Development of Iron Nanoparticles for Magnetic Particle Imaging Applications

An investigation in creating highly magnetic and optimally sized iron nanoparticles for magnetic particle imaging (MPI) was performed. MPI is a noninvasive imaging technique that has gained much attention due to its high sensitivity, spatial resolution, and real time 3D imaging modality. The signal generated for MPI is highly dependent on the magnetic moment produced by magnetic nanoparticle tracers, which is related to the composition and size of the nanoparticles. Currently 25-30 nm sized iron oxide nanoparticles are the standard tracers used for MPI, however, further improvement of such tracers can be achieved by developing nanoparticles that contain pure iron. Therefore, various synthetic methods were investigated in order to determine optimal synthetic conditions for creating Fe nanoparticles around 20 nm in diameter.

Three series of iron nanoparticle syntheses were explored. Series 1 tested the effects various alkyl chained surfactant have on nanoparticle shape and size. From the first series, 20 nm sized iron core-shell structured particles were obtained. It was found that longer alkyl chained surfactants allowed for larger particle sizes due to an increase in steric hindrances to prevent agglomerations from forming during growth.

Series 2 tested a continuous injection of iron pentacarbonyl using an extended LaMer growth mechanism of nanoparticles. Different injection speeds and different surfactants were tested to determine potential changes in size and shape of the nanoparticles through this growth mechanism. From this series, it was found that lower injection speeds using hexadecylamine or octadecylamine as surfactants could produce larger iron nanoparticles.

Finally, series 3 investigated a solid-solid reduction synthesis to create iron nanoparticles. Iron oxide nanoparticles were synthesized through a thermal decomposition of iron (III) acetylacetonate and coated with silica. The uncoated and silica coated iron oxide nanoparticles were further reduced with calcium hydride to produce iron nanoparticles.

Characterization methods include Mössbauer spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), cytotoxicity tests, and preliminary MPI measurements.