Preparation, characterization, and stability of gold nanoparticles and gold nanoshells coated with mono-, bis-, and tris-chelating alkanethiols

Metal nanoparticles have been extensively studied because their optical properties and because they have great potential for emerging technological applications, such as corrosion prevention, chemical sensing, and microelectronic devices. The discovery of self-assembled monolayers (SAMs) has increased the usefulness of these metal nanoparticles. Self-assembled monolayers of thiolate compounds on the surfaces of metal nanoparticles, which are also known as monolayer-protected clusters (MPCS), have been used to stabilize metal nanoparticles.;This dissertation reports methods to functionalize gold nanoparticles (∼2 nm in diameter) with octadecanethiol (n -C18), 2-hexadecylpropane-1,3-dithiol (C18C2), 2-hexadecyl-2-methylpropane-1,3-dithiol( C18C3), and 1,1,1-tris(mercaptomethyl)heptadecane (t -C18). The latter three thiol compounds are designed to chelate with the metal surface, thus improving their stability. The resulting MPCs were characterized by ultraviolet-visible (UV-vis) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). After fully characterizing these composite nanoparticles, we evaluated their relative chemical stability by examining their resistance to etching by exposure to the cyanide ion.;Furthermore, the relative thermal stability of the targeted MPCs in solution was also investigated by using UV-vis spectroscopy. To study the effect of the substrate on the relative thermal stability of the designed adsorbates, self-assembled monolayers of the adsorbates were generated on both flat gold and gold nanoparticles. XPS was employed to verify the relative thermal stability of the SAMs generated on both surfaces.;Metal nanoshells have been pursued by industry because of their potential applications in conducting polymer devices, biosensing, drug delivery, cancer therapies, and laser-tissue welding. The study of the series of chelating alkanethiols was expanded to gold nanoshells with the ultimate goal of finding the best stabilizing agents for these typically larger metal nanoparticles. We functionalized gold nanoshells (∼150 nm in diameter), consisting of silica cores and ∼25 nm gold shells, separately with n -C18 and the chelating thiols: C18C2, C18C3, and t-C18. The resulting SAM-coated gold nanoshells were characterized by UV-vis, FT-IR, XPS, scanning electron microscopy (SEM), and TEM. After characterizing the properties of these composite nanoparticles, we evaluated their relative thermal stability by examining their optical properties in solution as a function of time.