<p> As a class of carbon-based nanomaterials, single-walled carbon nanotubes (SWNT) have many structural variations, called chiralities, each with different properties. Many potential applications of SWNT require the properties of a single chirality, but current synthesis methods can only produce single chiralities at prohibitive costs, or mixtures of chiralities at more affordable prices. Post-synthesis chirality separations provide a solution to this problem, and hydrogel separations are one such method.</p><p> Despite much work in this field, the underlying interactions between SWNT and hydrogel are not fully understood. During separation, large quantities of SWNT are irretrievably lost due to irreversible adsorption to the hydrogel, posing a major problem to separation efficiency, while also offering an interesting scientific problem concerning the interaction of SWNT with hydrogels and surfactants. </p><p> This thesis explores the problem of irreversible adsorption, offering an explanation for the process from a mechanistic viewpoint, opening new ways for improvement in separation. In brief, this work concludes adsorption follows three pathways, two of which lead to irreversible adsorption, both mediated by the presence of surfactants and limited by characteristics of the hydrogel surface. These findings stand to increase the general understanding of hydrogel SWNT separations, leading to improvements in separation, and bringing the research field closer to the many potential applications of single-chirality SWNT.</p><p>

With the technological advances of today, comes the increasing need for device miniaturization. This thesis focuses on the construction of nanostructures, approached from both bottom-up (synthesis) and top-down (lithography) methods. First, a bottom-up method to construct cadmium selenide semiconductor nanoparticles under mild conditions in reverse micelles is described and investigated. A detailed spectroscopic study of nanoparticle growth is provided, whereby the growth was monitored over a period of up to a year. The nanoparticles were removed from the surfactant using ethanol precipitation and were subjected to surface derivatization in order to stabilize them. Secondly, photoreversible cycloaddition of an anthracene derivative is studied for use in double-exposure lithography. The system was found to be adequately reversible, though possible side photoreactions were investigated. Spectroscopic studies were also conducted and photophysical pathways of the compound were examined. The compound was found to have a cleaving quantum yield of 0.67 +/- 0.04 and was established as an actinometer to assess the efficacy of future candidate compounds.

Apoptosis (programmed cell-death) is a common final pathway through which cells die in retinal degenerative diseases. The purpose of this project was to develop biodegradable nanoparticles that quickly deliver XIAP, an inhibitor of apoptosis, to retinal cells following acute insults. In vitro protein release profiles from different formulations were established, and two cell types were incubated with nanoparticles to assess cellular uptake. Subretinal injections were carried out in rats to assess in vivo localization and possible toxicity. In vitro studies showed an initial burst of protein followed by sustained release, with overall low levels of protein release. Cell culture experiments suggest that particles are mostly membrane-bound, and some may be internalized. In vivo experiments revealed no signs of toxicity, and protein localized within the photoreceptor layer. In conclusion, nanoparticles may provide a good delivery system for XIAP; however higher levels of protein release are needed for neuroprotection, warranting further investigation.

Ferrihydrite is a natural iron hydroxide occurring mostly in surface waters. In the last 40 years, six different structures have been proposed for ferrihydrite, without reaching consensus in the scientific community. The contradictory debate around the nanostructure of ferrihydrite represents the principal motivation of the present thesis, i.e., to verify systematically all structure proposals instead of just the most accepted ones. We compare powder x-ray diffraction patterns recorded from synthetic samples of 2-lines and 6-lines ferrihydrite with the calculated ones (Debye sum) from the proposed structures. The comparisons show that all structure propositions are incorrect. Although, three of the six propositions suggest jointly that oxygen atoms form a double-hexagonal close packing structure in ferrihydrite and that the exact structure determination problem could be solved by finding the correct positions of the iron atoms inside the oxygen layers.

Porous metal oxide materials, particularly those comprised of silica or titania, find use in many applications such as low-k dielectric materials for microelectronics as well as chemical sensors, micro/nanofluidic devices, and catalyst substrates. For this dissertation, the focus will be on the processing of porous metal oxide materials covering two subjects: hierarchical porosity exhibited over two discrete length scales and incorporation of functional nanomaterials. To generate the porous silica materials, the technique of supercritical carbon dioxide infusion (scCO2) processing was heavily relied upon. Briefly, the scCO2 infusion processing utilizes phase selective chemistries within a pre-organized amphiphilic block copolymer template using scCO2 as the reaction medium to selectively hydrolyze and condense silica precursors to yield mesoporous materials. To further develop the scCO 2 infusion processing technique, hierarchically porous silica materials were generated on unique substrates. Hierarchically structured silica nanochannels were created using a combination of scCO2 infusion processing and nanoimprint lithography (NIL) patterned sacrificial polymer templates to yield mesopores and airgap structures respectively. Hierarchically porous silica materials were also generated on alternative substrates, in the form of cellulose filter paper, which were used to host the amphiphilic block copolymer template to yield tri-modal porosity silica materials. To extend the applicability of mesoporous silica generated from scCO 2 infusion processing, functional nanomaterials, in the form of pre-synthesized gold nanoparticles, fullerene derivatives, and polyhedral oligomeric silsequioxanes (POSS) were embedded within the mesoporous silica to produce unique composite materials. The functional nanomaterials were able to impart specific properties, typically only affored to the functional nanomaterials, upon the mesoporous silica thin film with an example being enhanced thermal and hydrothermal properties of mesoporous silica doped with POSS molecules. To continue research with functional nanomaterials, nanoparticle composite materials, comprised of crystalline metal oxide nanoparticles and binder/filler materials, either organic or inorganic, were also evaluated as novel NIL resist materials. Patterning of the nanoparticle composite materials, specifically, but not limited to, titanium dioxide based materials, into two dimensional, arbitrarily shaped, sub-micron features was readily achieved on either rigid or flexible substrates. True three-dimensional structures, based on nanoparticle composite materials, were fabricated by utilizing release layers and pre-patterned substrates.

Nanoparticles are regarded as exciting new building blocks for functional materials due to their fascinating physical properties because of the nano-confinement. Organizing nanoparticles into ordered hierarchical structures are highly desired for constructing novel optical and electrical artificial materials that are different from their isolated state or thermodynamics random ensembles. My research integrates the surface chemistry of nanoparticles, interfacial assembly and lithography techniques to construct nanoparticle based functional structures. We designed and synthesized tailor-made ligands for gold, semiconductor and magnetic nanoparticle, to modulate the assembly process and collective properties of the assembled structures, by controlling the key parameters such as particle-interface interaction, dielectric environments and inter-particle coupling etc. Top-down technologies such as micro contact printing, photolithography and nanoimprint lithography are used to guide the assembly into arbitrarily predesigned structures for potential device applications.

The colloidal behavior of engineered nanomaterials exposed in an aquatic environment may significantly influence their bioavailability as well as toxicity to different species. Natural organic matter (NOM) is one of the major colloidal materials ubiquitous in the environment with significant structural heterogeneity. Therefore, role of NOM molecules on environmental fate of these engineered NPs needs to be addressed. Colloidal behavior of aluminum (Al2O 3) and magnetic iron oxide (γFe2O3) NPs was studied in the presence of structurally different HAs and synthetic polyacrylic acids (PAAs). The conformation behavior of the adsorobed NOM/polyelectrolyte under specific solution conditions were determined with dynamic light scattering, atomic force microscopy measurements. Al2O3 NPs followed the classical DLVO model of colloidal behavior in their pristine state. However, a significant deviation from the classical DLVO model was observed when these NPs were coated with structurally different HAs. Low polar, high molecular weight HA fractions showed much stronger stabilization against Ca2+ induced aggregation. Previously, we observed that these low polar, high molecular weight fractions strongly destabilized the NP suspension when added in a small quantity. A significant transformation in suspension stability was observed possibly due to steric effect of these adsorbed HAs. The colloidal behavior of PAA/NOM coated ferrimagnetic γFe 2O3 NPs were investigated. Pure γFe2O 3 NPs were extremely unstable in aqueous solution but a significant enhancement in colloidal stability was observed after coating with polyelectrolytes/NOM. The steric as well as electrostatic stabilization introduced by the polyelectrolyte coating strongly dictated the colloidal stability. The alteration of electrosteric stabilization mechanisms by pH-induced conformation change profoundly influences the colloidal stability. Atomic force microscopy (AFM) study revealed a highly stretched conformation of the HA molecular chains adsorbed on γFe 2O3 NP surface with increasing pH from 5 to 9 which enhanced the colloidal stability trough long range electrosteric stabilization. The depletion of the polyelectrolytes during dilution of the suspension in the acidic solution conditions and in the presence of Na+ or Ca 2+ decreased the colloidal stability. The conformation of the polyelectrolytes adsorbed on the NP surface altered significantly as a function of substrate surface charge as viewed from the AFM imaging.

No description available.

Screening for effects of small molecules on cells grown in culture is a well-established method for drug discovery and testing, and faster throughput at lower cost is needed especially for lipophilic materials. Small-molecule arrays present a promising approach. However, it has been a challenge to use them to obtain quantitative surface based dose-response curves in vitro, especially for lipophilic compounds. This thesis first introduces a simple novel method of surface-mediated delivery of drugs to cells from a microarray of phospholipid multilayers (layers thicker than a bilayer) encapsulating small molecules. The capability of controlling the dosage of the lipophilic molecules delivered to cells using the lipid multilayer microarray assay is further demonstrated using the nanointaglio printing method. This control enabled the variation of the volumes of surface supported lipid micro- and nanostructure arrays fabricated with nanointaglio. The volumes of the lipophilic drug-containing nanostructures were determined using a fluorescence microscope calibrated by atomic-force microscopy. The surface supported lipid volume information was used to obtain EC-50 values for the response of HeLa cells to treatment with three FDA-approved lipophilic anticancer drugs, docetaxel, imiquimod and triethylenemelamine, which were found to be significantly different from neat lipid controls. Features with sub-cellular lateral dimensions were found to be necessary to obtain normal cell adhesion with HeLa cells. Comparison of the microarray data to dose-response curves for the same drugs delivered liposomally from solution revealed quantitative differences in the efficacy values, which may be explained in terms of cell-adhesion playing a more important role in the surface-based assay. Finally, solution encapsulation was done for a library of hydrophilic silicon nanocrystals in order to set a solution standard for comparison with future surface supported delivery of the library. The work presented here opens the door for the possible benchtop high throughput and high content screening of hydrophobic materials that were previously difficult or impossible to readily screen. / A Dissertation submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of in partial fulfillment of the Doctor of Philosophy. / Spring Semester 2016. / March 28, 2016. / Dose response, Drug screening, High throughput screening, Lipid multilayers, Microarray, Nanointaglio / Includes bibliographical references. / Steven Lenhert, Professor Directing Dissertation; Jingjiao Guan, University Representative; Thomas Keller, Committee Member; Bryant P. Chase, Committee Member; Teng Ma, Committee Member.

Nanoscience and nanotechnology research has provided us with new paradigms of technologies to improve human life, but still there is plenty of room to expand its frontiers. In order to do so, we need to pursue the development and study of novel nanostructures with the main goal of understanding the physical properties and finding potential applications. Understanding the physics of low-dimensional systems is the first step to fostering the corresponding technological applications. Considering this premise, the goal of this dissertation is to study two distinct classes of heterogeneous nanowires (NWs): phosphorous-doped Si NWs with an axial doping gradient and metal NWs grown on DNA templates. The Si NWs grown by vapor-liquid-solid chemical vapor deposition were utilized to fabricate Schottky barrier-limited field-effect transistors (FETs), which have shown significant promise in the areas of electronics and sensing because of their unique characteristics. The idea of utilizing the modulation of the nano Schottky junction at a metal-semiconductor interface promises higher performance for chemical and biomolecular sensor applications when compared to conventional FETs with Ohmic contacts (exponential versus linear responses). However, the fabrication of such asymmetric FETs presents challenges such as reproducibility through complications in the fabrication processes. We have been able to circumvent the fabrication difficulties and reproducibility problems by utilizing our Si nanowires synthesized by a chemical vapor deposition process which yields a pronounced doping gradient along the length of the NWs. This inhomogenous doping in NWs has typically been seen as a detrimental characteristic; however, we have taken advantage of this doping profile as the basis of our approach. The graded doping profile facilitates definition of a series of metal contacts on a single NW that systematically evolve from Ohmic to Schottky with increasing effective barrier height along the axial direction. The study of this systematic variation is presented in this dissertation as a proposal to obtain devices for sensing and electronic applications. The main results of our research is recently published. The fabrication and study of metal NWs is the second effort discussed in this dissertation. The main motivation is to address the fundamental question of whether a true superconducting state could exist in one dimension. The answer to this question lies in the nature of superconducting fluctuations of the order parameter that describe the coherent behavior of the Cooper pairs. In a superconducting system, the order parameter has a well-defined amplitude and phase. The superconducting fluctuations occur in the form of phase slips which can be either thermally activated or quantum mechanical. Although much experimental and theoretical work has been done on the topic, an unambiguous resolution of this issue remains elusive mainly due to the challenge of producing NWs having the dimensions of the cross-section of the NW smaller than the superconducting coherence length or the size of the Cooper pairs. Our approach to overcome the fabrication difficulties to reach the true 1D limit is a unique combination of DNA templates and low temperature quench-condensation for in situ fabrication and measurement of superconducting NWs with a width of just a few nanometers. In this dissertation, details on the fabrication and our initial results demonstrating the capability of our DNA molecular templates to reach small cross-section metal NWs are presented; also, we present systematic characterizations of the electrical properties of metal nanowires with respect to in situ variation of the geometry of the nanowire. This effort has laid a full foundation for a comprehensive examination of superconductivity in 1D reaching unprecedentedly small cross-sections. A manuscript summarizing these results is in preparation. / A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester 2017. / April 11, 2017. / DNA templates, metal nanowires, Schottky energy barrier, silicon nanowires / Includes bibliographical references. / Peng Xiong, Professor Directing Dissertation; Jingjiao Guan, University Representative; Nicholas E. Bonesteel, Committee Member; Irinel Chiorescu, Committee Member; Jorge Piekarewicz, Committee Member.