Publikationen

Nanoparticles may be taken up into cells via endocytotic processes whereby the foreign particles are encapsulated in vesicles formed by lipid bilayers. After uptake into these endocytic vesicles, intracellular targeting processes and vesicle fusion might cause transfer of the vesicle cargo into other vesicle types, e.g., early or late endosomes, lysosomes, or others. In addition, nanoparticles might be taken up as single particles or larger agglomerates and the agglomeration state of the particles might change during vesicle processing. In this study, liposomes are regarded as simple models for intracellular vesicles. We compared the energetic balance between two liposomes encapsulating each a single silica nanoparticle and a large liposome containing two silica nanoparticles. Analytical expressions were derived that show how the energy of the system depends on the particle size and the distance between the particles. We found that the electrostatic contributions to the total energy of the system are negligibly small. In contrast, the van der Waals term strongly favors arrangements where the liposome snugly fits around the nanoparticle(s). Thus the two separated small liposomes have a more favorable energy than a larger liposome encapsulating two nanoparticles.

This paper proposes an advanced image enhancement method that is specifically tailored towards 3-D confocal and STED microscopy imagery. Our approach unifies image denoising, deblurring and interpolation in one joint method to handle the typical weaknesses of these advanced microscopy techniques: out-of-focus blur, Poisson noise and low axial resolution. In detail, we propose the combination of (i) Richardson–Lucy deconvolution, (ii) image restoration and (iii) anisotropic inpainting in one single scheme. To this end, we develop a novel PDE-based model that realizes these three ideas. First we consider a basic variational image restoration functional that is turned into a joint interpolation scheme by extending the regularization domain. Next, we integrate the variational representation of Richardson–Lucy deconvolution into our model, and illustrate its relation to Poisson distributed noise. In the following step, we supplement the components of our model with sub-quadratic penalization strategies that increase the robustness of the overall method. Finally, we consider the associated minimality conditions, where we exchange the occurring scalar-valued diffusivity function by a so-called diffusion tensor. This leads to an anisotropic regularization that is aligned with structures in the evolving image. As a further contribution of this paper, we propose a more efficient and faster semi-implicit iteration scheme that also increases the stability. Our experiments on real data sets demonstrate that this joint model achieves a superior reconstruction quality of the recorded cell.

Composite bearings are normally produced with a layer of sintered bronze between the polymer coating and the metallic substrate, but omitting the extra bronze layer would reduce cost and manufacturing complexity. In this work, thermal impact welded metal-polymer composite specimen without sintered bronze layer are shaped to U-half shells to test them in a tribological test set up that is similar to the situation in a bearing. Wear rates and friction coefficient are measured for different pressure and velocity combinations. The effects of the shaping and their influence on wear behavior are examined by surface analysis, e.g., with SEM. Beside those shaping effects the heat balance is a very important influencing parameter on friction and wear behavior.

In this paper, we report the synthesis of one-dimensional zinc oxide (ZnO) nanostructures and the impact of their morphology on oxygen gas sensing properties. The nanostructures were synthesised via chemical vapour deposition using direct oxidation in an electrical furnace. Structural characterisation of the samples was performed with a field emission scanning electron microscope (SEM) and X-ray diffraction (XRD) methods. The SEM images revealed the formation of different sized nanowires, nanorods and nanoflower structures, and the XRD pattern showed hexagonal structures, without any impurities. The gas sensing properties of samples grown on silicon and alumina substrates were measured in different conditions. The samples grown on the alumina substrate showed better gas sensing properties than those grown on the silicon. To determine the optimal sensitivity, the oxygen gas sensing properties of the ZnO nanostructures were measured at different temperatures and gas flows. These nanostructural gas sensors showed high sensitivity at temperatures close to ambient. The effect of the morphology of ZnO nanostructures on their oxygen sensing properties was compared. Between the different synthesised nanostructures, ZnO nanowires exhibited the highest gas sensitivity.

In this paper, we studied the effects of the aluminium dopant concentration on the optical and electrical properties of aluminium doped zinc oxide (AZO) thin films grown on soda-glass substrates by a simple chemical method. The amount of aluminium in the compound was varied from 0 to 5 atomic percent (at.%), and the typical thickness of the films produced was about 300 nm. The thin films were characterized by scanning electron microscopy and X-ray diffraction to investigate the morphology and crystallinity of the samples. The optical properties of the thin films were studied by UV-Vis spectroscopy to determinate absorption, transmittance, and the diffuse reflectance. In addition, the photoluminescence properties of the thin films, excited with a 320 nm UV laser beam, were investigated. The effects of the aluminium concentration on these optical properties are discussed. The films with 2 and 5 % doping had excellent optical transmittance (~85-90 %) in the 400-1100 nm wavelength range. The photoluminescence spectra of the AZO films revealed UV near band edge emission peaks in the 378-401 nm range and an oxygen-vacancy related peak around 471 nm. The addition of aluminium changed the band gap of zinc oxide from 3.29 to 3.41 eV, and the appearance of a new level was observed in the band gap at the higher aluminium doping concentrations. The AZO thin films showed good conductivity (in the order of 10-2 Ω cm) which allows their use as transparent electrodes. Moreover, the AZO thin films were stable in open air for 30 days.

The stability of nanoparticle suspensions and the details of their agglomeration depend on the interactions between particles. We study this relationship in gold nanoparticles stabilized with different alkyl thiols in heptane. Temperature-dependent interactions were inferred from small-angle x-ray scattering, agglomeration kinetics from dynamic light scattering, and agglomerate morphologies from transmission electron microscopy. We find that the particles precipitate at temperatures below the melting temperatures of the dry ligands. Agglomerates grow with rates that depend on the temperature: Around precipitation temperature, globular agglomerates form slowly, while at lower temperatures, fibrilar agglomerates form rapidly. All agglomerates contain random dense packings rather than crystalline superlattices. We conclude that ligand-ligand and ligand-solvent interactions of the individual particles dominate suspension stability and agglomeration kinetics. The microscopic packing is dominated by interactions between the ligands of different nanoparticles.

We describe the self-assembly of silver nanocubes (AgNC) into dense bowl-shaped arrays using a template made from polystyrene nanospheres (PSNS). Interestingly, we found that most AgNCs were arranged facet-to-facet. When used as substrates for surface-enhanced Raman scattering (SERS), we observed that the SERS hot spot positions were located at the corners of the cubes. This was confirmed using the formation of a self-assembled monolayer (SAM) of 1-dodecanethiol (DDT) covering the cubes' facet surface, whilst the pinholes in the DDT SAM at the corners were subsequently filled with 2-mercaptopyridine (MPy). Due to the high enhancement from the densely arranged AgNCs, single molecule detection was achieved from this SERS substrate and evidenced using the bi-analyte Raman technique.

This Feature Article discusses two biomimetic aspects of functional particle surface assembly: the fabrication of biologically inspired structures from particles and the arrangement of particles on biomimetic templates. The first part discusses the creation of primary patterns by convective assembly and adsorption of particles that can be modified by a combination of etching and growth steps. Resulting structures mimic moth eyes, Lotus leaves, and the Gecko's adhesive structures, for example. The second part focusses on template assisted self-assembly (TASA) of particles. Herein, biological examples are inspiring in terms of structure formation related processes, rather than in terms of functionality. Template formation is a major bottleneck TASA. It is illustrated how bio-inspired wrinkling processes help overcoming this problem and can be employed for forming highly ordered functional nanoparticle assemblies.