been mentioned alongside their syntheses, some unusual properties and applications call for special mention.
Individual magnetic nanoparticles, apart from displaying superparamagnetic
behavior, possess other unusual qualities. Bonet et al. [75] have shown that small
ferrite (in the magnetoplumbite structure) nanoparticles can have their magnetic
polarizations completely reversed through uniform rotation of their magnetization.
The spin precession of the whole particle magnetic moment of 4 nm g-Fe 2 O 3
nanoparticles has been monitored, using neutron scattering, by Lefmann et al.
[76]. These authors find that the precession is coherent since it is associated with
the excitation of ferrimagnetism in the nanoparticle.
Oxide nanoparticles, unlike nanoparticles of metals, display an expansion in
their lattice parameters in comparison with the bulk. Tsunekawa et al. have examined sub-10 nm CeO 2Àx and sub-100 nm BaTiO 3 nanoparticles using a combination of electron diffraction, X-ray photoelectron spectroscopy and ab initio computer simulations. They find that in the CeO 2Àx system, the lattice expansion
arises from a decrease in Ce valence, whilst in the BaTiO 3 system, the decreasing
TiaO covalency with decreasing particle size results in the expanded lattice.
There is continued interest in magnetic oxide nanoparticle assemblies for magnetic data storage. Recent advances in this area have come from the group of Sun,
who have prepared magnetite nanoparticles [77] from Fe(II) acetylacetonate in refluxing diphenyl ether in the presence of oleic acid and oleylamine. Precipitation
by addition of ethanol gave 4 nm Fe 3 O 4 nanoparticles which could be used to seed
the growth of larger Fe 3 O 4 particles (reaching 16 nm). The larger Fe 3 O 4 nanoparticles can be oxidized to g-Fe 2 O 3 with a distinct powder XRD pattern. The same
group [78] have then self-assembled these nanoparticles as well as performed coupled self-assemblies of Fe 3 O 4 nanoparticles with FeaPt nanoparticles and then
annealed the films to obtain exchange-coupled nanocomposite assemblies.
An interesting and novel application for magnetic nanoparticles is their use as
intracellular magnetic labels in nuclear magnetic esonance imaging. The presence
of magnetic nanoparticles results in protons in their vicinity relaxing at a much
faster rate. Since NMR imaging is based on the rate of magnetic relaxation, there is
distinct contrast introduced. Biocompatible dextran-coated nanoparticles have been
conjugated with peptides to improve their uptake into target cells. These have then
been found to significantly aid the NMR imaging of the cells [79]. Weissleder et al.
have also conjugated specific oligonucleotide sequences to magnetic oxide nanoparticles [80]. This results in their being able to employ NMR methods in the rapid
detection of DNA sequences that are complementary to the oligonucleotide that is
bound to the nanoparticle. In functional magnetic resonance imaging (fMRI) experiments, primates or humans are exposed to some external stimulus while their
brains are imaged. This technique has proved invaluable in mapping the brain, in
terms of associating region with function. Magnetic nanoparticles (dextran-coated
magnetite) have been used to enhance fMRI imaging contrast in the Rhesus brain
in experiments that measured photic response [81].
Magnetic oxide nanoparticles are also finding a number of other uses, including
in magnetic drug delivery and in hyperthermic cancer therapy. In the former, the
5.4 Prospects 109
Individual magnetic nanoparticles, apart from displaying superparamagnetic
behavior, possess other unusual qualities. Bonet et al. [75] have shown that small
ferrite (in the magnetoplumbite structure) nanoparticles can have their magnetic
polarizations completely reversed through uniform rotation of their magnetization.
The spin precession of the whole particle magnetic moment of 4 nm g-Fe 2 O 3
nanoparticles has been monitored, using neutron scattering, by Lefmann et al.
[76]. These authors find that the precession is coherent since it is associated with
the excitation of ferrimagnetism in the nanoparticle.
Oxide nanoparticles, unlike nanoparticles of metals, display an expansion in
their lattice parameters in comparison with the bulk. Tsunekawa et al. have examined sub-10 nm CeO 2Àx and sub-100 nm BaTiO 3 nanoparticles using a combination of electron diffraction, X-ray photoelectron spectroscopy and ab initio computer simulations. They find that in the CeO 2Àx system, the lattice expansion
arises from a decrease in Ce valence, whilst in the BaTiO 3 system, the decreasing
TiaO covalency with decreasing particle size results in the expanded lattice.
There is continued interest in magnetic oxide nanoparticle assemblies for magnetic data storage. Recent advances in this area have come from the group of Sun,
who have prepared magnetite nanoparticles [77] from Fe(II) acetylacetonate in refluxing diphenyl ether in the presence of oleic acid and oleylamine. Precipitation
by addition of ethanol gave 4 nm Fe 3 O 4 nanoparticles which could be used to seed
the growth of larger Fe 3 O 4 particles (reaching 16 nm). The larger Fe 3 O 4 nanoparticles can be oxidized to g-Fe 2 O 3 with a distinct powder XRD pattern. The same
group [78] have then self-assembled these nanoparticles as well as performed coupled self-assemblies of Fe 3 O 4 nanoparticles with FeaPt nanoparticles and then
annealed the films to obtain exchange-coupled nanocomposite assemblies.
An interesting and novel application for magnetic nanoparticles is their use as
intracellular magnetic labels in nuclear magnetic esonance imaging. The presence
of magnetic nanoparticles results in protons in their vicinity relaxing at a much
faster rate. Since NMR imaging is based on the rate of magnetic relaxation, there is
distinct contrast introduced. Biocompatible dextran-coated nanoparticles have been
conjugated with peptides to improve their uptake into target cells. These have then
been found to significantly aid the NMR imaging of the cells [79]. Weissleder et al.
have also conjugated specific oligonucleotide sequences to magnetic oxide nanoparticles [80]. This results in their being able to employ NMR methods in the rapid
detection of DNA sequences that are complementary to the oligonucleotide that is
bound to the nanoparticle. In functional magnetic resonance imaging (fMRI) experiments, primates or humans are exposed to some external stimulus while their
brains are imaged. This technique has proved invaluable in mapping the brain, in
terms of associating region with function. Magnetic nanoparticles (dextran-coated
magnetite) have been used to enhance fMRI imaging contrast in the Rhesus brain
in experiments that measured photic response [81].
Magnetic oxide nanoparticles are also finding a number of other uses, including
in magnetic drug delivery and in hyperthermic cancer therapy. In the former, the
5.4 Prospects 109