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- ItemFusion of MALDI Spectrometric Imaging and Raman Spectroscopic Data for the Analysis of Biological Samples(Lausanne : Frontiers Media, 2018) Ryabchykov, Oleg; Popp, Jürgen; Bocklitz, Thomas W.Despite of a large number of imaging techniques for the characterization of biological samples, no universal one has been reported yet. In this work, a data fusion approach was investigated for combining Raman spectroscopic data with matrix-assisted laser desorption/ionization (MALDI) mass spectrometric data. It betters the image analysis of biological samples because Raman and MALDI information can be complementary to each other. While MALDI spectrometry yields detailed information regarding the lipid content, Raman spectroscopy provides valuable information about the overall chemical composition of the sample. The combination of Raman spectroscopic and MALDI spectrometric imaging data helps distinguishing different regions within the sample with a higher precision than would be possible by using either technique. We demonstrate that a data weighting step within the data fusion is necessary to reveal additional spectral features. The selected weighting approach was evaluated by examining the proportions of variance within the data explained by the first principal components of a principal component analysis (PCA) and visualizing the PCA results for each data type and combined data. In summary, the presented data fusion approach provides a concrete guideline on how to combine Raman spectroscopic and MALDI spectrometric imaging data for biological analysis.
- ItemTiO2 as Photosensitizer and Photoinitiator for Synthesis of Photoactive TiO2-PEGDA Hydrogel Without Organic Photoinitiator(Lausanne : Frontiers Media, 2018-8-7) Glass, Sarah; Trinklein, Betsy; Abel, Bernd; Schulze, AgnesThe replacement of potentially toxic photoinitiators is of increasing interest regarding the synthesis of biomaterials by photopolymerization. Therefore, we present a new method for the preparation of UV polymerized hydrogels with TiO2 as a photoinitiator. Titania is known to be an excellent photoactive compound which is non-toxic, inert, and cheap. The so-formed hydrogels possess excellent mechanical properties, a high swelling ratio, and high thermal stability. Furthermore, no TiO2 is released from the hydrogels. Thus, the material is highly suitable for medical applications. Additionally, the present TiO2 in the hydrogels remains photoactive as demonstrated by degradation of methylene blue. This enables the application of TiO2-hydrogels in photodynamic therapy.
- ItemScanning X-ray nanodiffraction from ferroelectric domains in strained K0.75Na0.25NbO3 epitaxial films grown on (110) TbScO3(Copenhagen : Munksgaard, 2017) Schmidbauer, Martin; Hanke, Michael; Kwasniewski, Albert; Braun, Dorothee; von Helden, Leonard; Feldt, Christoph; Leake, Steven John; Schwarzkopf, JuttaScanning X-ray nanodiffraction on a highly periodic ferroelectric domain pattern of a strained K0.75Na0.25NbO3 epitaxial layer has been performed by using a focused X-ray beam of about 100 14;nm probe size. A 90°-rotated domain variant which is aligned along [1 2]TSO has been found in addition to the predominant domain variant where the domains are aligned along the [12]TSO direction of the underlying (110) TbScO3 (TSO) orthorhombic substrate. Owing to the larger elastic strain energy density, the 90°-rotated domains appear with significantly reduced probability. Furthermore, the 90°-rotated variant shows a larger vertical lattice spacing than the 0°-rotated domain variant. Calculations based on linear elasticity theory substantiate that this difference is caused by the elastic anisotropy of the K0.75Na0.25NbO3 epitaxial layer.
- ItemFabrication of metal nanoparticle arrays by controlled decomposition of polymer particles(Bristol : IOP Publishing, 2013) Brodoceanu, Daniel; Fang, Cheng; Voelcker, Nicolas Hans; Bauer, Christina T.; Wonn, Anne; Kroner, Elmar; Arzt, Eduard; Kraus, TobiasWe report a novel fabrication method for ordered arrays of metal nanoparticles that exploits the uniform arrangement of polymer beads deposited as close-packed monolayers. In contrast to colloidal lithography that applies particles as masks, we used thermal decomposition of the metal-covered particles to precisely define metal structures. Large arrays of noble metal (Au, Ag, Pt) nanoparticles were produced in a three-step process on silicon, fused silica and sapphire substrates, demonstrating the generality of this approach. Polystyrene spheres with diameters ranging between 110 nm and 1 µm were convectively assembled into crystalline monolayers, coated with metal and annealed in a resistive furnace or using an ethanol flame. The thermal decomposition of the polymer microspheres converted the metal layer into particles arranged in hexagonal arrays that preserved the order of the original monolayer. Both the particle size and the interparticle distance were adjusted via the thickness of the metal coating and the sphere diameter, respectively.
- ItemHeteroepitaxial growth of T-Nb2O5 on SrTiO3(Basel : MDPI, 2018) Boschker, Jos E.; Markurt, Toni; Albrecht, Martin; Schwarzkopf, JuttaThere is a growing interest in exploiting the functional properties of niobium oxides in general and of the T-Nb2O5 polymorph in particular. Fundamental investigations of the properties of niobium oxides are, however, hindered by the availability of materials with sufficient structural perfection. It is expected that high-quality T-Nb2O5 can be made using heteroepitaxial growth. Here, we investigated the epitaxial growth of T-Nb2O5 on a prototype perovskite oxide, SrTiO3. Even though there exists a reasonable lattice mismatch in one crystallographic direction, these materials have a significant difference in crystal structure: SrTiO3 is cubic, whereas T-Nb2O5 is orthorhombic. It is found that this difference in symmetry results in the formation of domains that have the T-Nb2O5 c-axis aligned with the SrTiO3 <001>s in-plane directions. Hence, the number of domain orientations is four and two for the growth on (100)s- and (110)s-oriented substrates, respectively. Interestingly, the out-of-plane growth direction remains the same for both substrate orientations, suggesting a weak interfacial coupling between the two materials. Despite challenges associated with the heteroepitaxial growth of T-Nb2O5, the T-Nb2O5 films presented in this paper are a significant improvement in terms of structural quality compared to their polycrystalline counterparts.
- ItemElectronic structure and morphology of dark oxides on zinc generated by electrochemical treatment(London [u.a.] : Royal Society of Chemistry, 2013) Chen, Y.; Schneider, P.; Liu, B.-J.; Borodin, S.; Ren, B.; Erbe, A.Oxides formed by electrochemical treatment of metals frequently have properties and structures very different from the respective bulk oxides. Here, electronic structure and chemical composition were investigated for the oxide formed on polycrystalline zinc after electrochemical oxidation, and after subsequent reduction, in a Na2CO3 electrolyte. Photoluminescence and spectroscopic ellipsometry show the presence of states deep in the ZnO band gap in the oxidized sample, which consists of a highly disordered oxide. These states determine the absorption of light in the visible spectral range. After reduction, the characteristics of the ZnO electronic structure have disappeared, leaving a defect-dominated material with a band gap of ∼1.8 eV. Complementary detailed analysis of the morphology of the resulting surfaces shows hexagon-shaped metallic Zn-"nanoplates" to be formed in the reduction step. The optical appearance of the surfaces is dark, because of their efficient extinction of light over a large part of the visible spectrum. The optical appearance is a result of changed surface morphology and electronic structure of the oxide film. Such materials may possess interesting applications in photocatalysis or photoelectrochemistry.
- ItemAmorphous Li-Al-based compounds: A novel approach for designing high performance electrode materials for Li-ion batteries(Basel : MDPI AG, 2013) Thoss, F.; Giebeler, L.; Thomas, J.; Oswald, S.; Potzger, K.; Reuther, H.; Ehrenberg, H.; Eckert, J.A new amorphous compound with the initial atomic composition Al43Li43Y6Ni8 applied as electrode material for Li-ion batteries is investigated. Unlike other amorphous compounds so-far investigated as anode materials, it already contains Li as a base element in the uncycled state. The amorphous compound powder is prepared by high energy ball milling of a master alloy. It shows a strongly enhanced specific capacity in contrast to amorphous alloys without Li in the initial state. Therewith, by enabling a reversible (de)lithiation of metallic electrodes without the phase transition caused volume changes it offers the possibility of much increased specific capacities than conventional graphite anodes. According to the charge rate (C-rate), the specific capacity is reversible over 20 cycles at minimum in contrast to conventional crystalline intermetallic phases failing by volume changes. The delithiation process occurs quasi-continuously over a voltage range of nearly 4 V, while the lithiation is mainly observed between 0.1 V and 1.5 V. That way, the electrode is applicable for different potential needs. The electrode stays amorphous during cycling, thus avoiding volume changes. The cycling performance is further enhanced by a significant amount of Fe introduced as wear debris from the milling tools, which acts as a promoting element.
- ItemMicrofluidic-assisted silk nanoparticle tuning(Cambridge : Royal Society of Chemistry, 2019) Wongpinyochit, Thidarat; Totten, John D.; Johnston, Blair F.; Seib, F. PhilippSilk is now making inroads into advanced pharmaceutical and biomedical applications. Both bottom-up and top-down approaches can be applied to silk and the resulting aqueous silk solution can be processed into a range of material formats, including nanoparticles. Here, we demonstrate the potential of microfluidics for the continuous production of silk nanoparticles with tuned particle characteristics. Our microfluidic-based design ensured efficient mixing of different solvent phases at the nanoliter scale, in addition to controlling the solvent ratio and flow rates. The total flow rate and aqueous : solvent ratios were important parameters affecting yield (1 mL min−1 > 12 mL min−1). The ratios also affected size and stability; a solvent : aqueous total flow ratio of 5 : 1 efficiently generated spherical nanoparticles 110 and 215 nm in size that were stable in water and had a high beta-sheet content. These 110 and 215 nm silk nanoparticles were not cytotoxic (IC50 > 100 μg mL−1) but showed size-dependent cellular trafficking. Overall, microfluidic-assisted silk nanoparticle manufacture is a promising platform that allows control of the silk nanoparticle properties by manipulation of the processing variables.
- ItemSortase-Mediated Ligation of Purely Artificial Building Blocks(Basel : MDPI, 2018) Dai, Xiaolin; Mate, Diana M.; Glebe, Ulrich; Mirzaei Garakani, Tayebeh; Körner, Andrea; Schwaneberg, Ulrich; Böker, AlexanderSortase A (SrtA) from Staphylococcus aureus has been often used for ligating a protein with other natural or synthetic compounds in recent years. Here we show that SrtA-mediated ligation (SML) is universally applicable for the linkage of two purely artificial building blocks. Silica nanoparticles (NPs), poly(ethylene glycol) and poly(N-isopropyl acrylamide) are chosen as synthetic building blocks. As a proof of concept, NP–polymer, NP–NP, and polymer–polymer structures are formed by SrtA catalysis. Therefore, the building blocks are equipped with the recognition sequence needed for SrtA reaction—the conserved peptide LPETG—and a pentaglycine motif. The successful formation of the reaction products is shown by means of transmission electron microscopy (TEM), matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-ToF MS), and dynamic light scattering (DLS). The sortase catalyzed linkage of artificial building blocks sets the stage for the development of a new approach to link synthetic structures in cases where their synthesis by established chemical methods is complicated.