Biomedical subjects

C Duschl

Publications and source records attributed to C Duschl.

7 recordsLinked to original sources

PubMed2004

Site-directed molecular assembly on templates structured with electron-beam lithography.

We describe a simple method for patterning biomolecular films on surfaces with high resolution. A conventional polymeric resist is structured by electron-beam lithography. The exposed and developed patterns are then used for the directed self-assembly (SA) of a first molecule from solution. Removal of the remaining resist allows the SA of a second species. We illustrate the potential of the approach by assembling on gold (Au) substrates two alkanethiols of contrasting terminal functionality. The patterns have dimensions from the micrometer range down to 40 nm and an edge resolution of 3.5 nm.

Letter↗

PubMed2001

Control of the vibration damping through surface functionalization of a shear force probe.

Shear force mapping on thiolipid Langmuir-Blodgett monolayers probed with Al-coated tips leads to a contrast highly dependent on the monolayer molecular organization, which does not correspond to the topographical relief of the sample. The use of functionalized surface probes offers the possibility to better control the probe-to-sample interaction. In addition, hydrophilic surface probes are totally insensitive to alkyl chain arrangements in the monolayer. Hydrophobic probes, instead, can be chosen to map shear force on soft samples in liquid environment, since their mechanical properties are not influenced by the surrounding liquid.

Microscopy, Fluorescence↗

PubMed2000

Long-range attraction between colloidal spheres at the air-water interface: the consequence of an irregular meniscus

Recent observations of charged colloidal particles trapped at the air-water interface revealed long-range interparticle attractive forces, not accounted for by the standard theories of colloidal interactions. We propose a mechanism for attraction which is based on nonuniform wetting causing an irregular shape of the particle meniscus. The excess water surface area created by these distortions can be minimized when two adjacent particles assume an optimum relative orientation and distance. Typically, for spheres with diameter of 1 &mgr;m at an interparticle distance of 2 &mgr;m, deviations from the ideal contact line by as little as 50 nm result in an interaction energy of the order of 10(4)kT. Roughness-induced capillarity explains the experimental findings, including the cluster dissolution caused by addition of detergent to the subphase and the formation of linear aggregates. This kind of interaction should also be of importance in particle-stabilized foams and emulsions.

Journal Article↗

PubMed1998

A miniaturized monolayer trough with variable surface area in the square-millimeter range.

A new simple concept for a miniaturized monolayer trough is described. The overall monolayer area in the expanded state is approximately 150 mm2 and can be reduced by a factor of 2. The surface area is a function of the shape of the meniscus formed by the subphase and is controlled by the amount of water in the monolayer trough. The controlled compression of monolayers to a desired area per molecule with simultaneous observation of the lateral distribution of fluorescently labeled molecules is shown. A biological reaction between a specific antibody and lipid anchored peptide demonstrates the feasibility of monolayer experiments, which require only very small quantities of substance (in the pmol range). This trough might also be a valuable tool for the 2D crystallization of proteins at lipid layers via specific binding sites such as metal chelators.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1998

Friction anisotropy and asymmetry of a compliant monolayer induced by a small molecular tilt

Lateral force microscopy in the wearless regime was used to study the friction behavior of a lipid monolayer on mica. In the monolayer, condensed domains with long-range orientational order of the lipid molecules were present. The domains revealed unexpectedly strong friction anisotropies and non-negligible friction asymmetries. The angular dependency of these effects correlated well with the tilt direction of the alkyl chains of the monolayer, as determined by electron diffraction and Brewster angle microscopy. The molecular tilt causing these frictional effects was less than 15 degrees, demonstrating that even small molecular tilts can make a major contribution to friction.

Journal Article↗

PubMed1996

Surface engineering: optimization of antigen presentation in self-assembled monolayers.

The formation of self-assembled monolayers (SAMs) on gold surfaces containing an antigenic peptide (NANP)6 and HS(CH2)11OH, and the specific binding of a monoclonal antibody to these layers were investigated by surface plasmon resonance (SPR). Peptides were synthesized by solid-state phase synthesis and were linked either to cysteine or to an alkyl-thiol to allow covalent attachment to gold. The content of the peptide in the SAMs was systematically varied, and the binding properties of the monoclonal antibody were compared with those measured by microcalorimetry in solution. At a critical peptide concentration in the SAM an optimal antibody binding and complete surface coverage was attained. At lower peptide concentrations, the amount of adsorbed antibody decreased; at higher peptide concentrations, the binding constant decreased. These effects can be explained if the accessibility of the antigenic epitopes depends on the peptide density. Addition of free antigen induced the desorption of bound antibodies and allowed accurate measurements of the dissociation rate constant. Binding constants obtained from steady-state measurements and from measurements of the kinetic rate constants were compared.

Amino Acid Sequence↗

PubMed1994

Biologically addressable monolayer structures formed by templates of sulfur-bearing molecules.

We demonstrate that the combined application of Langmuir-Blodgett and self-assembly techniques allows the fabrication of patterns with contrasting surface properties on gold substrates. The process is monitored using fluorescence microscopy and surface plasmon spectroscopy and microscopy. These structures are suitable for the investigation of biochemical processes at surfaces and in ultrathin films. Two examples of such processes are shown. In the first example, the structures are addressed through the binding of a monoclonal antibody to a peptide. This demonstrates the formation of self-assembled monolayers by cysteine-bearing peptides on gold, and the directed binding of proteins to the structured layers. A high contrast between specific and unspecific binding of proteins is observed by the patterned presentation of antigens. Such films possess considerable potential for the design of multichannel sensor devices. In the second example, a structured phospholipid layer is produced by controlled self-assembly from vesicle solution. The structures created--areas of phospholipid bilayer, surrounded by a matrix of phospholipid monolayer--allow formation of a supported bilayer which is robust and strongly bound to the gold support, with small areas of free-standing bilayer which very closely resemble a phospholipid cell membrane.

Amino Acid Sequence↗