Herstellung von Oligomeren aus Nano-Kugeln und deren Charakterisierung

Plasmonische Nano-Strukturen bieten durch ihre Eigenschaften als optische Antennen und aufgrund der hohen geometrischen Vielfalt diverse Anwendungsmöglichkeiten in verschiedenen Gebieten der Sensorik. Die in dieser Dissertation gezeigten Oligomere sind Superstrukturen, die aus Nano-Kugeln zusammengesetzt sind. Diese haben spezielle Eigenschaften, die zunächst theoretisch gezeigt werden. Um die optischen Eigenschaften der Strukturen zu messen, wurde ein Messaufbau entwickelt, der eine automatisierte Aufnahme von Spektren ermöglicht und die Reproduzierbarkeit der Messungen optimiert. Die Oligomere wurden dazu auf zwei unterschiedliche Arten hergestellt, beginnend mit der kapillaren Anordnung kolloidaler Gold-Kugeln auf einem vorstrukturierten Substrat. Damit wurden Oligomere mit unterschiedlicher Geometrie und Anzahl an Kugeln fabriziert. Die strukturelle Untersuchung der Proben wurde mit einem Rasterelektronenmikroskop (REM) durchgeführt, Dunkelfeldspektren wurden mit dem zuvor beschriebenen Aufbau aufgenommen. Zusätzlich wurden Messungen der oberflächenverstärken Raman-Streuung (SERS) durchgeführt. Hierbei konnte keine Korrelation zwischen den Dunkelfeldspektren und der SERS-Verstärkung gefunden werden. Zur Optimierung der Oberflächenrauigkeit und der Anordnung der Oligomere wurde ein rein auf Elektronenstrahllithographie (ESL) basierender Prozess entwickelt. Hierbei werden mittels ESL Lochpaare in einer hohen Lackschicht erzeugt und durch zweimaliges Aufdampfen von Gold entstehen Nano-Säulen, die nach dem Entfernen der Lackschicht durch schnelles Erhitzen schmelzen und Kugelform annehmen. Da das Volumen während des Schmelzvorgangs konstant bleibt, besitzen die Kugeln einen größeren Radius als die Säulen. Somit kann der Abstand eines Säulenpaares durch das Schmelzen verringert werden, und es ist möglich, Oligomere mit sehr kleinem Abstand herzustellen. Dieser wurde mithilfe von REM-Aufnahmen vermessen und es wurden ebenfalls Dunkelfeldspektren aufgenommen. Die Interpretation der Dunkelfeldspektren wurde durch die Simulation der optischen Eigenschaften der Dimere unterstützt und es zeigt sich ein exponentieller Zusammenhang zwischen dem Abstand der Dimere und der spektralen Position der fundamentalen Resonanz

Ligand-induced epitope masking. Dissociation of integrin α5β1-fibronectin complexes only by monoclonal antibodies with an allosteric mode of action.

We previously demonstrated that Arg-Gly-Asp (RGD)-containing ligand-mimetic inhibitors of integrins are unable to dissociate pre-formed integrin-fibronectin complexes (IFCs). These observations suggested that amino acid residues involved in integrin-fibronectin binding become obscured in the ligand-occupied state. Because the epitopes of some function-blocking anti-integrin monoclonal antibodies (mAbs) lie near the ligand-binding pocket, it follows that the epitopes of these mAbs may become shielded in the ligand-occupied state. Here, we tested whether function-blocking mAbs directed against α5β1 can interact with the integrin after it forms a complex with an RGD-containing fragment of fibronectin. We showed that the anti-α5 subunit mAbs JBS5, SNAKA52, 16, and P1D6 failed to disrupt IFCs and hence appeared unable to bind to the ligand-occupied state. In contrast, the allosteric anti-β1 subunit mAbs 13, 4B4, and AIIB2 could dissociate IFCs and therefore were able to interact with the ligand-bound state. However, another class of function-blocking anti-β1 mAbs, exemplified by Lia1/2, could not disrupt IFCs. This second class of mAbs was also distinguished from 13, 4B4, and AIIB2 by their ability to induce homotypic cell aggregation. Although the epitope of Lia1/2 was closely overlapping with those of 13, 4B4, and AIIB2, it appeared to lie closer to the ligand-binding pocket. A new model of the α5β1-fibronectin complex supports our hypothesis that the epitopes of mAbs that fail to bind to the ligand-occupied state lie within, or very close to, the integrin-fibronectin interface. Importantly, our findings imply that the efficacy of some therapeutic anti-integrin mAbs could be limited by epitope masking

Single particle dark-field spectroscopy of spherical dimers with down to sub-10 nm gaps fabricated by the annealing of nano-pillars

In this paper we present a method for the fabrication of plasmonic spherical dimers and oligomers with narrow gaps and tunable distances. High-aspect-ratio nano-pillars are created by the two-step evaporation of gold on structured substrates. By using electron beam lithography, it is possible to control the close spacing of the pillars. Rapid thermal annealing causes the pillars to adopt a spherical shape. Since by melting the spheres gain in diameter compared to the initial nano-pillars, the distance between two adjacent spheres can be reduced to below 10 nm. Dimers with different distances were fabricated and optically characterized by single particle dark-field spectroscopy. The characteristic red-shift of the longitudinal mode due to stronger coupling for smaller distances could be clearly observed and follows a general scaling behavior

BEMER Electromagnetic Field Therapy Reduces Cancer Cell Radioresistance by Enhanced ROS Formation and Induced DNA Damage.

Each year more than 450,000 Germans are expected to be diagnosed with cancer subsequently receiving standard multimodal therapies including surgery, chemotherapy and radiotherapy. On top, molecular-targeted agents are increasingly administered. Owing to intrinsic and acquired resistance to these therapeutic approaches, both the better molecular understanding of tumor biology and the consideration of alternative and complementary therapeutic support are warranted and open up broader and novel possibilities for therapy personalization. Particularly the latter is underpinned by the increasing utilization of non-invasive complementary and alternative medicine by the population. One investigated approach is the application of low-dose electromagnetic fields (EMF) to modulate cellular processes. A particular system is the BEMER therapy as a Physical Vascular Therapy for which a normalization of the microcirculation has been demonstrated by a low-frequency, pulsed EMF pattern. Open remains whether this EMF pattern impacts on cancer cell survival upon treatment with radiotherapy, chemotherapy and the molecular-targeted agent Cetuximab inhibiting the epidermal growth factor receptor. Using more physiological, three-dimensional, matrix-based cell culture models and cancer cell lines originating from lung, head and neck, colorectal and pancreas, we show significant changes in distinct intermediates of the glycolysis and tricarboxylic acid cycle pathways and enhanced cancer cell radiosensitization associated with increased DNA double strand break numbers and higher levels of reactive oxygen species upon BEMER treatment relative to controls. Intriguingly, exposure of cells to the BEMER EMF pattern failed to result in sensitization to chemotherapy and Cetuximab. Further studies are necessary to better understand the mechanisms underlying the cellular alterations induced by the BEMER EMF pattern and to clarify the application areas for human disease

Mapping of plasmonic resonances in nanotriangles

Plasmonic resonances in metallic nano-triangles have been investigated by irradiating these structures with short laser pulses and imaging the resulting ablation and melting patterns. The triangular gold structures were prepared on Si substrates and had a thickness of 40 nm and a side length of ca. 500 nm. Irradiation was carried out with single femtosecond and picosecond laser pulses at a wavelength of 800 nm, which excited higher order plasmon modes in these triangles. The ablation distribution as well as the local melting of small parts of the nanostructures reflect the regions of large near-field enhancement. The observed patterns are reproduced in great detail by FDTD simulations with a 3-dimensional model, provided that the calculations are not based on idealized, but on realistic structures. In this realistic model, details like the exact shape of the triangle edges and the dielectric environment of the structures are taken into account. The experimental numbers found for the field enhancement are typically somewhat smaller than the calculated ones. The results demonstrate the caveats for FDTD simulations and the potential and the limitations of “near field photography” by local ablation and melting for the mapping of complex plasmon fields and their applications

Self-assembled quasi-hexagonal arrays of gold nanoparticles with small gaps for surface-enhanced Raman spectroscopy

The fabrication and optical characterization of self-assembled arrangements of rough gold nanoparticles with a high area coverage and narrow gaps for surface-enhanced Raman spectroscopy (SERS) are reported. A combination of micellar nanolithography and electroless deposition (ED) enables the tuning of the spacing and size of the noble metal nanoparticles. Long-range ordered quasi-hexagonal arrays of gold nanoparticles on silicon substrates with a variation of the particle sizes from about 20 nm to 120 nm are demonstrated. By increasing the particle sizes for the homogeneously spaced particles, a large number of narrow gaps is created, which together with the rough surface of the particles induces a high density of intense hotspots. This makes the surfaces interesting for future applications in near-field-enhanced bio-analytics of molecules. SERS was demonstrated by measuring Raman spectra of 4-MBA on the gold nanoparticles. It was verified that a smaller inter-particle distance leads to an increased SERS signal

Mapping of plasmonic resonances in nanotriangles

Plasmonic resonances in metallic nano-triangles have been investigated by irradiating these structures with short laser pulses and imaging the resulting ablation and melting patterns. The triangular gold structures were prepared on Si substrates and had a thickness of 40 nm and a side length of ca. 500 nm. Irradiation was carried out with single femtosecond and picosecond laser pulses at a wavelength of 800 nm, which excited higher order plasmon modes in these triangles. The ablation distribution as well as the local melting of small parts of the nanostructures reflect the regions of large near-field enhancement. The observed patterns are reproduced in great detail by FDTD simulations with a 3-dimensional model, provided that the calculations are not based on idealized, but on realistic structures. In this realistic model, details like the exact shape of the triangle edges and the dielectric environment of the structures are taken into account. The experimental numbers found for the field enhancement are typically somewhat smaller than the calculated ones. The results demonstrate the caveats for FDTD simulations and the potential and the limitations of “near field photography” by local ablation and melting for the mapping of complex plasmon fields and their applications