Optical Properties and Application of Metallic Nanoparticles and their Assembled Superstructures.

Abstract

This dissertation reports the development of novel targeted contrast agents based on gold nanorods (GNRs) and their application in imaging cancer cells, cardiovascular inflammatory diseases and drug delivery monitoring using photoacoustic imaging (PAI). The GNRs based contrast agents were imaged with high signal-to-noise ratio (~17) and excellent spatial resolution (~250 micron) with concentration down to 10pM in biological tissues. The inherent disadvantage of limited imaging depth (~5 mm from skin surface) in PAI due to strong attenuation of light in biological tissues restricts the monitoring of drug delivery in intra-articular connective tissues. A novel targeted optical and nuclear dual-modality contrast agent was successfully developed by radiolabeling GNRs with [125I] to monitor anti-rheumatic drug delivery. PAI and nuclear imaging in combination present the detailed distribution of GNRs conjugated anti-rheumatic agent in intra-articular connective tissues with concentration down to 10 pM and radioactive label of 5 microCi . Radiolabeled contrast agents were further conjugated with polyethylene glycol (PEG) to increase the in vivo circulation time and prevent rapid clearance through accumulation into liver. Addition of PEG molecules on the surface of contrast agent increased the in vivo circulation time from 4 minutes to over 4 hours allowing specific targeting by the contrast agent.

Apart from application as a contrast agent, gold nanorods due to their anisotropic shape also form interesting building blocks for 3D superstructures with wide range of optical properties for applications in plasmonics, metamaterials and sensors. Under controlled evaporation monodisperse GNRs were self-assembled into micron sized three dimensional supercrystals. The highly organized supercrystals of GNRs with plasmonic antennae enhancement of electrical field have made possible the first real-time detection of prions (concentration down to 10^-10 M in complex biological media such as serum using surface enhanced raman scattering. CdTe nanoparticle-GNRs superstructures were made through biotin-streptavidin specific binding and investigated as potential gain materials for overcoming metallic losses in metamaterials through exciton-plasmon coupling. An extremely simple technique was developed to transfer gold nanorods from aqueous to organic medium, which allowed orientational ordering (order parameter of S~0.9) of low aspect ratio rods in dispersion through application of high electric fields.