Publikationen

The size of gold nanoparticles (AuNPs) can influence various aspects of their cellular uptake. Light microscopy is not capable of resolving most AuNPs, while electron microscopy (EM) is not practically capable of acquiring the necessary statistical data from many cells and the results may suffer from various artifacts. Here, we demonstrate the use of a fast EM method for obtaining high-resolution data from a much larger population of cells than is usually feasible with conventional EM. A549 (human lung carcinoma) cells were subjected to uptake protocols with 10, 15, or 30 nm diameter AuNPs with adsorbed serum proteins. After 20 min, 24 h, or 45 h, the cells were fixed and imaged in whole in a thin layer of liquid water with environmental scanning electron microscopy equipped with a scanning transmission electron microscopy detector. The fast preparation and imaging of 145 whole cells in liquid allowed collection of nanoscale data within an exceptionally small amount of time of ~80 h. Analysis of 1,041 AuNP-filled vesicles showed that the long-term AuNP storing lysosomes increased their average size by 80 nm when AuNPs with 30 nm diameter were uptaken, compared to lysosomes of cells incubated with AuNPs of 10 and 15 nm diameter.

Scanning transmission electron microscopy (STEM) of specimens in liquid is possible using a microfluidic chamber with thin silicon nitride windows. This paper includes an analytic equation of the resolution as a function of the sample thickness and the vertical position of an object in the liquid. The equipment for STEM of liquid specimen is briefly described. STEM provides nanometer resolution in micrometer-thick liquid layers with relevance for both biological research and materials science. Using this technique, we investigated tagged proteins in whole eukaryotic cells, and gold nanoparticles in liquid with time-lapse image series. Possibly future applications are discussed. / La microscopie électronique à balayage en transmission (STEM) d'échantillons immergés dans un liquide est possible en utilisant une chambre microfluidique réalisée avec de fines fenêtres en nitrure de silicium. Cet article introduit d'abord une équation analytique permettant d'estimer la résolution spatiale accessible en fonction de l'épaisseur totale de l'échantillon et de la position de l'objet d'intérêt en son sein. Après une description brève de l'équipement utilisable, nous montrons comment cette approche STEM permet d'observer avec une résolution nanométrique des objets d'intérêt en biologie ou en science des matériaux, plongés dans une couche liquide de plusieurs micromètres d'épaisseur. Avec cette technique, nous avons étudié la distribution de protéines marquées dans des cellules eucaryotes complètes et celle dynamique de nanoparticules d'or dans un liquide au moyen de séries d'images résolues en temps. Enfin, nous proposons quelques grands axes pour de futures applications.

Fundamental parameters influencing the ion-producing efficiency of palladium nanostructures (nanoparticles [Pd-NP], nanoflowers, nanofilms) during laser irradiation were studied in this paper. The nanostructures were immobilized on the surface of different solid inorganic carrier materials (porous and mono-crystalline silicon, anodic porous aluminum oxide, glass and polished steel) by using classical galvanic deposition, electroless local deposition and sputtering. It was the goal of this study to investigate the influence of both the nanoparticular layer as well as the carrier material on ion production for selected analyte molecules. Our experiments demonstrated that the dimensions of the synthesized nanostructures, the thickness of the active layers, surface disorders, thermal conductivity and physically or chemically adsorbed water influenced signal intensities of analyte ions during surface-assisted laser desorption/ionization (SALDI) while no effects such as plasmon resonance, photoelectric effect or catalytic activity were expected to occur. Excellent LDI abilities were seen for Pd-NPs immobilized on steel, while Pd nanoflowers on porous silicon exhibited several disadvantages; viz, strong memory effects, dependency of the analytical signal on amount of physically and chemically adsorbed water inside porous carrier, reduced SALDI activity from unstable connections between Pd and semiconductor material, decrease of the melting point of pure silicon after Pd immobilization and resulting strong laser ablation of metal/semiconductor complex, as well as significantly changed surface morphology after laser irradiation. The analytical performance of Pd-NP/steel was further improved by applying a hydrophobic coating to the steel surface before galvanic deposition. This procedure increased the distance between Pd-NPs, thus reducing thermal stress upon LDI; it simultaneously decreased spot sizes of deposited sample solutions.

A simple approach for synthesis of palladium and silver nanostructures with readily adjustable morphologies was developed using galvanic electrochemical deposition, for application to surface-assisted laser desorption/ionization (SALDI) of small biological molecules. A range of fatty acids, triglycerides, carbohydrates, and antibiotics were investigated to assess the performance of the new materials. Intense analyte cations were generated from the galvanic surfaces upon UV laser irradiation such as potassium adducts for a film thickness <100 nm (originating from impurities of the electrolyte solution) and Pd and Ag cluster ions for films with a thickness >120 nm. Possible laser desorption/ionization mechanisms of these galvanic structures are discussed. The films exhibited self-organizing abilities and adjustable morphologies by changing electrochemical parameters. They did not require any stabilizing agents and were inexpensive and very easy to produce. SALDI analysis showed that the materials were stable under ambient conditions and analytical results with excellent measurement reproducibility and detection sensitivity similar to MALDI were obtained. Finally, we applied the galvanic surfaces to fast screening of natural oils with minimum sample preparation.

The anisotropy of friction on graphitic surfaces is investigated by a combined friction force microscopy and modeling study. Friction vectors deviate up to 15° from pulling directions. The strongest deviations are found for pulling directions which lie almost along one zigzag direction of the honeycomb structure, the preferred sliding direction on graphite surfaces and epitaxial graphene grown on SiC(0001). Atomic stick-slip events along and across molecular rows determine direction and magnitude of friction. Simulation and modeling reveal the role of temperature and of the two-dimensional character of the surface potential for the friction anisotropy.

We describe an interdisciplinary class offered to undergraduate university students of Arts and Sciences, with most participants majoring in philosophy or physics. The class combines learning about the theory of atomic force microscopes (AFMs), using them for gathering data and processing images out of the data in hands-on exercises with (1) understanding important do's and don'ts of image processing and (2) with philosophical reflection on microscopy and image theory guided by philosophers' texts, written between 1690 and 2010, on microscopes, on images and on the suitable-realist or antirealist-interpretation of microscopic images.

Friction involves a complex set of phenomena spanning a large range of length scales, but experiments assessing the evolution of the slip-front between two dry sliding bodies now reveal that slip can be reasonably well described by linear fracture mechanics theory.

Reibung lässt sich elektrochemisch kontrollieren. Mit ionischen Flüssigkeiten elektrochemisch gesteuerte Reibvorgänge könnten in kleinskaligen, miniaturisierten Kontakten herkömmliche Schmiermittel ersetzen.

The mechanical properties of the ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py1,4][FAP]) in confinement between a SiOx and a Au(1 1 1) surface are investigated by means of atomic force microscopy (AFM) under electrochemical control. Up to 12 layers of ion pairs can be detected through force measurements while approaching the tip of the AFM to the surface. The particular shape of the force versus distance curve is explained by a model for the interaction between tip, gold surface and ionic liquid, which assumes an exponentially decaying oscillatory force originating from bulk liquid density correlations. Jumps in the tip-sample distance upon approach correspond to jumps of the compliant force sensor between branches of the oscillatory force curve. Frictional force between the laterally moving tip and the surface is detected only after partial penetration of the last double layer between tip and surface.

We study nanoindentation and scratching of graphene-covered Pt(111) surfaces in computer simulations and experiments. We find elastic response at low load, plastic deformation of Pt below the graphene at intermediate load, and eventual rupture of the graphene at high load. Friction remains low in the first two regimes, but jumps to values also found for bare Pt(111) surfaces upon graphene rupture. While graphene substantially enhances the load carrying capacity of the Pt substrate, the substrate's intrinsic hardness and friction are recovered upon graphene rupture.