Fabrication of Hollow Magnetic Nanoparticles for Bio-medical Applications

Abstract

Hollow inorganic nanoparticles with nano-sized cavity space encapsulated in an inorganic nanoshell have been of great interest in terms of science application. In the past decade, research has shown that their unique properties are beneficial for a variety of applications, including nanoreactors, drug delivery vehicles, and contrast agents for medical imaging, and energy and gas storage materials. Two features of hollow nanoparticles - extremely high surface to volume ratio, and nanosize isolated cavity - could provide the novel functionality as nanocatalyst with specific reactions at the surface, or nanoreactors that contain catalytic species inside the cavity. For instance, the researchers change the structure of the paramagnetic nanoparticles to hollow structures to maximize the relaxation of the neighboring water protons on the surface of the nanoparticles or introduce functional yolk inside the hollow nanoparticles to induce specific reactions within only inside the cavity. As such, the hollow nanoparticles combine their structural properties with the intrinsic properties of the material, enabling a variety of tasks what would not possible with solid counterpart structures of identical material. In this thesis, I proposed new fabrication method for the novel hollow nanoparticle, made of magnetic material that can be used in the bio-imaging and intracellular catalysis application field. The magnetic properties of the hollow nanoparticle can establish themselves as a highly enhanced T1-weighted magnetic resonance imaging (MRI) contrast agents, or alternating magnetic field (AMF) stimuli activated catalyst, which I describe in chapter 2 and 3. First, I found that the relaxivity of hollow manganese oxide nanoparticles (HMON) depends on the magnetization value of particles under the magnetic field. In the process of producing highly water accessible and well colloidal HMON-based contrast agents, I found that the relaxivity of the HMON changed in the opposite direction as expected, and found that the reason was ligand capping altered the magnetic properties of the HMON to the particle surface, which affects relaxivity. This study is described in chapter 2 in more details. Secondly, I designed the fabrication method for the Fe3O4/Pd@h-SiO2 bioorthogonal catalytic nanoreactor activated by AMF induced localized heating. The AMF induced localized heating from the relaxation of the magnetic domain inside Fe3O4 yolk has a role for the kinetic control of Pd nanodot growth location only inside the cavity. The synthesized Fe3O4/Pd@h-SiO2 have a potential to catalyze the bioorthogonal reaction from activated Pd nanodot by AMF induced localized heating. The hollow nanostructure can provide the protected space from the complex bio-medium and maintain the bulk temperature from localized heating, which can affect cell viability. More detailed information and procedure are described in chapter 3. In conclusion, these suggested approaches would enable us to further expand the application field utilizing the structural characteristics of hollow nanostructures.