Monolayer protected clusters: Fundamental properties and DNA binding

Chapter One is an introduction to fundamental properties of gold Monolayer-Protected Clusters (MPCs) including their synthesis, composition and structure, electrochemical and optical properties, and their assembly.; Chapter Two investigates binding of Au nanoparticles to DNA by ethidium intercalation. The ethidium sites are attached to the nanoparticles as thiolate ligands. The energy transfer quenching of the ethidium ligands by the metal-like MPC core is partially released by ethidium binding to DNA in solution. The increase in the intensity of ethidium fluorescence indicates the binding of MPCs to DNA. Different binding kinetics of the cationic TMA/ethidium MPC and negatively charged tiopronin/ethidium MPC to DNA are analyzed. The tiopronin/ethidium MPC binding to DNA is imaged by AFM.; Chapter Three presents the electrostatic assembly of cationic trimethyl(mercaptoundecyl)ammonium (TMA) MPCs along DNA molecules. One-dimensional chains of gold MPCs are prepared in solution by careful control of the relative molar quantities of nanoparticles and DNA base pairs. The gold core edge-edge distance in the TEM image is 2.9 +/- 0.9 nm, which is roughly twice the TMA monolayer thickness. Other and more complex patterns of DNA/MPC binding are observed in TEM images prepared from solutions by varying DNA/MPC mole ratios.; Chapter Four describes the separation of water-soluble tiopronin MPCs by electrophoresis. Interesting optical properties are observed from the separated MPCs. An inverse fourth power dependence of absorbance on the wavelength (lambda) is found from the smallest tiopronin MPCs obtained by electrophoresis. Near IR photoluminescence is detected and attributed to the surface related states. Quantum efficiencies from the separated MPCs and the luminescence mechanism are discussed.; Chapter Five focuses on the photoluminescence of the MPCs. The luminescence from various gold MPCs that have metal core size smaller than 2nm has been detected in the visible-near IR range. The emission is a broad band and ranges from approximately 650nm (1.9eV) to 1.3mum (0.9eV). The emission is believed to result from surface localized states, which not only depends on the size of the nanoparticles, but also the ligands attached on the metal surface and the charge states of the metal cores. Possible explanations and quantum efficiency are discussed.