Surface Modifications of Nanometer- and Micron- Sized Particles and Their Applications

In this thesis, a generic method was developed for surface modification of nanoparticles (NP) with silica shell using Stöber method. Nanoparticles synthesized from nonhydrolytic solvents such as various ethers were first surface activated with a silane-based poly(ethylene glycol) (PEG). Because of the amphiphilicity of PEG moiety, these nanoparticles could be easily transferred from hydrophobic to hydrophilic solutions including different biological buffers. After ligand exchange with this silane-based PEG, silica deposition could happen on the surface of these nanoparticles using ethanol and water as solvents, ammonium hydroxide as catalyst and tetraethyl orthosilicate (TEOS) as precursor. This method has been successfully used to nanoparticles such as iron oxide, silver and Pt@iron oxide which were synthesized with oleic acid and/or oleylamine as capping agents. Hollow MPEG-sil-SiO2 nanoparticles were made from NP@MPEG-sil-SiO2 core-shell nanostructures by removing the metal or metal oxide cores using acid. Both core-shell and hollow nanoparticles were used in the drug delivery study of penicillin in the inhibition of Streptococcus. mutans. The inhibition zones show that hollow nanoparticles have larger loading capacity than core-shell ones. A new method has been developed for the formation of Pt@Fe2O3 yolk-shell nanostructures from Pt@Fe core-shell nanoparticles. Under the electron beam of TEM the oxidation of iron shells occurred and resulted in the formation of hollow structures because of the Kirkandall effect. The oxidation provided enough energy for Pt cores to hop, split and move in convective motion. This study demonstrates an approach of using