Browsing by Subject "Cell"

Now showing 1 - 8 of 8
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    Cell Response to Silica Gels with Varying Mechanical Properties
    (2013-07) Lefebvre, Molly
    Sol-gel encapsulation has a variety of applications in biotechnology and medicine: creating biosensors, biocatalysts, and bioartificial organs. However, encapsulated cell viability is a major challenge. Consequently, interactions between cells and their 3D microenvironment were studied through rheological, metabolic activity, and extraction studies to aid in the development of new gel protocols. The cells were encapsulated in variations of three silica sol-gels with varying stiffness. It was hypothesized that the cell viability and the amount of extracted cells would depend on gel stiffness. For two gels, there was no apparent correlation between the gel stiffness and the cell viability and extracted cell quantity. These gels did strongly depend on the varying gel ingredient, polyethylene glycol. The third gel appeared to follow the hypothesized correlation, but it was not statistically significant. Finally, one gel had a significantly longer period of cell viability and higher quantity of extracted cells than the other gels.
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    Electron transport and recombination in nanowire dye-sensitized solar cells.
    (2010-02) Enache-Pommer, Emil
    The dye-sensitized solar cell (DSSC) is a promising low cost photovoltaic device. A typical DSSC consists of a porous film made out of TiO2 nanoparticles, a monolayer of dye adsorbed on the TiO2 surface and a liquid electrolyte. The electrolyte fills the pores of the nanoparticle film forming a semiconductor-dye-electrolyte interface with large surface area. During illumination of the cell, the dye molecules inject electrons into the TiO2 nanoparticles. The injected electrons diffuse through the nanoparticle network by hopping from particle to particle until they are collected at a transparent conductive oxide (TCO) anode. Meanwhile, the charged dye molecules are reduced through an electrochemical reaction with a reductant in the electrolyte. The oxidized ionic species diffuse to the counter electrode and are reduced by electrons that have been collected at the anode and have traveled through the load to complete the circuit. Currently, dye-sensitized solar cells have reached efficiencies above 11 %, but further improvement is limited by electrons recombining with the electrolyte during their transport through the semiconductor nanoparticle network. Nanowire DSSCs have been recently introduced and have the potential to overcome the limitations of nanoparticle DSSCs, since the electron percolation through the nanoparticle network is replaced by a direct electron pathway from the point of injection to the TCO. Understanding the electron transport and recombination mechanisms in nanowire DSSCs is one of the key steps to improving DSSC efficiency. Towards this end polycrystalline TiO2, single-crystalline TiO2 and single crystalline ZnO nanowire DSSCs were fabricated and analyzed using current-voltage characteristics, optical measurements, and transient perturbation techniques such as intensity modulated photocurrent spectroscopy, photocurrent decay and open-circuit photovoltage decay. For single-crystal ZnO nanowire DSSCs, the measured electron transport time constants are independent of light intensity but change with nanowire length, seeding method and annealing time. Even if the measured transients are limited by the RC time constant of the solar cell, using the measured time constants as an upper limit for the actual electron transport time leads to the conclusion that the electron transport rate in ZnO nanowires is at least two orders of magnitude faster than the recombination rate. This indicates that the charge collection efficiency in ZnO nanowire DSSCs is nearly 100 %. These results show that films can be made out of 100 μm long ZnO nanowires while maintaining efficient charge collection. For DSSCs based on polycrystalline anatase TiO2 nanowires, the electron transport times show a power-law dependence on illumination intensity similar to that reported for TiO2 nanoparticle DSSCs. The magnitude of the electron transport times is also comparable to that of nanoparticle DSSCs, indicating that electron trapping and detrapping determine transport times for polycrystalline TiO2 nanowire DSSCs. Surprisingly, even for single-crystal rutile TiO2 nanowire DSSCs, the electron transport rate is on the order of the electron transport rate in nanoparticle-based DSSCs and not as fast as would be expected. Electron transport is slow and light intensity dependent indicating that trapping and detrapping, most likely in surface traps, still play an important role in electron transport even in single-crystal rutile TiO2 nanowires.
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    A non-invasive characterization of a biological cell using impedance spectroscopy
    (2012-11) Kim, Nahyoung
    This dissertation studies the electric characterization of biological cells by proposing an analytical model describing the electrical properties of a cell. This model is mathematically derived from electromagnetic phenomena of polarizable substances in electric field. It can provide the insight how the properties of each area, such as cell membrane, cytoplasm, nuclear envelope, effect the overall properties. Since biological cells tend to have a spherical shape in a cell suspension, it is modeled as a sphere or ellipsoid, containing a cell membrane, a cytoplasm, a nuclear envelope, and a nucleoplasm. The analytical equation for explaining the effects of a cell in electric field and the response of a cell in electric field is mathematically derived. This model can be applied in several areas, such as electroporation, dielectrophoresis and impedance spectroscopy. Impedance spectroscopy has been widely used as a characterization method for electrochemical systems and starting to be used in the biomedical area as a characterization tool, since it can facilitate a non-invasive characterization, which is not possible in a traditional biochemical method. The characterization of a cell using impedance spectroscopy requires an electrical circuit model or mathematical model describing the whole system. The proposed model can suggest more detailed and realistic mathematical and circuit model for a biological cell. The mathematical model for the impedance of a cell suspension is obtained by solving Laplace’s equation and Maxwell-Wagner’s equation. From the mathematical impedance model, a new equivalent circuit model is proposed to represent a cell suspension. The electric properties of a cell are calculated using the complex nonlinear least square method, which minimizes the square error between the measured impedance and the theoretically predicted impedance. This model is applied to study the conductivities and permittivities of the nucleoplasm, the nuclear envelope, the cytoplasm and the cell membrane of human embryonic stem cells (HSF-6) and induced pluripotent stem cells. Additionally, this model can be used in manipulation techniques, such as electroporation, electrofusion and dielectrophoresis. The transmembrane potential, which is the key factor in electroporation and electrofusion, and the Clausius-Mossotti factor, which determines the magnitude and the direction of dielectrophoretic force, are evaluated in detail.
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    The thermodynamic basis for the binding of lipids to annexin a5
    (2009-12) Knutson, Kristofer James
    Protein-membrane interactions are a vital mechanism of propagating signals both across the membrane and between cells. To control the magnitude and specificity of this type of cell signaling at the membrane, clustering of similar lipids and proteins has been observed in the cell via the formation of lipid microdomains. To address the thermodynamic basis of lipid induced signal propagation, we investigated how lipid microdomains form in response to annexin a5 binding to model membranes using Isothermal Titration Calorimetry (ITC). Annexins are known to bind to negatively charged (e.g., phosphatidylserine [PS]) membranes in a Ca2+-dependent manner. Based on Differential Scanning Calorimetry (DSC) results, we suggest that annexin functions to order lipid acyl chains upon binding and that the ordering of phospholipids can lead to the formation of microdomains. Using ITC, we have analyzed the membrane binding affinity of annexin for both gel and fluid state mixtures. Binding analysis of these isotherms shows that annexin binds fluid state mixtures with a significantly lower Kd than gel state (acyl chain ordered) lipids, which would be consistent with the hypothesis that binding of annexin a5 orders the acyl chains of the phospholipids. In addition, because the binding is entropically dominated but exhibits greater affinity for fluid compared to gel state lipids, we suggest that annexin binding is driven by the release of water molecules and ions as fluid lipids have more waters of hydration. Interestingly, the enthalpy associated with the binding process for both gel and fluid state lipid mixtures is small, indicative of a weak enthalpic association and suggestive of entropically mediated binding. We also present the binding of Eu3+ by a lanthanide binding complex (Tetra(N-(tert-butyl)-acetamide)-1,13-diamino-3,6,9-trioxadecane).
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    Tyr Flight 24
    (2014-09-03) Taylor, Brian
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    Tyr Flight 25
    (2014-09-03) Taylor, Brian
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    Tyr Flight 26
    (2014-09-03) Taylor, Brian
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    UAV Laboratories AEM Systems Group Seminar 20140926
    (2014-09-19) Taylor, Brian