under a large enough external magnetic field ( H ). The resistance to the
magnetization alignment is measured by susceptibility ( M / H ). Similar to bulk ferro-
magnets, these magnetized NPs can retain some collective remnant magnetization