Showing papers by "Stefan Seeger published in 1998"

Counting of single protein molecules at interfaces and application of this technique in early-stage diagnosis.

Abstract: The fluorescence-based detection and counting of single protein molecules after specific binding to antibodies at interfaces is presented. A diode laser was used as the excitation source. The unspecific binding at the interface has been reduced to a level of only 0.1% of the maximum signal level. At present, the detection limit of this molecule-counting process is in the range of 10-17 mol/L, and the dynamic range of the signal corresponds to 7 orders of magnitude of antigen concentration, but these values are not limiting. As a preliminary application in early-stage diagnosis, we have investigated the detection of a single cardiac actin molecule in human plasma, which is of interest in myocardial infarction diagnosis.

Immobilization of Biomolecules on Langmuir−Blodgett Films of Regenerative Cellulose Derivatives

Abstract: We present a new and fast method for preparation of ultrathin layers of biomolecules on solid substrates and its application as a useful tool for sensing biomolecules in an affinity biosensor. Nonamphiphilic trimethylsilyl ether−cellulose monolayers are used as interfaces to reduce nonspecific interactions between solid surfaces and biomolecules. These films are transferred on optical waveguides by the Langmuir−Blodgett technique. After their stabilization by cleavage of the hydrophobic trimehylsilyl groups, the cellulose films serve as excellent matrixes for the immobilization of proteins at high density. Cyanurchloride serves as a cross-linker between the cellulose layer and the proteins. The activity and biological specificity of these interfaces is controlled by an enzymatic assay and direct sensing by an evanescent wave immunosensor.

Static Magnetic Hyperfine Fields in Magnetically Polarized Pd

Abstract: In magnetically polarized ultrathin Pd films with (111) orientation, grown on a Ni(001) single crystal, static magnetic hyperfine fields were measured at the interface using perturbed angular correlation spectroscopy. The structural arrangement of the Pd atoms with respect to the Ni substrate differs from one Pd atom to the next, leading to varying $3d\ensuremath{-}4d$ electron hybridizations. This gives rise to a broad distribution of magnetic hyperfine fields at Rh nuclei, seen in experiments with the self-element probe ${}^{100}\mathrm{Pd}{/}^{100}\mathrm{Rh}$, while discrete field values were found for the voluminous impurity probe ${}^{111}$Cd.

Optical tweezers in pharmacology

Abstract: Current applications of optical tweezers in pharmacology are presented. The manufacture of cellular biosensor arrays employing optical tweezers is reviewed. Using this technique, a new approach to cellular drug screening, based on single cells patterned with the laser tweezers was introduced. Specific stimulation of different immobilized, viable cells could be shown simultaneously. Furthermore, the usefulness of optical tweezers for analyzing the interactions of ligands with cellular membrane receptors is demonstrated. The laser tweezers could successfully be used to compare neuron interactions with glycoproteins of the extracellular matrix by applying the optical tweezers as picotensometer. The forces of interactions between polystyrene beads coated with different proteins of the extracellular matrix and the cell membrane receptors of cerebellar neurons from postnatal day 6 (P6) mice were measured. When antibodies to the extracellular matrix proteins were added, forces were significantly reduced for the corresponding antigens but not for the other glycoproteins. This proved the specificity of the measured interactions. Information regarding the receptor anchorage of tenascin-C could be deduced.

Correlation between local magnetic and structural properties at the ni/pd interface

Abstract: High-energetic protons produce a multitude of short-lived radioactive products in nuclear spallation reactions. The on-line mass separator ISOLDE/CERN is designed to produce radioactive beams extracted from thick targets hit by 1 GeV protons from the PS-Booster accelerator. After ionization, the products or their radioactive daughters are extracted by high voltage, mass separated, and thus transformed into specific ion beams. By this procedure a variety of suitable probe nuclei is obtained (out of a total of 600 different isotopes) for the use in solid state physics involving nuclear methods such as perturbed angular correlation (PAC). The UHV chamber ASPIC (Apparatus for Surface Physics and Interfaces at CERN) at the UHV beamline of ISOLDE serves for an extremely clean deposition of these mass-separated probe atoms on precleaned surfaces. Here we report on magnetic hyperfine interactions observed with 111mCd/111Cd probe atoms positioned at the interface of Ni/Pd.

Aminoalkyl trialkyl silyl cellulose and a method for coating surfaces

Abstract: The invention relates to polysaccharide derivatives containing a) at least one hydrophobic agent and b) at least one substituent containing nitrogen. The derivative is especially a cellulose ether which, contains as a substituent, a) a trialkyl silyl group and b) an aminoalkyl group. The invention also relates to a method for immobilizing biomolecules on a flat coated carrier material on or in which the biomolecules are bound and said flat carrier material with a coated surface contains at least one such polysaccharide derivative inside or outside the coating. In addition, a barely soluble or insoluble reactive aminoalkane derivative which is contained in said solvent is added in the method for producing the mixed cellulose ether in a solution of trialkyl silyl cellulose in an organic solvent. The reaction is then carried out and the final product is isolated.

High efficiency optical system detecting light from e.g. excited marked biomolecules

Abstract: One plane end face of an optical element (1) faces the sample, interfacing with the sample medium, or with an intervening medium of higher optical density. All light emitted from the sample not deflected by total internal reflection, enters the optical element, including transiently radiated light. Once inside the element, all light is reflected through the second end face (4) onto a detector (30). The excitation light beam is seen to pass axially through the equipment, to be trapped by the absorber (27). Scattered and evanescent light (7) undergoes total internal reflection at the paraboloidal walls of the optical element, before being focused (29) onto the detector (30). The sample is situated at the focus of the element, a paraboloidal reflector, an arrangement capturing a maximum of emitted light.

Detection of single protein molecules at interfaces after antibody-antigen binding

Abstract: The fluorescence-based detection of single dye labeled protein molecules at interfaces is presented Glass substrates with covalent immobilized antibodies serve for capturing matching antigens from volume concentrations between 10-12 and 10-17 mol/l The unspecific binding at the interface has been reduced to a level down to 01% of the maximum signal level At concentrations lower than 10-13 mol/l we observe single antibody-antigen complexes at the surface We developed a scanning method for counting single antibody- antigen complexes The counting results are used for calibrating the volume concentration dependency AT the present stage, the detection limit of this molecule counting process is of the order of 10-17 mol/l, and the dynamic range detectable antigen concentration is more than 8 orders of magnitude, without reaching a limiting value The instrumental set-up is similar to that of a confocal microscope A diode laser is used as an excitation source As an first application in early-stage-diagnostics, we investigated the detection of a single cardiac-actin molecule in human plasma© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only

Optical tweezers as a tool for the functional analysis of neuronal cell membrane receptors

Abstract: Recognition molecules play important regulatory roles during pattern formation of the nervous system. We here show that optical tweezers can successfully be used to functionally and quantitatively compare neuron interactions with glycoproteins of the extracellular matrix. We measured the forces of interactions between tenascin-C, laminin-1 and fibronectin coated polystyrol beads and the cell membranes of different nervous cell-types. This was achieved by applying the optical tweezers as picotensometer to pull the adhering beads with varying axial forces. To this aim, the minimal laser powers for capturing polystyrene beads in different solutions were measured. With the corresponding Archimedes Forces the acting forces in the range of pN were calculated. The glycoproteins showed significantly different behavior. Specific binding was shown by antibody experiments, in which the binding forces were significantly reduced for the corresponding antigens but not for the other glycoproteins. Together with experiments concerning the moving within the plane of the membrane and the cleavage with glycosyl-phosphatidyl-inositol-anchors specific phospholipase-C we suggest that these glycoproteins interact with neurons by different mechanisms.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.