Chromatographic methods for the separation and analysis of gold nanocrystals

With the ever growing applications of nanomaterials, fast, accurate and cost effective characterization methodologies are needed to ensure high quality materials and practical manufacturing. This problem is a challenging one as nanoparticle shape, size and size distribution are all important features which govern properties as diverse as sample melting point and chemical reactivity. New methods that provide key analytical information, along with a means of improving size and shape distributions would have substantial impact on this growing area. Chromatography is a technique which traditionally has been used to both provide analysis as well as separation of high valued added chemicals. Its applications in nanoscience are to date quite limited, and the objective of this thesis is to demonstrate that chromatographic techniques can be used to measure the dimensions of gold nanocrystals in solution as well as provide methods for physically separating complex distributions of particles. Recycling size exclusion chromatography (RSEC) has been employed to effect physical, base-line separation of subpopulations of spherical gold nanocrystals. This method can be easily applied on other nanocrystalline systems and is scalable to large production. Anisotropic gold nanocrystals, such as gold nanorods, exhibit spectacular optical properties that can be utilized in medical and biological fields. An analytical method, based on aqueous SEC that determines the dimensions of gold nanorods has been developed. The method couples the hydrodynamic volume obtained from SEC and aspect ratio from absorption spectra to provide a complete assessment of nanorod ensembles directly in liquid phase media. Additionally, a close analysis of the hydrodynamic values reveals that the nanorods are aligned with the flow, which makes the separation responsive to variations in aspect ratio. Finally, conventional chromatography provides a resolution which is not large enough to sharpen the distributions of the most monodisperse nanoparticles now produced directly in solution. The application of super high-resolution methods, such as critical point chromatography, can substantially improve the separation power and its application to polymer stabilized gold nanocrystals has been demonstrated