|dc.description.abstract||This dissertation focuses on four research topics: self-assembly of colloidal nanoparticles, surface modifications of the properties of ionically self-assembled multilayer films, surface enhanced Raman spectroscopy of functionalized gold nanoparticles, and two photon uncaging in gel. Those techniques are used for development of novel nanofabrication methods for top-down and bottom-up assembly of nanostructures, by modifying the properties of nanopatterned surfaces with photoactive ligands, and other technologies.
First I describe the development of an improved method for nanosphere lithography, a variation of the convective self-assembly technique. The method exhibited high reproducibility and yielded high quality monolayer crystals by withdrawing a meniscus of liquid polystyrene spheres solution and subsequent evaporation of the solvent. The monolayer crystal was used as an evaporation mask to create surface arrays of gold nanotriangular particles.
Metal nanoparticles, with sharp features or narrow gaps, exhibit strong plasmonic properties. I took advantage of those properties to attempt to create patchy modifications of the surface functionalization of gold nanotriangular particles treated with photosensitive molecules. Two molecules denoted, P3-DTC, and LIP3, were used as functional molecules attached to the gold nanoparticles. After interaction with 356nm UV light, part of those molecules cleaves off the surface of the nanoparticles rendering the surface modified with a new functional group. The modification takes place only at the plasmonic hot spots of those nanoparticles, resulting in a patchy modification of the properties of the nanoparticles.
I built polymer Ionically Self-assembled Multilayer (ISAM) films using a Layer-by-Layer deposition technique and treated them to alter their surface adhesion properties. Poly (allylamine hydrochloride) (PAH), and poly (styrene sulfonate) (PSS) are a very well-studied system of polyelectrolytes for LbL deposition. ISAM films built from those polyelectrolytes are rich in amine groups to which nanoparticles, cells, tissue cultures, ligands can be made to adhere. In my work I developed a method for selective modification of the surface adhesiveness, by neutralizing the amine groups trough acetylation with acetic anhydride. With resolution from a few microns to a few hundred nanometers, I selectively passivated some areas of the ISAM film while others I left unaltered. I tested the effect of the acetic anhydride passivation by performing Horse Radish Peroxidase (HRP) test which quantifies the amount of free amines on the surface of the film. I also demonstrated the patchy modification of surface adhesiveness by introducing gold nanospheres which attached only to the amine active areas of the modified ISAM film.
Photoactivatable fluorophores, i.e. compounds and other entities that may transform into a fluorescent form on absorption of a photon can be employed in multidimetional volume patterning. I studied the photoactivation of aryl azides in gelatin matrix. Specifically, I used Azidocoumarin 151 as a test molecule to undergo two-photon activation, and then measured the resulting photoluminescence. The activation of the Azidocoumarin 151 can be used to create arbitrary 3D patterns of modified functionality inside the gel. The activated molecules can be used as sites for further modification of the patterning inside the volume of the gel. Possible modifications include attaching biomolecules, nanoparticles, or individual cells.
I would like to acknowledge my adviser Hans Robinson for giving me the opportunity to work on several very interesting projects. Dr. Robinson has thought me critical thinking and supported greatly my research in his laboratory. He was always kind and willing to discuss scientific ideas and therefore contributed to my development as a successful graduate student.
Iâ d like to also thank Dr. Richie Davis and Dr. Webster Santons for the useful discussions about my projects. I had the great pleasure to work closely with several graduate students during my time at Virginia Tech. Kai Chen, helped me get into the field of polymer self assembled films. I worked closely with Jason Ridley on modifying surface properties of ISAM films. Brandon Thorpe has been a constant supplier of a variety of compounds that I used in my SERS studies. Iâ d like to thank my fellow graduate students from Dr. Robinsonâ s group, Chih-Yu Jao, Eric See, Kirby Mayers, for being great company and lending help when I need it.
During my stay at Virginia Tech I have met some wonderful faculty and staff at the Department of Physics. They were all very helpful, but Iâ d like to extend special thanks to Chris Thomas, Dr. Ghiti Khodaparast, Dr. Mark Pitt, Dr. Tetsuro Mizutani, and Randy Heflin.
Finally, Iâ d like to thank my wife Elitsa for being patient during my time as a graduate student. Iâ d like to also thank my daughter Eleonora and son Alexander for being the cutest kids in the world and for cheering me up all the time.||en_US
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