Electrophoretic separations of monolayer protected clusters

Abstract

The determination of electrophoretic properties and the size separation of monolayer protected clusters (MPCs) are presented in this thesis. MPCs are metallic nanoparticles encapsulated in a protecting thiolate monolayer. Synthetic strategies yield MPCs that are resistant to agglomeration and decomposition, but typically have a polydisperse range of core sizes (1-8 nm). Due to their size, MPCs bridge the gap between bulk and molecular characteristics of gold or rather, varying sizes of MPCs exhibit bulk characteristics (large MPCs) or become more molecular in nature (small MPCs). Since the properties of MPCs are highly size dependent, the ability to isolate particular sizes of monodisperse nanoparticles will allow their use in applications with specific and uniform physical and chemical properties. Towards this end, we report optical characterization of MPCs that have been separated into more monodisperse fractions via continuous free-flow electrophoresis. Isolated MPC fractions were characterized using UV-Vis spectroscopy, near-infrared fluorescence, and capillary electrophoresis.

Place-exchange reactions offer a simple approach to better understanding the role of ligand composition of the protecting organic monolayer on the electrophoretic properties of MPCs. Water-soluble MPCs were place-exchanged with various thiolates and their electrophoretic properties were investigated using capillary electrophoresis. Noticeable trends were observed in the electrophoretic mobility of MPCs such as a decrease in electrophoretic mobility of the MPCs as the amount of place-exchange was increased. Understanding the effect of ligand exchange on the behavior of MPCs in the presence of an electric field is an important step for a variety of applications, including electrophoretic size separations.