The main complexity in hyperthermia is generating and controlling the temperature distribution within tumor cells without damaging the normal tissue. Superparamagnetic iron oxide nanoparticles ͑SPIONs͒ with a diameter of 11 nm were prepared by controlled coprecipitation and coated with oleic acid to prevent agglomeration and flocculation in the solvent. In situ monitoring of the temperature increment was performed to interpret the microwave absorption rate of the SPION dispersed in appropriate host media ͑polar or nonpolar solvents͒ during microwave irradiation. This approach allowed for the prediction of heating mechanisms as a result of the excitation of unpaired electrons of iron, effects of coating agents, particle size, and volume fraction ͑͒. The conversion efficiency from microwave irradiation to thermal energy was predicted by applying the conservation of energy to a differential volume. The rates of heat loss and energy absorption were obtained by nonlinear fitting of the experimental data.
Neural stem cells isolated from an adult rat’s spinal cord were loaded with
superparamagnetic gold-coated monocrystalline iron oxide nanoparticles (Au-MION)
intended for use as contrast enhancers in magnetic resonance imaging (MRI). A
dose-dependent attenuation of MRI signals was observed for Au-MION down to
0.001 µg Fe/µl
and for nanoparticle-loaded clusters of only 20 cells. The labelled cells were infused into the
spinal cord of anaesthetized rats and tracked by MRI at 1 h, 48 h and 1 month post-injection.
Histological analysis revealed that MRI signals correlated well with gold-positive staining
of transplanted cells. The present results show that Au-MION exerts powerful
contrast-enhancing properties and may represent novel MRI labels for labelling and
tracking the transplanted cells in vivo.
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