UC Santa Cruz

Abstract

Staci A. Adams

Magnetic and Plasmonic Properties of Metal and Metal-Oxide Nanoparticles and Their Applications

Nanomaterials are designed and synthesized for a wide range of applications including clinical diagnostics, therapeutics, the targeting of bioterrorism agents, wastewater treatment, energy, environmental remediation and sensing. In order to enhance performance in these fields researchers often work with materials that are either magnetic, plasmonic or a combination of both. Nanomaterials can be customized through synthetic variation in size, shape, aspect ratio, the dielectric constant of the surrounding media, surface morphology and whether particles are aggregated. Chapter 1 serves as an introduction to hollow gold nanospheres (HGNs) including their unique plasmonic properties and how these properties can be refined and harnessed for emerging applications. HGNs have hollow solvent filled dielectric cores and polycrystalline gold shells that, due to the two surfaces or interfaces, can generate an enhanced electromagnetic (EM) field. They possess a unique combination of properties that include small size (20-125 nm), large surface to volume (S/V) ratios, spherical shape, narrow and tunable SPR (~520-1000 nm) and biocompatibility. Their surfaces can also be easily functionalized to target and deliver biomolecules and are resistant to photobleaching. Additionally, their scattering and absorption cross-sections can be tailored, making them excellent candidates for a variety of applications including surface enhanced Raman scattering (SERS), sensing, imaging, drug delivery, site specific silencing and photothermal therapies (PTTs). Chapter 2 describes the detailed synthetic mechanism for creating highly reproducible near infrared (NIR) absorbing HGNs with an emphasis on the cobalt seed particle growth step of the synthesis. Several studies describing HGNs and their applications are found in chapter 3. The first study investigates the interaction of HGNs with Cu2+, commonly found in vivo, and the role that these ions play in aggregation, since aggregation can strongly influence the optical and photothermal properties of HGNs. The second study utilizes HGNs to visualize the Primo Vascular System (PVS) in a rat model. The use of hollow gold−silica double-shell (HGSDS) and hollow gold-silica composite (HGSC) nanostructures as surface enhanced Raman scattering (SERS) substrates for the detection of glucose is detailed in the third study found in chapter 3. Chapter 4 describes the synthesis of large Fe3O4@SiO2 nanoparticles (~200 nm) functionalized with gold and poly(vinylpyrrolidone) synthesized for bio-separation and SERS sensing applications. These particles have a unique surface morphology comprised of roughened gold nodules. The surface coatings prevent oxidation and render the particles easy to functionalize in order to target a wide range of moieties. The gold coverage is not only uniform across the entire particle surface but also ultra-thin so as to maintain a high percentage of the cores magnetic saturation (~68%) when compared to bare magnetite. The gold nodules facilitate the generation of hot spots that enhance the EM associated with the particle surface and are useful in sensing applications like SERS spectroscopy whereas the strong magnetic core allows for rapid separation (~30 s) of target molecules from solution once they are bound to the particles. Finally, in Chapter 5 the effect of polymer and gold functionalization on the magnetic properties of Fe3O4 nanoparticles is examined by superconducting quantum interference device (SQUID) and electron paramagnetic resonance (EPR) along with thoughts on future experimentation that can help to create a more complete story with respect to this unique nanocomposite material.