Deposition/Microfabrication Publications

2009

Bose S, MF Hochella, YA Gorby, DW Kennedy, DE Mccready, AS Madden, and BH Lower. 2009. "Bioreduction of hematite nanoparticles by the dissimilatory iron reducing bacterium Shewanella oneidensis MR-1." Geochimica et Cosmochimica Acta 73(4):962-976. Abstract The surface area normalized reduction rates of hematite (α-Fe2O3) nanoparticles, ranging in size from 11 to 99 nm, by S. oneidensis MR-1 with lactate as the sole electron donor were measured. The reduction kinetics of metal-oxide nanoparticles were examined to determine how S. oneidensis utilizes these environmentally-relevant solid-phase electron acceptors. Nanoparticles involved in geochemical reactions show different properties relative to larger particles of the same phase, and their reactivity is predicted to change as a function of size. As evident from whole cell TEM mounts, the mode of nanoparticle adhesion to cells is different between the more aggregated, pseudo-hexagonal to irregular shaped 11, 12, and 99 nm nanoparticles and the less aggregated 30 and 43 nm rhombohedral particles. Due to the aggregation differences, the 11, 12 and 99 nm particles show less cell contact and coverage than the 30 and 43 nm particles, but the former still show significant rates of reduction. This leads to the provisional speculation that S. oneidensis MR-1 employs a pathway of indirect electron transfer in conjunction with the direct-contact pathway, and the relative importance of the bioreduction mechanism employed may depend upon aggregation level, shape of the particles, and/or crystal faces exposed. In accord with the proposed increase in electronic band-gap for hematite nanoparticles with reduction in size, the smallest particles (11 nm) exhibit a one order of magnitude decrease in reduction rate (surface area normalized) when compared with larger (99 nm) nanoparticles, and the 12 nm rate falls in between these two. This effect may also be due to the passivation of the mineral and cell surfaces by Fe(II), or decreasing solubility due to decrease in size.
Wang H, D Wingett, MH Engelhard, K Feris, KM Reddy, P Turner, J Layne, C Hanley, J Bell, D Tenne, CM Wang, and A Punnoose. 2009. "Fluorescent Dye Encapsulated ZnO Particles with Cell-specific Toxicity for Potential use in Biomedical Applications." Journal of Materials Science. Materials in Medicine 20(1):11-22. Abstract Fluorescein isothiocyanate (FITC)-encapsulated core-shell particles with a nanoscale ZnO finishing layer have been synthesized for the first time as multifunctional “smart” nanostructures for particle tracking and cell imaging using the visible fluorescence emission of the dye or UV fluorescence emission of ZnO, and anti-cancer/antibacterial treatments using the selective toxicity of the nanoscale ZnO outer surface. The chemical phase composition, morphology, size, and the layered core-shell architecture of the particles were characterized using detailed transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis-NIR spectrophotometry. Systematic XPS studies after removing nanometer thick layers confirmed the expected layered structure in the order ZnO-SiO2-APTMS-FITC proceeding from the surface to the core of the ~200 nm sized particles. Detailed investigation of the fluorescence properties of these hydrophilic particles in bio-compatible media using fluorescence spectroscopy, flow cytometry and fluorescence confocal microscopy demonstrated that the silica/ZnO outer layer offers considerable protection to the encapsulated dye molecules from photobleaching and quenching due to reactive species such as oxygen in the solvent. These particles showed promise toward cell imaging, for example when the bacterium Escherichia coli was used as a test system, the green fluorescence of the particles allowed confocal microscopy to image the cells. The FITC encapsulated ZnO (FITC-ZnO) particles demonstrated excellent selectivity in preferentially killing Jurkat cancer cells (18% cell viability) without any significant toxicity to normal primary immune cells (75% cell viability) at 60 g/mL concentrations and inhibited the growth of both gram-positive and gram negative bacteria at concentrations ≥ 250-500 g/mL (for Staphylococcus aureus and Escherichia coli, respectively). These results indicate that the novel FITC encapsulated multifunctional particles with nanoscale ZnO surface layer are smart nanostructures for particle tracking, cell imaging, antibacterial treatments and cancer therapy.
Bell RC, K Wu, MJ Iedema, GK Schenter, and JP Cowin. 2009. "The Oil-Water Interface: Mapping the Solvation Potential." Journal of the American Chemical Society 131(3):1037-1042. doi:10.1021/ja805962x Abstract Ions moving across the oil water interface are strongly impacted by the continuous changes in solvation. The solvation potential for Cs+ is directly measured as they approach the oil-water interface (“oil” = 3-methylpentane), from 0.4 to 4 nm away. The oil-water interfaces are created at 40K using molecular beam epitaxy and a softlanding ion beam, with pre-placed ions. The solvation potential slope was determined at each distance by balancing it against an increasing electrostatic potential made by increasing the number of imbedded ions at that distance, and monitoring the resulting ion motion. The potential approaches the Born model for greater than z>0.4nm, and shows the predicted reduction of the polarizability at z<0.4nm.
Barry RC, Y Lin, J Wang, G Liu, and C Timchalk. 2009. "Nanotechnology-Based Electrochemical Sensors for Biomonitoring Chemical Exposures ." Journal of Exposure Science and Environmental Epidemiology 19:1-18. doi:10.1038/jes.2008.71 Abstract This manuscript highlights research focused on the development of field-deployable analytical instruments based on EC detection. Background information and a general overview of EC detection methods and integrated use of nanomaterials in the development of these sensors are provided. New developments in EC sensors using various types of screen-printed electrodes, integrated nanomaterials, and immunoassays are discussed. Recent applications of EC sensors for assessing exposure to pesticides or detecting biomarkers of disease are highlighted to demonstrate the ability to monitor chemical metabolites, enzyme activity, or protein biomarkers of disease. In addition, future considerations and opportunities for advancing the use of EC platforms for dosimetric studies are covered.
Kim BC, D Lopez-Ferrer, S Lee, H Ahn, S Nair, SH Kim, BS Kim, K Petritis, DG Camp, II, JW Grate, RD Smith, Y Koo, MB Gu, and J Kim. 2009. "Highly Stable Trypsin-Aggregate Coatings on Polymer Nanofibers for Repeated Protein Digestion." Proteomics 9(7):1893-1900. Abstract A stable and robust trypsin-based biocatalytic system was developed and demonstrated for proteomic applications. The system utilizes polymer nanofibers coated with trypsin aggregates for immobilized protease digestions. After covalently attaching an initial layer of trypsin to the polymer nanofibers, highly concentrated trypsin molecules are crosslinked to the layered trypsin by way of a glutaraldehyde treatment. This new process produced a 300-fold increase in trypsin activity compared with a conventional method for covalent trypsin immobilization and proved to be robust in that it still maintained a high level of activity after a year of repeated recycling. This highly stable form of immobilized trypsin was also resistant to autolysis, enabling repeated digestions of bovine serum albumin over 40 days and successful peptide identification by LC-MS/MS. Finally, the immobilized trypsin was resistant to proteolysis when exposed to other enzymes (i.e. chymotrypsin), which makes it suitable for use in “real-world” proteomic applications. Overall, the biocatalytic nanofibers with enzyme aggregate coatings proved to be an effective approach for repeated and automated protein digestion in proteomic analyses.
Jiang W, and WJ Weber. 2009. "Anisotropy of disorder accumulation and recovery in 6H-SiC irradiated with Au2+ ions at 140 K." Journal of Nuclear Materials 389(2):332-335. doi:10.1016/j.jnucmat.2009.02.023 Abstract Single crystal <0001>-oriented 6H-SiC was irradiated with Au2+ ions to fluences of 0.032, 0.058 and 0.105 ions/nm2 at 140 K and was subsequently annealed at various temperatures up to 500 K. The relative disorder on both the Si and C sublattices has been determined simultaneously using in-situ D+ ion channeling along the <0001> and <2-201> axes. A higher level of disorder on both the Si and C sublattices is observed along the <2-201>. There is a preferential C disordering and more C interstitials are aligned with <0001>. Room-temperature recovery along <2-201> occurs, which is associated with the <0001>-aligned interstitials that annihilate due to close-pair recombination. Disorder recovery between 400 and 500 K is primarily attributed to annihilation of interstitials that are misaligned with <0001>. Effects of stacking order in SiC on disorder accumulation are insignificant; however, noticeable differences of low-temperature recovery in Au2+-irradiated 6H-SiC and 4H-SiC are observed.
Kwak JH, D Mei, CWW Yi, DH Kim, CHF Peden, L Allard, and J Szanyi. 2009. "Understanding the nature of surface nitrates in BaO/gamma-Al2O3 NOx storage materials: A combined experimental and theoretical study ." Journal of Catalysis 261(1):17-22. Abstract The special role of the interface between the active catalytic phase (metal or metal oxide) and the oxide support in determining the properties of practical catalysts has long been recognized; however, it is still very poorly understood in most systems
Kimball BE, R Mathur, A Dohnalkova, AJ Wall, RL Runkel, and SL Brantley. 2009. "Copper isotope fractionation in acid mine drainage." Geochimica et Cosmochimica Acta 73(5):1247-1263. Abstract We surveyed the Cu isotopic composition of primary minerals and stream water affected by acid mine drainage in a mineralized watershed located in southwestern Colorado, USA. The 65Cu values (based on 65Cu/63Cu) of local enargite (65Cu = -0.01 ± 0.10‰) and chalcopyrite (65Cu = 0.16 ± 0.10‰) are within the general range of previously reported values for terrestrial primary Cu sulfides (-1 < 65Cu < 1). These mineral samples show lower 65Cu values than stream waters (65Cu = 1.36 - 1.74 ± 0.10‰), with an average isotopic fractionation (quantified as ∆aq-mino = 65Cuaq – 65Cu mino, where Cuaq is leached Cu and Cu mino is the original mineral) of 1.60 ± 0.14‰ and 1.43 ± 0.14‰ for enargite and chalcopyrite, respectively. To interpret this field survey, we simulated enargite and chalcopyrite leaching in batch experiments and found that, as in the field, leached Cuaq is isotopically enriched relative to primary minerals when microorganisms are absent (average ∆aq-min = 0.94 ± 0.14‰ for enargite, 1.18 ± 0.14‰ for chalcopyrite). Leaching of minerals in the presence of A. ferrooxidans results in smaller average fractionation in the opposite direction for chalcopyrite (∆aq-min = -0.57 ± 0.14‰) and no apparent fractionation for enargite (∆aq-min = 0.10 ± 0.14‰). The isotope effect during release of Cu from leaching minerals is inferred to be the same under both abiotic and biotic conditions. However, preferential association of isotopically enriched Cuaq with A. ferrooxidans cells, observed under TEM to occur as both localized precipitates around cells and Cu inside cells, is inferred to cause isotopic depletion of Cuaq in biotic experiments relative to abiotic experiments. Our results show indications of isotopic signatures of both abiotic chalcopyrite and enargite dissolution. Such signatures will be useful for AMD remediation and ore prospecting purposes.
Johnson BR, BJ Riley, SK Sundaram, JV Crum, CH Henager, Jr, Y Zhang, V Shutthanandan, CE Seifert, RM Van Ginhoven, CE Chamberlin, A Rockett, D Hebert, and A Aquino. 2009. "Synthesis and Characterization of Bulk Vitreous Cadmium Germanium Arsenide." Journal of the American Ceramic Society 92(6):1236-1243. doi:10.1111/j.1551-2916.2009.03001.x Abstract Abstract Cadmium-germanium-diarsenide (“CGA”) glasses were synthesized in bulk form (~2.4 cm3) using the procedures adapted from the literature. Several issues involved in the fabrication and quenching of amorphous CdGexAs2 (x = 0.45, 0.65, 0.85, 1.00) are described. An innovative processing route is presented to enable quenching of vitreous, crack-free ingots with sizes up to 10 mm diameter, and 30 – 40 mm long. Specimens from selected ingots were characterized using thermal analysis, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, particle-induced X-ray emission, Rutherford backscattering, secondary ion mass spectrometry, X-ray diffraction, density, and optical spectroscopy. Variations in properties as a function of processing conditions and composition are described. Results show that the density of defect states in the middle of the band gap and near the band edges can be decreased three ways: through suitable control of the processing conditions, by doping the material with hydrogen, and by increasing the concentration of Ge in the glass.
Du Y, NA Deskins, Z Zhang, Z Dohnalek, M Dupuis, and I Lyubinetsky. 2009. "Imaging Consecutive Steps of O2 Reaction with Hydroxylated TiO₂(110): Identification of HO₂ and Terminal OH Intermediates." Journal of Physical Chemistry C 113(2):666-671. Abstract We report results of the combined experimental and theoretical investigation of the molecular oxygen reaction with a partially hydroxylated TiO₂(110) surface. The consecutive steps of both primary and secondary site-specific reactions have been tracked with high-resolution scanning tunneling microscopy (STM). For the first time, we have directly imaged stable, adsorbed hydroperoxyl (HO₂) species, which is believed to be a key intermediate in many heterogeneous photochemical processes but generally metastable and “elusive” until now. We also found terminal hydroxyl groups, another critical but never directly observed intermediates. A conclusive evidence that O₂ reacts spontaneously with a single bridging OH group as an initial reaction step is provided. The experimental results are supported by density functional theory (DFT) calculations that have determined species energies and configurations. Reported observations provide a basis for a consistent description of the elementary reaction steps and offer molecular-level insight into the underlying reaction mechanisms. In a broader perspective, the results are expected to have far reaching implications for various catalytic systems involving the interconversion of O₂ and H₂O.

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