FRET Studies of the Interaction of Dimeric Cyanine Dyes with DNA

Fluorescence Resonance Energy Transfer (FRET) is a powerful tool to determine distances between chromophores bound to macromolecules, since the efficiency of the energy transfer from an initially excited donor to an acceptor strongly depends on the distance between the two dye molecules. The structure of the noncovalent complex of double-strand DNA (dsDNA) with thiazol orange dimers (TOTO) allows FRET analysis of two intercalated chromophores. By intercalation of two different TOTO dyes we observe an energy transfer from TOTO-1 as donor and TOTO-3 as acceptor. In this manner we are able to determine the mean distance between two proximate TOTO molecules bound to dsDNA. Thus the maximum number of binding positions for this type of intercalation dyes in the dsDNA can be obtained. Furthermore the dependency of the acceptor emission on the donor concentration is analysed. The emission of TOTO-3 reaches a maximum when the acceptor-to-donor ratio is 1:1

Droplet Memory on Liquid-Infused Surfaces

The knowledge of droplet friction on liquid-infused surfaces (LIS) is of paramount importance for applications involving liquid manipulation. While the possible dissipation mechanisms are well-understood, the effect of surface texture has thus far been mainly investigated on LIS with highly regular solid topographies. In this work, we aim to address this experimental gap by studying the friction experienced by water droplets on LIS based on both random and regular polysilsesquioxane nanostructures. We show that the available models apply to the tested surfaces, but we observe a previously unreported droplet memory effect: as consecutive droplets travel along the same path, their velocity increases up to a plateau value before returning to the original state after a sufficiently long time. We study the features of this phenomenon by evaluating the motion of droplets when they cross the path of a previous sequence of droplets, discovering that moving droplets create a low-friction trace in their wake, whose size matches their base diameter. Finally, we attribute this to the temporary smoothing out of an initially conformal lubricant layer by means of a Landau–Levich–Derjaguin liquid film deposition behind the moving droplet. The proposed mechanism might apply to any LIS with a conformal lubricant layer

Tax revenue accruing from the commercialization of research findings as an indicator for economic benefits of government financed research

In this article, we propose the use of tax payments accruing from the commercialization of research findings as a measure of research benefits complementing the existing range of evaluation tools. We place this novel approach to assess the economic returns to publicly funded research in the context of previous studies and highlight its advantages. The application of our method over a long period is demonstrated with the example of saccharin, which was discovered in the context of a curiosity-driven fundamental research project. In our study, we focused on Monsanto's commercial saccharin production finding notable return

Micropatterning of superhydrophobic silicone nanofilaments by a near-ultraviolet Nd:YAG laser

We demonstrate that a recently developed coating composed of superhydrophobic silicone nanofilaments can be selectively functionalized to yield well defined micron-scale patterns of contrasting wettabilities (superhydrophobic/hydrophilic and amphiphobic/amphiphilic). Nanofilament ablation was performed using a near-ultraviolet (UV) laser with a wavelength of 355 nm and a repetition rate of 10 kHz. This is a highly promising approach for open channel microfluidics and microarray analysis due to its simplicity, the chemical and environmental stability of the coating, and the low cos

Multiplextest zum Nachweis verschiedener Tumorantigene an einer Karzinomzelllinie durch zeitaufgelöste Einzelphotonenzählung

Tumorzellen tragen für sie charakteristische Antigene, sogenannte Tumorantigene, die sie von anderen Zellen unterscheiden und daher ein Merkmal für die Diagnostik darstellen. Für die Therapie spielen diese Tumorantigene zunehmend eine wichtige Rolle, weil sie eine spezifische Angriffsstelle für Antikörper bieten, die diese Zellen über eine Antikörper-Antigenkopplung markieren und somit für das Immunsystem erkennbar machen. Je detaillierter die Charakterisierung eines Tumors (Tumorheterogenität, Expressionsdichte der Tumorantigene) in Bezug auf solche Antigene z. B. membranständige Rezeptoren erfolgt, desto spezifischer könnten zukünftige Therapien auf den Patienten individuell abgestimmt werden. Für einen möglichst effizienten und exakten quantitativen Nachweis verschiedener Antigene an einem Tumorgewebeschnitt bietet die Methode der zeitaufgelösten Einzelphotonenzählung TCSPC (Time Correlated Single Photon Counting) in Kombination mit verschiedenen Farbstofflabels eine interessante Alternative zu herkömmlichen Verfahren. Diese Art des fluoreszenten Nachweises kombiniert die Vorteile des konfokalen Laserscanning-Mikroskops mit denen eines Multilabeltests. Für den Fluoreszenznachweis eines Antigens wird der dazu komplementäre Antikörper mit einem Farbstoff gekoppelt. Möchte man verschiedene Antigene an einem biologischen System gleichzeitig detektieren, so muss jeder spezifisch bindende Antikörper mit einem anderen Farbstoff konjugiert werden. Dieser kann sich in seiner Emissionswellenlänge von den anderen unterscheiden, der Fluoreszenznachweis erfolgt dann über geeignete optische Filtersysteme. Bei der TCSPC-Messung ist die charakteristische Messgröße die Fluoreszenzlebensdauer des am Antikörper gekoppelten Farbstoffs. Alle Farbstoffe werden mit derselben monochromatischen Lichtquelle zur Fluoreszenz angeregt und emittieren in dasselbe Wellenlängenfenster

Reduced bacterial colonisation on surfaces coated with silicone nanostructures

Bacterial adhesion on silicone nano- and microstructures is investigated in stagnant and flow experiments. Static adhesion tests are performed in 0.9% NaCl solution. These experiments reveal that the number of Staphylococcus epidermidis (S. epidermidis) and Escherichia coli (E. coli) adhering to glass surfaces can significantly be reduced if silicone nanofilament and rod coatings are present. Further, flow experiments are conducted in a parallel-plate flow chamber using 0.9% NaCl solution and artificial urine as medium. Silicone nanofilament coated surfaces are compared to uncoated glass surfaces. E. coli colonisation on filament coated surfaces is reduced for at least 24 h in 0.9% NaCl solution, while in artificial urine no reduction is observed after 24 h. S. epidermidis shows converse adhesion behaviour. Here, initial adhesion on nanofilaments is promoted but the number of adherent S. epidermidis seems to decrease after extended contact time. The obtained results demonstrate that superhydrophobic silicone surfaces significantly reduce bacterial colonisation under stagnant and dynamic conditions. However, the bacterial adhesion behaviour depends on the architecture of the silicone nano- and microstructures and the bacterial species investigated

Preparation and characterization of layered dichalcogenides MoS2 and WS2 for photovoltaic applications

Die halbleitenden Schichtgittersulfide MS2 (M=Mo, W) mit direkten Bandlücken Eg=1,8 eV und hohen Absorptionskoeffizienten (105cm-1 (2 eV)) sind als Absorbermaterialien in Dünnschichtsolarzellen interessant. Die van-der-Waals (vdW)-Oberfläche in diesen Schichtgitterhalbleitern (parallel zur Basalebene) zeichnet sich durch geringe Konzentrationen an Oberflächenzuständen aus und bildet damit eine ideale Voraussetzung zur Bildung von elektronisch hochwertigen Grenzflächen in p-n-Heteroübergängen. Für polykristalline WSx-Schichten leitet sich daraus die Forderung ab, dass das Wachstum von großen Kristalliten mit der vdW-Oberfläche parallel zum Substrat ((001)-Textur) von Vorteil ist. In dieser Arbeit wurde die Anwendbarkeit des reaktiven Magnetronsputterns zur Herstellung von (001)-texturierten polykristallinen WSx-Schichten untersucht. Hierfür wurde eine Magnetronsputterquelle mit einem Wolframtarget und eine Gasmischung aus Argon und H2S verwendet. Die strukturellen, elektrischen und optischen Eigenschaften der gesputterten WSx-Schichten wurden in Abhängigkeit von den Prozessparametern studiert. In situ energiedispersive Röntgenbeugung (EDXRD) an der Synchrotronstrahlungsquelle im HASYLAB in Hamburg (DESY) wurde benutzt, um das Wachstum der WSx-Schichten während des Sputterprozesses zu untersuchen. Diese Untersuchungen haben ergeben, dass WSx-Schichten bei hoher Substrattemperatur (Ts=620°C), hohem Totalgasdruck (p < 1 Pa) und hoher Plasmaanregungsfrequenz (27,12 MHz) in einer (001)-Textur auf oxidierten Silizium und Quarzglas wachsen. Bei diesen Prozessparametern ist der Beschuss der wachsenden Schicht mit energetischen Ionen während des Magnetronsputterns reduziert. Obwohl sich diese Schichten durch gute strukturelle Eigenschaften auszeichnen, ergaben die elektrischen und optischen Charakterisierungen, dass die photo-elektrische Qualität für eine Anwendung als Absorbermaterial noch nicht ausreichend ist. In diesem Material führt schon der Beschuss mit niederenergetischen Ionen (Energie kleiner als 50 eV) während des Magnetronsputterns zu einem gestörten Schichtwachstum. Als Ursache werden hierfür die schwachen van-der-Waals-Wechselwirkungen zwischen den Schwefelatomen benachbarter (S-W-S)-Ebenen gesehen.The layered semiconducting dichalcogenides MS2 (M=Mo,W) with band gaps of about Eg1.8 eV and high absorption coefficients (105cm-1 (2 eV)) are of interest as absorber materials in solar energy conversion devices. The van der Waals (vdW) surface of the layered semiconductors (parallel to basal plane) are ideal for forming p-n heterojunctions because of the absence of inherent surface states arising from unsaturated bonds. Due to high levels of recombination at the edge planes ((100)-texture) it is required to produce polycrystalline films with large grains with their basal plane orientation parallel to the substrate ((001)-texture). In this work the suitability of reactive magnetron sputtering for preparing (001)-textured polycrystalline WSx films were explored. Commercial magnetron sputtering sources with tungsten targets in a mixture of argon and H2S were used. These films were investigated with respect to the change in film structure, chemical composition and optical and electrical properties in dependence of the sputtering conditions. In situ energy dispersive X-ray diffraction (EDXRD) at the synchrotron radiation source HASYLAB in Hamburg (Germany) was used to study the growth of the reactively sputtered films. It is shown that the films with a (001)-texture were grown at high temperatures (Ts=620°C), high sputtering pressures (p < 1Pa) and high plasma excitation frequency (27.12 MHz) on oxidized silicon or quartz glass. These conditions correspond to a low energetic particle bombardment of the growing films. In spite of the high crystallographic quality these WSx films exhibit a significant sulphur (x=1.85) deficit, a high defect density and impurity incorporation up to 3 atomic percent, which render these films unsuitable for photovoltaic applications. In conclusion it is shown that a quite low energy of ions (lesser than 50 eV) impinging the films is sufficient to disturb the growth of the WSx films during the deposition by magnetron sputtering, which is due to the weak bonding in this material

Travel times in the vadose zone : Variability in space and time

Peer reviewedPublisher PD

Sizing of single fluorescently stained DNA fragments by scanning microscopy

We describe an approach to determine DNA fragment sizes based on the fluorescence detection of single adsorbed fragments on specifically coated glass cover slips. The brightness of single fragments stained with the DNA bisintercalation dye TOTO‐1 is determined by scanning the surface with a confocal microscope. The brightness of adsorbed fragments is found to be proportional to the fragment length. The method needs only minute amount of DNA, beyond inexpensive and easily available surface coatings, like poly‐l‐lysine, 3‐aminoproyltriethoxysilane and polyornithine, are utilizable. We performed DNA‐sizing of fragment lengths between 2 and 14 kb. Further, we resolved the size distribution before and after an enzymatic restriction digest. At this a separation of buffers or enzymes was unnecessary. DNA sizes were determined within an uncertainty of 7-14%. The proposed method is straightforward and can be applied to standardized microtiter plate