Showing papers by "Stefan Seeger published in 2007"

A Comprehensive Study of Concepts and Phenomena of the Nonspecific Adsorption of β‐Lactoglobulin

Abstract: We investigate nonspecific protein adsorption processes by comparing experimentally measured adsorption kinetics of β-lactoglobulin with mathematical models. The adsorption and desorption behavior of this protein on a hydrophilic glass surface in citrate buffer (pH 3.0), monitored for a large set of different bulk concentrations (0.5×10−8 M–1.5×10−6 M) using a supercritical angle fluorescence (SAF) biosensor, is reported. Increasing adsorption rates and overshootings in the beginning of the adsorption are observed as well as a transition to an almost irreversibly bound state of the protein in the long term. Furthermore, rinsing experiments prove that adsorbed proteins abruptly change their desorption behavior from irreversible to reversible when a critical surface coverage θcrit is reached. Based on all experimental observations, a mathematical model composed of three adsorbed states differing in their surface affinity is proposed. Terms to account for lateral interactions between surface-bound proteins are included, which yield an excellent fit of the measured kinetics. For the first time, several phenomena that have been discussed in theoretical studies are confirmed by comparing experimental data with a single model.

Reactive magnetron sputtering of tungsten disulfide (WS2−x) films: Influence of deposition parameters on texture, microstructure, and stoichiometry

Abstract: Tungsten disulfide (WS2−x) films (0.07⩽x⩽0.7) were prepared by reactive magnetron sputtering from a tungsten target in rare gas/H2S atmospheres and at substrate temperatures up to 620°C. The nucleation and growth of the films were investigated by in situ energy dispersive x-ray diffraction (EDXRD) and by ex situ techniques such as electron microscopy, elastic recoil detection analysis, and x-ray reflectivity. From the EDXRD analysis it was found that the films always nucleate with the (001) planes, i.e., the van der Waals planes, parallel to the substrate surface. For high deposition rates and/or low substrate temperatures a texture crossover from the (001) to the (100) crystallite orientation occurs during the growth. High deposition rates, low substrate temperatures, or low sputtering pressures lead to a significant lattice expansion of the crystallites in the c direction (up to 3%). This is most probably caused by a disturbed or turbostratic film growth induced by the energetic bombardment during film ...

Parallel two-channel near- and far-field fluorescence microscopy.

Abstract: We report a new two-channel fluorescence microscopy technique for surface-generated fluorescence. The realized fluorescence microscope allows high resolution imaging of aqueous samples. The core element of the instrument is a parabolic mirror objective that is used to collect the fluorescence at large surface angles above the critical angle of the water/glass interface. An aspheric lens, incorporated into the solid parabolic element, is used for diffraction-limited laser focusing and for collecting fluorescence at low angles with respect to the optical axis. By separated collection of the fluorescence emitted into supercritical and subcritical angles, two detection volumes strongly differing in their axial resolution are generated at the surface of a glass cover slip. The collection of supercritical angle fluorescence (SAF) results in a strict surface confinement of the detection volume, whereas collecting below the critical angle allows gathering the fluorescence emitted several microns deep inside the sample. Consequently, the signals from surface-bound and unbound diffusing fluorescent molecules can be obtained simultaneously.

Ultrasensitive Staining-Free Protein Detection After PAA Gel Electrophoresis Using Deep UV Fluorescence

Abstract: We present the observation of separated protein bands after polyacrylamide (PAA) gel electrophoresis based on the staining-free detection of their ultra violet (UV)-induced fluorescence employing deep UV confocal fluorescence microscopy. Mixtures of the three biological compounds β-Galactosidase (from Escherichia coli), apo-Transferrin (bovine) and bovine serum albumin (BSA) have been separated and a staining free detection limit below 80 pg (7.0x108 molecules) per band has been achieved. This corresponds to ∼270 molecules in the detection volume for confocal microscopy.

Von der Innovationsflut zum wirtschaftlichen Erfolg

Abstract: Es werden Aspekte des Innovationsprozesses in jungen, kleinen und mittleren Unternehmen diskutiert, die auf kein institutionelles Innovationsmanagement zuruckgreifen konnen und denen ein gewisses chaotisches Innovieren unterstellt wird. Dazu werden Wege aufgezeigt, wie mit einfachen Mitteln Fehler und ihre zum Teil gravierenden Konsequenzen vermieden werden konnen. Die vorgeschlagenen Strukturen von Innovationsprozessen wurden in der Molecular Machines & Industries AG, Zurich, sehr erfolgreich implementiert. Entwicklungskosten und -verzogerungen konnten deutlich reduziert und die Flexibilitat signifikant erhoht werden.

Parallel two channel near and far field fluorescence microscopy

Abstract: We report a new two-channel fluorescence microscopy technique for surface-generated fluorescence. The realized fluorescence microscope allows high resolution imaging of aqueous samples. The core element of the instrument is a parabolic mirror objective that is used to collect the fluorescence at large surface angles above the critical angle of the waterglass interface. An aspheric lens, incorporated into the solid parabolic element, is used for diffraction-limited laser focusing and for collecting fluorescence at low angles with respect to the optical axis. By separated collection of the fluorescence emitted into supercritical and subcritical angles, two detection volumes strongly differing in their axial resolution are generated at the surface of a glass cover slip. The collection of supercritical angle fluorescence (SAF) results in a strict surface confinement of the detection volume, whereas collecting below the critical angle allows gathering the fluorescence emitted several microns deep inside the sample. Consequently, the signals from surface-bound and unbound diffusing fluorescent molecules can be obtained simultaneously.