Publikationen

In this work, the field dependence of the magnetocaloric effect of Gd bulk samples has been enhanced through nanostructuring of the material. Nanostructuring consists in multilayers preparation by alternative rf-sputtering deposition of Gd layers and Ti spacers onto glass substrates. The results obtained for the multilayers were compared to those obtained for the Gd bulk. Assuming a power law for the field dependence of the magnetic entropy change (ΔSM ∝ Hn), higher field dependences close to the transition in a wider temperature range are obtained for the multilayer material (n = 1.0) with respect to the bulk counterpart (n = 0.78). The effect of a Curie temperature distribution in the multilayer material (due to variations of the layer thickness) has been studied through numerical simulations to explain the observed field dependence of the magnetocaloric effect, obtaining a remarkable agreement between experiments and results.

Coinage-metal nanoparticles are key components of many printable electronic inks. They can be combined with polymers to form conductive composites and have been used as the basis of molecular electronic devices. This review summarizes the multidimensional role of surface ligands that cover their metal cores. Ligands not only passivate crystal facets and determine growth rates and shapes; they also affect size and colloidal stability. Particle shapes can be tuned via the ligand choice while ligand length, size, ω-functionalities, and chemical nature influence shelf-life and stability of nanoparticles in dispersions. When particles are deposited, ligands affect the electrical properties of the resulting film, the morphology of particle films, and the nature of the interfaces. The effects of the ligands on sintering, cross-linking, and self-assembly of particles in electronic materials are discussed.

A semicontinuous process is used to nanoimprint a nanowire ink and form transparent conductive electrodes. Ultrathin gold nanowires are confined in the features of an elastomeric stamp, where they spontaneously assemble upon drying into hierarchical, percolating superstructures. This templated self-organization yields grids with defined line widths down to 0.9 µm and high pattern fidelity. Metal grids with square, hexagonal, and linear features are printed over 30 cm2 on different substrates and gently sintered in hydrogen plasma. Meshes on polyethylene terephthalate foil show high optical transmittances (>92%) and low sheet resistances (106–168 Ω sq−1). Their resistance is changed by only 10% after 500 bending cycles at a radius of 5 mm. The printed electrodes are used to build capacitive and resistive touch sensor devices.

Ionic liquids (ILs) exhibit tunable behaviour and properties that are due to their supramolecular structure. We synthesized a series of alkylated and fluorinated phosphonium dicyanamide ILs to study the relation between molecular structure and assembly with a focus on the roles of cation chain length and fluorination. Small angle X-ray scattering indicated a lamellar structure with long-range order for all fluorinated ILs, while alkylated ILs showed only the general structures of ILs, i.e., alternating a polar ionic-zone and a nonpolar alkyl-zone. "Fluorophobic" interactions caused microphase segregation between perfluorinated and other molecular segments, "fluorophilic" interactions among the perfluorinated segments stabilized the microphase structure, and the coupling of "fluorophobic" and "fluorophilic" interactions resulted in a stable mesophase structure. The perfluorinated segments packed more densely than the alkylated analogues; the fluorinated versions (except for F2) liquefied at temperatures considerably above that of alkylated ILs. The lamellar structures strongly affected the rheology of the ILs. Fluorinated ILs had higher viscosities and exhibited non-Newtonian shear thinning; the alkylated ILs of the same length had an order of magnitude lower viscosities and were purely Newtonian. We propose that the disruption of lamellar structure in the shear flow causes the non-Newtonian flow behaviour.

Hierarchical structures lend strength to natural fibers made of soft nanoscale building blocks. Intermolecular interactions connect the components at different levels of hierarchy, distribute stresses, and guarantee structural integrity under load. Here, we show that synthetic ultrathin gold nanowires with interacting ligand shells can be spun into biomimetic, free-standing microfibers. A solution spinning process first aligns the wires, then lets their ligand shells interact, and finally converts them into a hierarchical superstructure. The resulting fiber contained 80 vol % organic ligand but was strong enough to be removed from the solution, dried, and mechanically tested. Fiber strength depended on the wire monomer alignment. Shear in the extrusion nozzle was systematically changed to obtain process–structure–property relations. The degree of nanowire alignment changed breaking stresses by a factor of 1.25 and the elongation at break by a factor of 2.75. Plasma annealing of the fiber to form a solid metal shell decreased the breaking stress by 65%.

We show that the use of oriented linear arrays of smectic A defects, the so-called smectic oily streaks, enables the orientation of gold nanorods (GNRs) for a large range of GNR diameters, ranging from 7 to 48 nm, and for various ligands. For the small GNRs it enables oriented end-to-end small chains of GNRs when the density is increased from around 2 GNRs/μm2 to around 6 GNRs/μm2. We have characterized the orientation of single GNRs by spectrophotometry and two-photon luminescence (TPL). A strongly anisotropic absorption of the composites and an on–off switching of GNR luminescence, both controlled by incident light polarization, are observed, revealing an orientation of the GNRs mostly parallel to the oily streaks. A more favorable trapping of GNRs by smectic dislocations with respect to ribbon-like defects is thus demonstrated. The dislocations appear to be localized at a specific localization, namely, the summit of rotating grain boundaries. Combining plasmonic absorption measurements, TPL measurements, and simulation of the plasmonic absorption, we show that the end-to-end GNR chains are both dimers and trimers, all parallel to each other, with a small gap between the coupled GNRs, on the order of 1.5 nm, thus associated with a large red-shift of 110 nm of the longitudinal plasmonic mode. A motion of the GNRs along the dislocations appears as a necessary ingredient for the formation of end-to-end GNR chains, the gap value being driven by the balance between the attracting van der Waals interactions and the steric repulsion between the GNRs and leading to interdigitation of the neighboring ligands. We thus obtain electromagnetic coupling of nanorods controlled by light polarization.

We study the molecular origins of anisotropy in a semicrystalline polymer nanocomposite that is caused by aligned, elongated filler nanoparticles. Our study is based on spatially resolved 2D WAXS/SAXS data that indicates the arrangement of molecules, lamellae, and filler particles in the composite. Isotactic polypropylene (IPP) samples filled with anisotropic TiO2 nanoparticles were prepared by injection molding. The nanocomposite contained IPP crystals with preferential alignment, while neat IPP formed crystals with random orientation under the same preparation conditions. We studied the mechanism through which anisotropic TiO2 nanoparticles change the molecular assembly in the polymer melt and cause preferential alignment. Our hypothesis is that shear forces during injection molding align the long axis of the nanoparticles parallel to the melt flow direction, and the particles align the adjacent IPP molecules. The aligned IPP molecules in the melt then serve as nuclei in crystal growth during solidification. This templating increases the elastic modulus compared to that of neat IPP.

An appropriate antibiotherapy is crucial for the safety and recovery of patients. Depending on the clinical conditions of patients, the required dose to effectively eradicate an infection may vary. An inadequate dosing not only reduces the efficacy of the antibiotic, but also promotes the emergence of antimicrobial resistances. Therefore, a personalized therapy is of great interest for improved patients' outcome and will reduce in long-term the prevalence of multidrug-resistances. In this context, on-site monitoring of the antibiotic blood concentration is fundamental to facilitate an individual adjustment of the antibiotherapy. Herein, we present a bioinspired approach for the bedside monitoring of free accessible ß-lactam antibiotics, including penicillins (piperacillin) and cephalosporins (cefuroxime and cefazolin) in untreated plasma samples. The introduced system combines a disposable microfluidic chip with a naturally occurring penicillin-binding protein, resulting in a high-performance platform, capable of gauging very low antibiotic concentrations (less than 6 ng ml-1) from only 1 μl of serum. The system's applicability to a personalized antibiotherapy was successfully demonstrated by monitoring the pharmacokinetics of patients, treated with ß-lactam antibiotics, undergoing surgery. © 2017 The Author(s).

Scaffold proteins are hubs for the coordination of intracellular signaling networks. The scaffold protein CNK1 promotes several signal transduction pathway. Here we demonstrate that sterile motif alpha (SAM) domain-dependent oligomerization of CNK1 stimulates CNK1-mediated signaling in growth factor-stimulated cells. We identified Ser22 located within the SAM domain as AKT-dependent phosphorylation site triggering CNK1 oligomerization. Oligomeric CNK1 increased the affinity for active AKT indicating a positive AKT feedback mechanism. A CNK1 mutant lacking the SAM domain and the phosphorylation-defective mutant CNK1S22A antagonizes oligomerization and prevents CNK1-driven cell proliferation and matrix metalloproteinase 14 promoter activation. The phosphomimetic mutant CNK1S22D constitutively oligomerizes and stimulates CNK1 downstream signaling. Searching the COSMIC database revealed Ser22 as putative target for oncogenic activation of CNK1. Like the phosphomimetic mutant CNK1S22D, the oncogenic mutant CNK1S22F forms clusters in serum-starved cells comparable to clusters of CNK1 in growth factor-stimulated cells. CNK1 clusters induced by activating Ser22 mutants correlate with enhanced cell invasion and binding to and activation of ADP ribosylation factor 1 associated with tumor formation. Mutational analysis indicate that EGF-triggered phosphorylation of Thr8 within the SAM domain prevents AKT binding and antagonizes CNK1-mediated AKT signaling. Our findings reveal SAM domain-dependent oligomerization by AKT as switch for CNK1 activation. © 2016 Elsevier B.V.

Recent advances in the development of light-inducible transgene expression systems have overcome many inherent drawbacks of conventional chemically regulated systems. The latest generation of those light-regulated systems that are specifically responsive to different wavelengths allows spatiotemporal control of gene expression in a so far unprecedented manner. In this chapter, we first describe the available light-inducible gene expression systems compatible with mammalian cells and explain their underlying mechanisms. Afterward, we give a detailed protocol for the implementation of a UVB light-inducible expression system in mammalian cells. © 2017, Springer Science+Business Media LLC.