2 research outputs found
Effect of Surface Modification on Magnetization of Iron Oxide Nanoparticle Colloids
Magnetic iron oxide nanoparticles have numerous applications
in
the biomedical field, some more mature, such as contrast agents in
magnetic resonance imaging (MRI), and some emerging, such as heating
agents in hyperthermia for cancer therapy. In all of these applications,
the magnetic particles are coated with surfactants and polymers to
enhance biocompatibility, prevent agglomeration, and add functionality.
However, the coatings may interact with the surface atoms of the magnetic
core and form a magnetically disordered layer, reducing the total
amount of the magnetic phase, which is the key parameter in many applications.
In the current study, amine and carboxyl functionalized and bare iron
oxide nanoparticles, all suspended in water, were purchased and characterized.
The presence of the coatings in commercial samples was verified with
X-ray photoelectron spectroscopy (XPS). The class of iron oxide (magnetite)
was verified via Raman spectroscopy and X-ray diffraction. In addition
to these, in-house prepared iron oxide nanoparticles coated with oleic
acid and suspended in heptane and hexane were also investigated. The
saturation magnetization obtained from vibrating sample magnetometry
(VSM) measurements was used to determine the effective concentration
of magnetic phase in all samples. The Tiron chelation test was then
utilized to check the real concentration of the iron oxide in the
suspension. The difference between the concentration results from
VSM and the Tiron test confirmed the reduction of magnetic phase of
magnetic core in the presence of coatings and different suspension
media. For the biocompatible coatings, the largest reduction was experienced
by amine particles, where the ratio of the effective weight of magnetic
phase reported to the real weight was 0.5. Carboxyl-coated samples
experienced smaller reduction with a ratio of 0.64. Uncoated sample
also exhibits a reduction with a ratio of 0.6. Oleic acid covered
samples show a solvent-depended reduction with a ratio of 0.5 in heptane
and 0.4 in hexane. The corresponding effective thickness of the nonmagnetic
layer between magnetic core and surface coating was calculated by
fitting experimentally measured magnetization to the modified Langevin
equation
A Bioinspired Coprecipitation Method for the Controlled Synthesis of Magnetite Nanoparticles
Nature often uses precursor phases
for the controlled development
of crystalline materials with well-defined morphologies and unusual
properties. Mimicking such a strategy in in vitro model systems would
potentially lead to the water-based, room-temperature synthesis of
superior materials. In the case of magnetite (Fe<sub>3</sub>O<sub>4</sub>), which in biology generally is formed through a ferrihydrite
precursor, such approaches have remained largely unexplored. Here
we report on a simple protocol that involves the slow coprecipitation
of Fe<sup>III</sup>/Fe<sup>II</sup> salts through ammonia diffusion,
during which ferrihydrite precipitates first at low pH values and
is converted to magnetite at high pH values. Direct coprecipitation
often leads to small crystals with superparamagnetic properties. Conversely,
in this approach, the crystallization kineticsand thereby
the resulting crystal sizescan be controlled through the NH<sub>3</sub> influx and the Fe concentration, which results in single
crystals with sizes well in the ferrimagnetic domain. Moreover, this
strategy provides a convenient platform for the screening of organic
additives as nucleation and growth controllers, which we demonstrate
for the biologically derived M6A peptide