Date of Degree

2-2014

Document Type

Dissertation

Degree Name

Ph.D.

Program

Chemistry

Advisor(s)

Hiroshi Matsui

Subject Categories

Mechanics of Materials | Nanoscience and Nanotechnology

Keywords

energy transfer, enzyme, lithography, microcontact printing, self-assembly, solar cell

Abstract

Recently, there has been a heightened amount of work done in the field of biomineralization. By taking inspiration from natures' phenomenonal individualities as a means to develop new and interesting nanostructures of varying sizes and dimensions, there is a newly developed design, namely Biomimetic Crystallization Nanolithography (BCN). With this method, the simultaneous nano-patterning and crystallization has been achieved using urease as the nucleation point and the hydrolysis of urea to obtain patterns of oxide semiconductor material, namely zinc oxide, at room temperature and aqueous solvent. The new and interesting characteristic of BCN involves the construction of amorphous inks of ZnO through the use of an enzyme, its hydrolyzing abilities, and Zn-precursors. These inks are nano-patterned with the tip of an atomic force microscope, which has found to induce the crystallization of the amorphous inks into crystalline patterns.

Also, a micro-contact printing process was developed and utilized as a means to directly pattern enzymes in a single step without the loss of enzyme activity after printing. By modifying the substrate to display aldehyde groups, the direct stamping of urease enables the simultaneous patterning and covalent cross-linking of urease under the reducing agent NaCNBH4, which does not degrade the enzyme activity. The exposed urease particles on the substrate, free from the cross-linker, were still catalytically active and utilized to grow crystalline ZnO nanoparticles on the enzyme patterns in ambient conditions and in aqueous solution.

Recently, there has been a growing demand to have the ability of fabricating nanosized structures that are 3D in orientation, produced in large quantities and yield uniform shapes and sizes. Biomimetic assembly has been given attention in that it relies on the use of bio-inspired materials that are characteristically organized from the macroscale all the way to the nanoscale. Peptides are one of nature's building blocks that have the ability to take an active role in self-assembly and that can further be integrated to consequently yield the self-organization of structures with interesting properties in high quantities. In this study, first, micron-sized assembly of streptavidin-functionalized Au nanoparticles and biotinylated collagen peptides into cubic structures was demonstrated as assembled peptide frameworks incorporate nanoparticles in the exact position of unit cell, and then other fluorescent molecules or nanoparticles with biotin moieties were co-assembled to generate complex 3D nanoparticle assemblies. Energy transfer (FRET) and excitonic lifetime change of between QDs (donors) and AuNPs (acceptors) in these assemblies were investigated. As the interparticle distance was changed, the FRET efficiency also changed, shown by emission lifetime measurements. The energy transfer efficiency was also affected by the number of acceptor nanoparticles around the donor QDs. This type of robust large-scale 3D material assembly technique with precise positioning could be beneficial for future bottom-up device assembly such as solar cells, batteries, and metamaterials.

 
 

To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.