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- ItemMicro-/nanostructured alumina as model surface to study topography effects on cell-surface interactions(SaarbrĂ¼cke : Leibniz-Institut fĂ¼r Neue Materialien, 2011) Aktas, Cenk; Martinez MirĂ³, Martina; Lee, Juseok; BrĂ¼ck, Stefan; Veith, Michael[no abstract available]
- ItemInfluence of carbon substrate on the electrochemical performance of carbon/manganese oxide hybrids in aqueous and organic electrolytes(Cambridge : Royal Society of Chemistry, 2016) Zeiger, Marco; Fleischmann, Simon; KrĂ¼ner, Benjamin; Tolosa, Aura; Bechtel, Stephan; Baltes, Mathias; Schreiber, Anna; Moroni, Riko; Vierrath, Severin; Thiele, Simon; Presser, VolkerManganese oxide presents very promising electrochemical properties as an electrode material in supercapacitors, but there remain important open questions to guide further development of the complex manganese oxide/carbon/electrolyte system. Our work addresses specifically the influence of carbon ordering and the difference between outer and inner porosity of carbon particles for the application in aqueous 1 M Na2SO4 and 1 M LiClO4 in acetonitrile. Birnessite-type manganese oxide was hydrothermally hybridized on two kinds of carbon onions with only outer surface area and different electrical conductivity, and conventional activated carbon with a high inner porosity. Carbon onions with a high degree of carbon ordering, high conductivity, and high outer surface area were identified as the most promising material, yielding 179 F g−1. Pore blocking in activated carbon yields unfavorable electrochemical performances. The highest specific energy of 16.4 W h kg−1 was measured for a symmetric full-cell arrangement of manganese oxide coated high temperature carbon onions in the organic electrolyte. High stability during 10 000 cycles was achieved for asymmetric full-cells, which proved as a facile way to enhance the electrochemical performance stability.
- ItemA novel precursor system and its application to produce tin doped indium oxide(Cambridge : Royal Society of Chemistry, 2011) Veith, Michael; Bubel, Carsten; Zimmer, MichaelA new type of precursor has been developed by molecular design and synthesised to produce tin doped indium oxide (ITO). The precursor consists of a newly developed bimetallic indium tin alkoxide, Me2In(OtBu)3Sn (Me = CH3, OtBu = OC(CH3)3), which is in equilibrium with an excess of Me2In(OtBu). This quasi single-source precursor is applied in a sol–gel process to produce powders and coatings of ITO using a one-step heat treatment process under an inert atmosphere. The main advantage of this system is the simple heat treatment that leads to the disproportionation of the bivalent Sn(II) precursor into Sn(IV) and metallic tin, resulting in an overall reduced state of the metal in the final tin doped indium oxide (ITO) material, hence avoiding the usually necessary reduction step. Solid state 119Sn-NMR measurements of powder samples confirm the appearance of Sn(II) in an amorphous gel state and of metallic tin after annealing under nitrogen. The corresponding preparation of ITO coatings by spin coating on glass leads to transparent conductive layers with a high transmittance of visible light and a low electrical resistivity without the necessity of a reduction step.
- ItemCarbon onion / sulfur hybrid cathodes via inverse vulcanization for lithium sulfur batteries(Cambridge : Royal Society of Chemistry, 2017) Choudhury, Soumyadip; Srimuk, Pattarachai; Raju, Kumar; Tolosa, Aura; Fleischmann, Simon; Zeiger, Marco; Ozoemena, Kenneth I.; Borchardt, Lars; Presser, VolkerA sulfur–1,3-diisopropenylbenzene copolymer was synthesized by ring-opening radical polymerization and hybridized with carbon onions at different loading levels. The carbon onion mixing was assisted by shear in a two-roll mill to capitalize on the softened state of the copolymer. The sulfur copolymer and the hybrids were thoroughly characterized in structure and chemical composition, and finally tested by electrochemical benchmarking. An enhancement of specific capacity was observed over 140 cycles at higher content of carbon onions in the hybrid electrodes. The copolymer hybrids demonstrate a maximum initial specific capacity of 1150 mA h gsulfur−1 (850 mA h gelectrode−1) and a low decay of capacity to reach 790 mA h gsulfur−1 (585 mA h gelectrode−1) after 140 charge/discharge cycles. All carbon onion/sulfur copolymer hybrid electrodes yielded high chemical stability, stable electrochemical performance superior to conventional melt-infiltrated reference samples having similar sulfur and carbon onion content. The amount of carbon onions embedded in the sulfur copolymer has a strong influence on the specific capacity, as they effectively stabilize the sulfur copolymer and sterically hinder the recombination of sulfur species to the S8 configuration.
- ItemCell adhesion on RGD-displaying knottins with varying numbers of tryptophan amino acids to tune the affinity for assembly on cucurbit[8]uril surfaces(Washington D.C. : American Chemical Society, 2017) Sankaran, Shrikrishnan; Cavatorta, Emanuela; Huskens, Jurriaan; Jonkheijm, PascalCell adhesion is studied on multivalent knottins, displaying RGD ligands with a high affinity for integrin receptors, that are assembled on CB[8]-methylviologen-modified surfaces. The multivalency in the knottins stems from the number of tryptophan amino acid moieties, between 0 and 4, that can form a heteroternary complex with cucurbit[8]-uril (CB[8]) and surface-tethered methylviologen (MV2+). The binding affinity of the knottins with CB[8] and MV2+ surfaces was evaluated using surface plasmon resonance spectroscopy. Specific binding occurred, and the affinity increased with the valency of tryptophans on the knottin. Additionally, increased multilayer formation was observed, attributed to homoternary complex formation between tryptophan residues of different knottins and CB[8]. Thus, we were able to control the surface coverage of the knottins by valency and concentration. Cell experiments with mouse myoblast (C2C12) cells on the self-assembled knottin surfaces showed specific integrin recognition by the RGD-displaying knottins. Moreover, cells were observed to elongate more on the supramolecular knottin surfaces with a higher valency, and in addition, more pronounced focal adhesion formation was observed on the higher-valency knottin surfaces. We attribute this effect to the enhanced coverage and the enhanced affinity of the knottins in their interaction with the CB[8] surface. Collectively, these results are promising for the development of biomaterials including knottins via CB[8] ternary complexes for tunable interactions with cells.
- ItemKelvin probe force microscopy of charged indentation-induced dislocation structures in KBr(SaarbrĂ¼cken : Leibniz-Institut fĂ¼r neue Materialien, 2009) Egberts, Philip; Bennewitz, RolandThe incipient stages of plasticity in KBr single crystals have been examined in ultrahigh vacuum by means of Atomic Force Microscopy and Kelvin Probe Force Microscopy (KPFM). Conducting diamond-coated tips have been used to both indent the crystals and image the resulting plastic deformation. KPFM reveals that edge dislocations intersecting the surface carry a negative charge similar to kinks in surface steps, while screw dislocations show no contrast. Weak topographic features extending in <110> direction from the indentation are identified by atomic-resolution imaging to be pairs of edge dislocations of opposite sign, separated by a distance similar to the indenter radius. They indicate the glide of two parallel {110} planes perpendicular to the surface, a process that allows for a slice of KBr to be pushed away from the indentation site.
- ItemCohesive detachment of an elastic pillar from a dissimilar substrate(Amsterdam : Elsevier, 2017) Fleck, Norman A.; Khaderi, Syed Nizamuddin; McMeeking, Robert M.; Arzt, EduardThe adhesion of micron-scale surfaces due to intermolecular interactions is a subject of in- tense interest spanning electronics, biomechanics and the application of soft materials to engineering devices. The degree of adhesion is sensitive to the diameter of micro-pillars in addition to the degree of elastic mismatch between pillar and substrate. Adhesion- strength-controlled detachment of an elastic circular cylinder from a dissimilar substrate is predicted using a Dugdale-type of analysis, with a cohesive zone of uniform tensile strength emanating from the interface corner. Detachment initiates when the opening of the cohesive zone attains a critical value, giving way to crack formation. When the cohe- sive zone size at crack initiation is small compared to the pillar diameter, the initiation of detachment can be expressed in terms of a critical value H c of the corner stress inten- sity. The estimated pull-offforce is somewhat sensitive to the choice of stick/slip boundary condition used on the cohesive zone, especially when the substrate material is much stiffer than the pillar material. The analysis can be used to predict the sensitivity of detachment force to the size of pillar and to the degree of elastic mismatch between pillar and sub- strate.
- ItemEpidermal growth factor receptor subunit locations determined in hydrated cells with environmental scanning electron microscopy(London : Nature Publishing Group, 2013) Peckys, Diana B; Baudoin, Jean-Pierre; Eder, Magdalena; Werner, Ulf; de Jonge, NielsImaging single epidermal growth factor receptors (EGFR) in intact cells is presently limited by the available microscopy methods. Environmental scanning electron microscopy (ESEM) of whole cells in hydrated state in combination with specific labeling with gold nanoparticles was used to localize activated EGFRs in the plasma membranes of COS7 and A549 cells. The use of a scanning transmission electron microscopy (STEM) detector yielded a spatial resolution of 3 nm, sufficient to identify the locations of individual EGFR dimer subunits. The sizes and distribution of dimers and higher order clusters of EGFRs were determined. The distance between labels bound to dimers amounted to 19 nm, consistent with a molecular model. A fraction of the EGFRs was found in higher order clusters with sizes ranging from 32–56 nm. ESEM can be used for quantitative whole cell screening studies of membrane receptors, and for the study of nanoparticle-cell interactions in general.
- ItemSurface-assisted laser desorption/ionization mass spectrometry using ordered silicon nanopillar arrays(Cambridge : Royal Society of Chemistry, 2014) Alhmoud, Hashim Z.; Guinan, Taryn M.; Elnathan, Roey; Kobus, Hilton; Voelcker, Nicolas H.Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) is ideally suited for the high-throughput analysis of small molecules in bodily fluids (e.g. saliva, urine, and blood plasma). A key application for this technique is the testing of drug consumption in the context of workplace, roadside, athlete sports and anti-addictive drug compliance. Here, we show that vertically-aligned ordered silicon nanopillar (SiNP) arrays fabricated using nanosphere lithography followed by metal-assisted chemical etching (MACE) are suitable substrates for the SALDI-MS detection of methadone and small peptides. Porosity, length and diameter are fabrication parameters that we have explored here in order to optimize analytical performance. We demonstrate the quantitative analysis of methadone in MilliQ water down to 32 ng mL-1. Finally, the capability of SiNP arrays to facilitate the detection of methadone in clinical samples is also demonstrated.
- ItemDatasets from a vapor diffusion mineral precipitation protocol for Dictyostelium stalks(Amsterdam : Elsevier, 2016) Eder, Magdalena; Muth, Christina; Weiss, Ingrid M.Datasets from a slow carbonate vapor diffusion and mineral precipitation protocol for Dictyostelium ECM and cellulose stalks show examples for composite materials obtained by an in vitro approach, which differs substantially from the in vivo approach reported in The Journal of Structural Biology, doi: 10.1016/j.jsb.2016.03.015 [1]. Methods for obtaining the datasets include bright field transmitted light microscopy, fluorescence microscopy, LC-PolScope birefringence microscopy, variable pressure scanning electron microscopy (VP-SEM/ESEM), and Raman imaging spectroscopy.