Iron oxide nanoparticles for biomedical applications
Date
2020
Authors
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Publisher
University of Delaware
Abstract
The research in this dissertation has been focused on the synthesis of iron oxide nanoparticles and their nanoclusters, the characterization of their magnetic and structural properties and their hyperthermia response for biomedical applications. The aim was to enhance the heating efficiency of nanoparticles using different methodologies such as changing the particle size and shape anisotropy, as well as increasing the dipolar interactions by nanoparticle clustering. ☐ A step by step synthesis method was used to form iron oxide nanoparticles while particle size and composition were controlled by varying the reaction parameters during synthesis. The appearance of Verwey transition in nanoparticles along with Mossbauer results, confirmed the presence of Fe3O4 phase in these samples. The as-made nanoparticles were in the superparamagnetic regime and increasing their size increased the blocking temperatures and enhanced their magnetic properties. Magnetic hyperthermia measurements showed that the heating efficiency of nanoparticles was enhanced by increasing their size. ☐ A general method for making nanoparticle clusters (NPCs) has been developed by using Cetrimonium Bromide (CTAB) and an oil in water emulsion system. The size of the clusters was precisely controlled by changing the CTAB concentration, the time of sonication and the heating temperature. Two types of clusters were made from two different sizes of primary individual nanoparticles and the structural and magnetic properties of them were measured. The shift of blocking temperature toward higher temperature confirmed the larger magnetic dipole-dipole interactions present in the case of clusters. Ac susceptibility studies over a range of temperatures showed two peaks, with the higher temperature peak corresponding to weakly interacting magnetic nanoparticle moments that were blocked and the lower temperature peak to a transition to a collective super-spin glass type freezing state. The magnetic measurements showed that by increasing the size of the primary nanoparticles inside the clusters, the magnetic properties were enhanced which led to improvement of heating performance of clusters with bigger nanoparticles. ☐ In another project, hybrid nanoparticle clusters consisting of two chemically different nanoparticles (gold and iron oxide) were synthesized. It was observed that by increasing the gold concentration, the gold nanoparticle distribution starts to be more and more in the center of the clusters due to the lower surface energy of gold nanoparticles. Magnetic measurements showed that by increasing the gold concentration the blocking temperature was shifted toward lower temperatures which was due to the larger inter-particle spacing that leads to weaker inter-particle interactions. The magnetic hyperthermia measurements showed that the Specific Absorption Rate (SAR) value depends on the concentration of gold nanoparticles and it was higher for samples with more gold and this was due to the high heat capacity of the gold nanoparticles which shields the generated heat within the clusters. ☐ Finally, the impact of particle shape on the effective anisotropy and heating efficiency of magnetite nanoparticles was studied. Iron oxide nanoparticles were synthesized with three different shapes: spheres, cubes and octopods. The room temperature magnetic measurements indicated that maximum magnetization (at 30 kOe) of octopods was higher than cubes and spheres. It is believed that this is due to a limited distribution of disordered surface spins only on the corner of cubes and octopods as compared to a broader distribution of disordered spins at the surface of the spheres. The effective magnetic anisotropy constants for different shapes of nanoparticles were estimated using the law of approach to saturation and it was shown that the anisotropy of octopods was higher than that of cubes and spheres, which was also consistent with larger coercivity observed in the octopod particles. The hyperthermia measurements were studied on these three samples and it was observed that the increase of the effective anisotropy leads to an enhancement in the heating efficiency suggesting that the octopod particles are better agents for such magnetic treatments.
Description
Keywords
Heating efficiency, Iron oxide, Magnetic, Magnetic hyperthermia, Magnetism, Nanoparticle