Attachment of Pathogenic Prion Protein to Model Oxide Surfaces

Prions are the infectious agents in the class of fatal neurodegenerative diseases known as transmissible spongiform encephalopathies, which affect humans, deer, sheep, and cattle. Prion diseases of deer and sheep can be transmitted via environmental routes, and soil is has been implicated in the transmission of these diseases. Interaction with soil particles is expected to govern the transport, bioavailability and persistence of prions in soil environments. A mechanistic understanding of prion interaction with soil components is critical for understanding the behavior of these proteins in the environment. Here, we report results of a study to investigate the interactions of prions with model oxide surfaces (Al₂O₃, SiO₂) using quartz crystal microbalance with dissipation monitoring and optical waveguide light mode spectroscopy. The efficiency of prion attachment to Al₂O₃ and SiO₂ depended strongly on pH and ionic strength in a manner consistent with electrostatic forces dominating interaction with these oxides. The presence of the N-terminal portion of the protein appeared to promote attachment to Al₂O₃ under globally electrostatically repulsive conditions. We evaluated the utility of recombinant prion protein as a surrogate for prions in attachment experiments and found that its behavior differed markedly from that of the infectious agent. Our findings suggest that prions would tend to associate with positively charged mineral surfaces in soils (e.g., iron and aluminum oxides)

Photoluminescence and free carrier interactions in erbium-doped GaAs

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Incorporation of optically active erbium into GaAs using the novel precursor tris(3,5-di-tert-butylpyrazolato)bis(4-tert-butylpyridine)erbium

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Long wavelength emission of InGaAsNGaAsSb type II "w" quantum wells

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Characteristics of GaAsNGaAsSb type-II quantum wells grown by metalorganic vapor phase epitaxy on GaAs substrates

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Atomic Layer Deposited MgO: A Lower Overpotential Coating for Li[Ni_0.5Mn_0.3Co_0.2]O₂ Cathode

An ultrathin MgO coating was synthesized via atomic layer deposition (ALD) to improve the surface properties of the Li­[Ni_0.5Mn_0.3Co_0.2]­O₂ (NMC) cathode. An in-situ quartz crystal sensor was used to monitor the “self-limiting” surface reactions during ALD process and estimate the density of the deposited film. The electrochemical performance of the MgO-coated NMC cathode was evaluated in a half-cell assembly and compared to other ALD-based coatings, such as Al₂O₃ and ZrO₂. Cyclic voltammetry studies suggested that ALD MgO has a higher Li-diffusion coefficient which resulted in lower overpotential on the NMC cathode surface and improved Li-ion battery rate performance. MgO-coated NMC also yielded improved capacity retention over uncoated NMC in a long-range cycling test

Progress towards intersubband quantum-box lasers for highly efficient continuous wave operation in the mid-infrared

Intersubband Quantum-Box (IQB) lasers; that is, devices consisting of 2-D arrays of ministacks (i.e., 2-4 stages) intersubband QB emitters are proposed, as an alternative to 30-stage quantum-cascade (QC) devices, as sources for efficient room-temperature (RT) emission in the mid-infrared (4-6 µm) wavelength range. Preliminary results include: 1) the design of devices for operation with 50% wallplug efficiency at RT; 2) realization of a novel type of QC device: the deep-well (DW) QC laser, that has demonstrated at lambda =4.7µm low temperature sensitivity of the threshold current, a clear indication of suppressed carrier leakage; 3) the formation of 2-D arrays at nanopoles by employing nanopatterning and dry etching; 4) the formation of 40nm-diameter, one-stage IQB structures on 100nm centers by preferential regrowth via metal-organic vapor phase epitaxy (MOVPE).Defence Advanced Research Projects Agency (agreement number FA8650-07-1-7709

Resonantly Enhanced Nonlinear Optical Probes of Oxidized Multiwalled Carbon Nanotubes at Supported Lipid Bilayers

With production of carbon nanotubes surpassing billions of tons per annum, concern about their potential interactions with biological systems is growing. Herein, we utilize second harmonic generation spectroscopy, sum frequency generation spectroscopy, and quartz crystal microbalance with dissipation monitoring to probe the interactions between oxidized multiwalled carbon nanotubes (O-MWCNTs) and supported lipid bilayers composed of phospholipids with phosphatidylcholine head groups as the dominant component. We quantify O-MWCNT attachment to supported lipid bilayers under biogeochemically relevant conditions and discern that the interactions occur without disrupting the structural integrity of the lipid bilayers for the systems probed. The extent of O-MWCNT sorption was far below a monolayer even at 100 mM NaCl and was independent of the chemical composition of the supported lipid bilayer