A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Functionalized Nanoparticles for the Controlled Modulation of Cellular Behavior(2023) Pendragon, Katherine Evelyn; Fisher, John; Delehanty, James; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to control cellular behavior at the single-cell level is of great importance for gaining a nuanced understanding of cellular machinery. This dissertation focuses on the development of novel hard nanoparticle (NP) bioconjugate materials, specifically gold nanoparticles (AuNPs) and quantum dots (QDs), for the controlled modulation of cellular behavior. These hard NPs offer advantages such as small size on the order of 1 – 100 nm, high stability, unique optical properties, and the ability to load cargo on a large surface area to volume ratio, making them ideal tools for understanding and controlling cell behavior. In Aim 1, we demonstrate the use of AuNPs to manipulate cellular biological functions, specifically the modulation of membrane potential. We present the conception of anisotropic-shaped AuNPs, known as gold nanoflowers (AuNFs), which exhibit broad absorption extending into the near-infrared region of the spectrum. We demonstrate the effectiveness of utilizing the plasmonic properties AuNFs for inducing plasma membrane depolarization in rat adrenal medulla pheochromocytoma (PC-12) neuron-like cells. Importantly, this is achieved with temporal control and without negatively impacting cellular viability. Aim 2 explores the use of QDs as an optical, trackable scaffold for the multivalent display of growth factors, specifically erythropoietin (EPO), for the enhanced induction of protein expression of aquaporin-4 (AQPN-4) within human astrocytes. This results in enhanced cellular water transport within human astrocytes, a critical function in the brain's glymphatic system. We show that EPO-QD-induced augmented AQPN-4 expression does not negatively impact astrocyte viability and augments the rate of water efflux from astrocytes by approximately two-fold compared to cells treated with monomeric EPO, demonstrating the potential of EPO-NP conjugates as research tools and prospective therapeutics for modulating glymphatic system function. Overall, the body of work presented in this dissertation develops new NP tools, namely solid anisotropic AuNFs and growth factor-delivering QDs, for the understanding and control of cell function. These new functional nanomaterials pave the way for the continued development of novel NP-based tools for the precise modulation of cellular physiology.Item Characterizing Atmospheric Turbulence with Conventional and Plenoptic approaches(2017) Ko, Jonathan; Davis, Christopher C; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Atmospheric turbulence is a phenomenon of interest in many scientific fields. The direct effects of atmospheric turbulence can be observed in everyday situations. The twinkling of stars is an indicator of weak atmospheric turbulence while the shimmering of objects above a hot surface is an indicator of strong atmospheric turbulence. The effects of atmospheric turbulence are generally considered a nuisance to optical applications. Image blurring effects are often present when observing distant objects through atmospheric turbulence. Applications that require maintaining the coherence of a laser beam, such as in free space optical communication, suffer from poor link quality in the presence of atmospheric turbulence. Attempts to compensate for the effects of atmospheric turbulence have varied in effectiveness. In astronomical applications, weak cases of atmospheric turbulence have been successfully compensated with the use of a Shack-Hartmann wavefront sensor combined with adaptive optics. Software techniques such as “Lucky Imaging” can be useful when clear images briefly appear through the presence of weak turbulence. However, stronger cases of atmospheric turbulence often found in horizontal or slant paths near the Earth’s surface present a much more challenging situation to counteract. This thesis focuses primarily on the effects of strong or “deep” atmospheric turbulence. The process of compensating for the effects of strong atmospheric turbulence begins with being able to characterize it effectively. A scintillometer measures the scintillation in the intensity of a light source to determine the strength of current turbulence conditions. Thermal fluctuation measurements can also be used to derive the strength of atmospheric turbulence. Experimental results are presented of a developed large aperture scintillometer, thermal probe atmospheric characterization device, and a transmissometer. While these tools are effective in characterizing atmospheric turbulence, they do not provide for a means to correct for turbulence effects. To compensate for the effects of atmospheric turbulence, the development of the Plenoptic Sensor is presented as a wavefront sensor capable of handling strong turbulence conditions. Theoretical and experimental results are presented to demonstrate the performance of the Plenoptic Sensor, specifically in how it leads to adaptive optics algorithms that can rapidly correct for the effects of turbulence.Item Controlling and Enhancing Atmospheric Optical/Plasma Filaments(2011) Varma, Sanjay Ramesh; Milchberg, Howard M; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As intense laser pulses propagate in atmosphere, they experience dramatic self-focusing, spectral broadening and phase modulation, and they ionize atmospheric molecules. The self-focusing and ionization-induced defocusing are competing effects that keep parts of the beam, called filaments, at high intensity over many Rayleigh lengths. Optical filaments and the plasma filaments that follow them are useful tools for remote sensing and ionization, atmospheric monitoring, terahertz generation, guiding of electrical discharges and optical pulse compression even to the few-cycle regime. Some of these applications may only be realized when the filamentation process is stabilized and plasma density is enhanced. Our experiments have shown that the rotational response of atmospheric nitrogen and oxygen is large enough and fast enough to dominate Kerr-induced self-focusing for optical pulses propagating with FWHM time duration > 40 fs. Moreover, our measurements have pointed to a way to greatly enhance the filament electron density by controlling the alignment of ambient N2 and O2 molecules and thereby controlling the optical nonlinearity or air. In addition, our group pointed out for the first time that quantum effects could dominate the propagation of intense femtosecond pulses in the atmosphere. This effect was demonstrated in our experiment that showed the quantum beats from laser-excited rotational wavepackets were able to steer, enhance or destroy laser filaments, depending on laser pulse timing. Our more recent work demonstrates that these quantum effects can increase the length of the plasma filament by a factor of three and can also promote soliton-like behavior of the pulse, cleaning and compressing it temporally. We performed direct measurements of the plasma density left behind by the filamenting optical pulses to confirm enhancement and extension of the electron density and laser intensity. Compression was measured with SPIDER, a technique for measuring the complex envelope and phase of optical pulses with sub-5 fs features.