Date of Award

12-2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Chemistry

Advisor

Chumanov, George

Committee Member

Marcus , Kenneth

Committee Member

McNeill , Jason

Committee Member

Luzinov , Igor

Abstract

Noble metal nanoparticles (NPs) have been used for many centuries; however their properties were not truly scrutinized until Michael Farady's investigations in the 1850's. Advances in the field of nanotechnology over the last three decades have enabled insights into the properties of materials as their dimensions are reduced to the nanoscale. The repercussions of these insights are seen in many modern applications.
In this dissertation, properties of novel nanostructures based on Ag NPs are presented and discussed. The exceptional optical properties of Ag NPs stem from the collective oscillations of the conduction electrons known as plasmon resonances. The excitation of plasmon resonances leads to the strongest known interaction of light with matter as compared to any known organic or inorganic chromophore.
A novel type of nanostructure, composed of Ag NPs capped with various materials and termed asymmetric hybrid nanoparticles (AHNs) was proposed and implemented. The concept of AHNs allows the addition of new properties to nanoparticles. Metals and dielectric materials were used as caps, imparting strong effects on the plasmon resonances of the AHNs. Multilayer AHNs were fabricated to render magnetic properties to Ag NPs.
The AHN concept led to the development of a novel type of optical labels. The labels are based on the surface enhanced Raman scattering (SERS) phenomenon from organic molecules sandwiched between Ag core and Ag cap. The observed strong SERS is well suited for multiplexed assays with optical detection. The structures were also used for fundamental SERS investigations. An alternative enhancement mechanism termed plasmon-induced electronic coupling was proposed from the results.
Capitalizing on their large cross-section for the interaction with light, Ag NPs were also investigated as optical labels based on light scattering. Ag NPs were encapsulated in silica shells, modified with amine functionalities, followed by conjugation with neutravidin molecules. Neutravidin offers a scaffold for attaching biotinylated biomolecules including antibodies. Silica shells provided nearly complete protection of Ag core in saline solutions often used in bioanalytical applications. The ongoing work focused on the application of these labels to flow cytometry.

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