Master of Science / Department of Chemical Engineering / James H. Edgar / As a chemist who values purity of product, I have decided to look into various methods of filtration to ensure purity of final product. One such method is magnetic filtration of metallic impurities. For certain applications, the presence of ferromagnetic iron can increase magnetic susceptibility of certain items and therefore it must be removed selectively. One possible method of filtration that will bind much more selectively than a generic magnet is the use of nanoparticles. The following report is the research into what would be the best method of magnetic filtration using nanoparticles in a liquid slurry.

Semiconductor nanocrystals, also known as quantum dots (QDs), are a relatively new class of materials with unique size-dependent optical properties that enable the use of these materials in a variety of applications, including fluorescent labels for biomolecules, illumination and display technologies and photovoltaics. When the size of the QD is smaller than the mean separation of an optically excited electron-hole pair, or exciton, size-dependent fluorescence is observed as their emission peak shifts to larger wavelengths with increasing size. Doping of QDs with transition metals enables the tuning of their optoelectronic properties, leading to emission wavelengths longer than their bulk emission. The doping of QDs has recently garnered significant attention because it allows for the ability to tune the QD emission without changing its size. Currently, the most common method for synthesizing QDs involves the injection of organometallic precursors into hot coordinating solvents. To obtain monodisperse nanocrystals with this technique, instantaneous injection of the reactants, uniform nucleation over the entire reactor volume and perfect mixing are required. These conditions are difficult to achieve in practice, and even more difficult in a scaled-up reactor system necessary for commercial applications. The use of microemulsions as templates can enable the synthesis of semiconductor nanocrystals of uniform size and shape, and allow for scalability. The template used in this work consists of para-xylene as the continuous phase, water as the dispersed phase, and a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO37-PPO56-PEO37) block copolymer as the surfactant, with the reactants dissolved in the aqueous dispersed phase. Microemulsions formed by this technique, exhibit very slow droplet to droplet coalescence kinetics and allow for the growth of particles with narrow size distribution. A microemulsion template was used to synthesize Mn-doped ZnSe QDs using zinc-acetate and manganese-acetate as reactants which are dissolved in the aqueous dispersed phase. The microemulsion was placed in a reactor and hydrogen selenide gas was bubbled through the solution. A single ZnSe QD formed in each droplet of the microemulsion via an irreversible reaction between the precursors and coalescence of the resulting nuclei. The size of the nanocrystals was controlled to be between 5 and 8 nm by adjusting the initial concentration of zinc-acetate in water. The quantum confinement threshold for ZnSe is 9 nm and the bulk emission of ZnSe is 460 nm. The as-grown particles initially exhibit a size-dependent emission peak, attributed only to ZnSe, with a wavelength less than 460 nm. An emission peak at 585 nm, attributed to Mn2+ ions, appears after a few days in storage and increases substantially with time, eventually reaching a plateau. This indicates that ZnSe QDs are formed first and Mn2+ ions slowly diffuse into their lattice. The synthesis method employed in this work allows for a detailed study of dopant incorporation into ZnSe nanocrystals as a function of time. The time evolution of the intensity and the ratio of the ZnSe and Mn2+ emission peaks were studied as a function of dopant salt concentration in the precursor solution. A model was developed to describe the Mn2+ incorporation into the ZnSe nanocrystal by assuming that the Mn2+ to ZnSe emission intensity ratio is proportional to the amount of Mn2+ incorporated in the ZnSe lattice. To enable the use of the doped QDs in applications, a procedure was developed for extraction of the QDs from the template, capping with hydrophilic ligands, and stabilization in an aqueous solution. Experiments were also performed to accelerate the Mn2+ incorporation in the ZnSe lattice. A ZnSe layer was grown over the initial QDs and was found to substantially increase the fluorescence emission intensity. Additionally the synthesis technique was expanded to use liquid crystals as templates with the purpose of growing Mn-doped ZnSe nanostructures, such as nanodiscs or nanowires, which have potential applications in nanoelectronics.

Modern semiconductor fabs are multi-billion dollar systems capable of producing devices with features as small as 7 nm for a cost of nano-dollars each. The nanoscale devices they fabricate have reshaped the world. Whole new fields of nanoscience have opened up encouraged by the success of the semiconductor industry and the promise of nanotechnology. Modern nanoscientists largely use tools pioneered in and for semiconductor fabs. Here, some of the functionality of semiconductor fabs is reproduced on millimeter size silicon chips, creating new tools for researching and manufacturing nanodevices. A system of these silicon chips is a fab-on-a-chip and is built using microelectromechanical systems or MEMS. MEMS devices are inexpensive to fabricate, but can be extremely complex. The first fab-on-a-chip device presented is a micro-scale thermal evaporator. It can deposit 7 Å s^-1 of Pb from ∼1 mm away, can be rapidly reloaded using simple mechanical means, and has a footprint of 0.25 mm^2. The flux rate from this thermal evaporator is monitored using a re-purposed quartz crystal oscillator as a mass sensor. Another fab-on-a-chip device is a writer. A device capable of positioning a silicon plate with <10 nm resolution in two dimensions. It can be used either to position stencils of nanoscale devices or to draw nanoscale devices directly in a process called atomic calligraphy. A micro-evaporator has been connected to a writer to form a device that is capable of producing nanoscale structures while only being a few cubic millimeters large. Additionally, an advanced writer is presented that can move a plate with five degrees of freedom and could be a powerful tool for fabricating and manipulating nanodevices.

Actin filament assembly and mechanics are crucial for muscle contraction, maintenance of cell structure, motility, and division. Actin filament assembly occurs in a crowded intracellular environment consisting of various types of molecules, including small organic molecules known as osmolytes. Ample evidence highlights the protective functions of osmolytes such as trimethylamine-N-oxide (TMAO), including their effects on protein stability and their ability to counteract cellular osmotic stress. Recently, TMAO has been shown to counteract the denaturing effects of urea on actin filament assembly based on bulk fluorescence assays. Yet, how TMAO affects individual actin filament assembly dynamics and mechanics is not well understood. We hypothesize that, owing to its protective nature, TMAO will enhance filament assembly kinetics and stiffen actin filaments due to increased stability. In this study, we investigate osmolyte-dependent actin filament assembly kinetics and bending mechanics by measuring filament elongation rates and bending persistence lengths in the presence of TMAO using total internal reflection fluorescence (TIRF) microscopy imaging and pyrene fluorescence assays. We demonstrate that TMAO enhances increases the elongation rates of individual filaments as well as steady-state average filament lengths and enhances filament bending stiffness. Taken together, our results show that the physiochemical properties of the intracellular environment can regulate actin assembly dynamics and mechanics. This study will help identify molecular mechanisms of how small organic osmolytes modulate cytoskeletal protein filament assembly and mechanics in living cells.

Gold Nanoparticles have piqued interest for use in a wide range of diagnostic and therapeutic applications including biosensors, assays, vaccine development, drug delivery, and photothermal therapy. While extensive research has been conducted, the applications of gold nanoparticles have yet to see the same level of commercial success as well-established methods such as ELISA and lateral flow immunoassays. Studies analyzing the efficacy of gold nanoparticle technologies in vivo and in vitro provide seemingly conflicting results that reflect a further need for investigation into the biological response of gold nanoparticles. A large factor in the variation is the nature of the interaction between gold nanoparticles and the immune system. The immune system is among the first systems involved with the initial interaction with a foreign entity, and is comprised of several mechanisms for a variety of circumstances. While current studies have begun to provide insight regarding immunological response to gold nanoparticles, further research is still required. In this study, the interactions between gold nanoparticles and 13 different immunoglobulin isotypes from bovine, human, and murine blood were studied using dynamic light scattering, colorimetry, and UV-Vis spectroscopy. In further testing, gold nanoparticle interaction was monitored in mixed samples of immunoglobulin isotypes associated with T helper 1 and T helper 2 cell pathways to potentially observe any change in interaction as the result of a mixed sample. Preliminary results revealed a potential trend involving a greater increase in absorbance and hydrodynamic radius for isotypes associated with the T helper 1 cell related immune response. However, certain inconsistent repeatability of the results was noticed from the mixed immunoglobulin studies, and this observation seems to indicate the possibility of additional factors contributing to the immunoglobulin-gold nanoparticle interactions.

Myelination and node of Ranvier formation play an important role in saltatory conduction of axonal action potentials in the peripheral nervous system (PNS). Degeneration or damage of this myelin can lead to impairment in the conduction of signals by the axons, and cause deficits in sensory and motor function. Currently, animal-based models are the primary method used to study myelination; however, data generated in animal models generally translate poorly to humans, especially as applied to drug discovery. In order to accurately study myelination in humans without having to rely on human testing, an engineered in vitro model of myelination could go a long way in helping us understand the mechanisms of myelination, as well as provide a platform to test drugs or therapeutics to treat diseases that affect myelination. Here we report the complete development and characterization of the first human myelination model using human primary Schwann cells (SCs) and human iPSC-derived motoneurons (iPSC-MNs) as well as some data collected from furthering this work utilizing iPSC derived Schwann cells. Myelination and node of Ranvier formation in co-cultured iPSC human motoneurons and primary human SCs were characterized via flow cytometry, immunocytochemistry, and 3D confocal Raman microscopy, and furthering of this work using iPSC derived human Schwann cells characterized using immunocytochemistry is also presented. This novel human-based myelination model will be a more accurate tool when it comes to the study of myelination and demyelinating diseases in humans, as well as elucidation of mechanisms of myelination. This system(s) could be used to determine efficacy of novel therapeutics for demyelinating diseases such as Charcot-Marie Tooth, Guillian-Barre syndrome, anti-MAG peripheral neuropathy, as well as the testing of treatments for the regeneration of damaged peripheral myelination from other causes.

Actin monomers and filaments are reorganized into bundled structures at the leading edge of cells by bacterial pathogens to aid pathogen entry into host cells. Chlamydia trachomatis infection utilizes the translocated actin-recruiting phosphoprotein (Tarp), a secretion effector protein that alters the actin cytoskeleton to assist in internalizing the bacterium. A previous study on Tarp-bundling mechanics demonstrates that Tarp can form bundles with higher flexibility than bundles induced by other actin bundling proteins such as fascin in vitro. Understanding the bending stiffness, length and assembly rate dynamics of Tarp-induced bundles in vitro is critical for understanding the invasion mechanism of C. trachomatis, therefore simulating a cellular environment by observing Tarp in the presence of molecular crowders is vital. Trimethylamine N-oxide (TMAO) is a natural organic osmolyte which regulates osmotic stress and stabilizes protein structure by favoring the folded conformational state. Due to its ability to stabilize proteins in aqueous conditions, we hypothesize that TMAO will aid Tarp in restructuring actin filaments by increasing the bundling efficiency of Tarp and forming bundles with physiologically relevant mechanical strength. In this study, we investigate how TMAO affects Tarp's bundling efficiency and the mechanical properties of Tarp induced actin bundles using total internal reflection fluorescence (TIRF) microscopy, polymerization kinetics, and biophysical analysis. We show that moderate concentrations of TMAO increase the bundling efficiency of Tarp while forming more rigid bundles compared to Tarp-bundles in dilute buffer conditions. This in vitro model allows for characterizing Tarp-induced bundles in the presence of TMAO, giving insight on how the Chlamydia trachomatis bacterium triggers cytoskeletal rearrangements, beginning a complex infectious process in living cells.

No description available.

The creation of molecular machines has been one of the goals of modern nanotechnology for a few decades. Such machines can be assembled from small molecules, as well as DNA. Of particular interest are mechanically interlocked nanoconstructs – catenanes and rotaxanes. These structures offer developments such as nanoswitches and rotational motors. DNA nanotechnology has produced numerous systems that consist of catenanes that could perform programmable switching and stimuli-responsive behaviour, as well as switching between stations in a semi-autonomous, rotary, motor-like behaviour. Energy transduction and the speed of such Brownian ratchet motors are negligible when compared to natural enzymatic activity. Bridging the gap between enzymology and structural DNA nanotechnology, we propose a method to assemble and operate a prototype system of fully complementary interlocked ssDNA rings that can roll against each other as a pair of gears with a ratio 1:2. The directionality and force is proposed to be generated by a strand-displacing polymerase enzyme performing a rolling circle amplification reaction on one of the members of this catenane, generating torque. Computer modelling of this system using oxDNA script package has been carried out, enabling both the topological visualisation and structural inquiry into the system prior to experimental development. Variations to the system such as changing the overall size, gearing ratio and developments towards integration into larger assemblies have also been described and are discussed in detail. Several experimental assembly strategies are described, together with experimental evidence of their outcomes. A method for operation of the single-stranded DNA catenane as a pair of continuously rolling gears has been investigated using strand displacing polymerases. Applications and suggestions for future developments is provided, addressing integration into complex systems. Additional methods of assembly and operation are discussed and compared.

<p>Be-doped InP nanowires were grown by the gold-assisted vapour-liquid-solid mechanism in a gas source molecular beam epitaxy system. The nanowires were characterized by scanning and transmission electron microscopy. With increased doping, the dependence of the length on diameter [L(D)] underwent an unusual transition from the diffusion-limited 1/D² relationship to one that increased before saturating. Doping influences on crystal structure and radial growth have been reported previously, but in the absence of these effects it is speculated that the beryllium introduces an increase in the steady-state chemical potential of the catalyst, and a barrier to nucleation. A model is presented relating the diffusion- and nucleation-limited regimes.</p> <p>Additionally, the progressive increase of dopant incorporation was verified by secondary ion mass spectrometry. Samples were transformed into a "bulk-like" material by spin-coating with cyclotene to enable depth profiling. Carrier concentrations were inferred through comparison with a thin film reference, and agreed in order of magnitude with the nominal doping values.</p> <p>Dopant activation was investigated through micro-photoluminescence experiments, and showed peak emissions between 1.49 eV and 1.50 eV for undoped samples, transitioning with increased doping to 1.45-1.46 eV. The difference between the dominant peak energies was consistent with differences reported for comparable epitaxially-grown thin film samples. Bandgap narrowing was also observed at high levels of doping, and was consistent with theoretical predictions.</p> <p>As a whole, the work presented here provides a different perspective on the effects of doping on nanowire growth, demonstrated through the specific system of Be-doped InP. The findings have implications for predictable and consistent nanowire device design, and suggestions for avenues of future research are provided.</p> / Master of Applied Science (MASc)