Magnetic Nanocrystal Clusters: Understanding, Shaping, and Exploiting their Giant Susceptibility

Xiao, Zhen

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Year:: 2022
Contributor:: Xiao, Zhen (creator); Robinson, Jerome (Reader); Chen, Ou (Reader); Colvin, Vicki (Advisor); Brown University. Department of Chemistry (sponsor)
Genre:: theses
Subject:: Nanomaterial; Magnetic Nanoparticle; Cancer--Treatment; Magnetothermal heating; Magnetic particle imaging
Extent:: xxiii, 227 p.

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Abstract:: The ability to image, move, and heat magnetic nanomaterials at a distance has extraordinary promise for many biomedical and industrial applications. Realizing the promise, however, has been limited by the very large magnetic fields required to generate responses in nanoscale materials, particularly superparamagnets. Here we demonstrate how moderate exchange interactions between iron oxide nanocrystals interacting in clusters can lead to substantial enhancement of their initial magnetic susceptibility. The extraordinary sensitivity of these systems to magnetic fields enables portable magnetic heating and rapid stem cell capture using toy magnetic letters. The particles can also be applied in-vivo to eradicate solid tumors as well as improve the spatial resolution of magnetic particle imaging. We can amplify the sensitivity of magnetic nanocrystal clusters through doping with manganese; these systems are used for the first time to decompose environmental contaminants in water through the magnetic activation of thermal oxidation processes. Finally, we show how to further boost the DC magnetic susceptibility of these clusters by assembly into one-dimensional chains of controlled length. These hierarchical magnetic assemblies, which we refer to as nanoworms, in solution are freely rotating superparamagnets able to affect rapid mixing as nanoscale stir bars. In the solid state, aligned chains of nanoclusters exhibit high coercivities (up to 100 Oe) along one axis, with soft magnetic behavior along the other. Chapter 1 reviews the current synthetic strategies for making magnetic nanocrystal clusters with a focus on the proposed formation mechanism and dimensional control. Chapter 2 presents our systematic synthesis of diameter-controlled iron oxide nanocrystal clusters. Chapter 3 examines the size-dependent magnetic properties of the clusters and report their magnetic susceptibilities are about an order of magnitude higher than isolated nanoparticles. We apply the clusters for various biomedical applications and find the extraordinary sensitivity translates into improved performances. Chapter 4 demonstrates a further improvement in nanocluster magnetic susceptibility through manganese doping of iron oxide clusters. Finally, chapter 5 illustrates how even higher magnetic susceptibilities can result from the hierarchical assembly of nanocrystal clusters.
Notes:: Thesis (Ph. D.)--Brown University, 2022

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Citation

Xiao, Zhen, "Magnetic Nanocrystal Clusters: Understanding, Shaping, and Exploiting their Giant Susceptibility" (2022). Chemistry Theses and Dissertations. Brown Digital Repository. Brown University Library. https://repository.library.brown.edu/studio/item/bdr:bgv9y9ss/

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Chemistry Theses and Dissertations

Theses and Dissertations for the Chemistry department.
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