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Biomedical subjects

Joachim O Rädler

Publications and source records attributed to Joachim O Rädler.

9 recordsLinked to original sources
PubMed2006

Decorated rods: a "bottom-up" self-assembly of monomolecular DNA complexes.

Fluorescence correlation spectroscopy (FCS) and gel electrophoresis measurements are performed to investigate both the number and size of complexes of linear double-stranded DNA (dsDNA) fragments with 1:1 diblock copolymers consisting of a cationic moiety, branched polyethyleneimine (bPEI) of 2, 10, or 25 kDa, covalently bound to a neutral shielding moiety, poly(ethylene glycol) (PEG; 20 kDa). By systematically decreasing the bPEI length, the PEG grafting density along the DNA chain can be directly controlled. For 25 and 10 kDa bPEI-PEG copolymers, severe aggregation is observed despite the presence of the shielding PEG. Upon decreasing the bPEI length to 2 kDa, controlled self-assembly of monomolecular DNA nanoparticles is observed. The resulting complexes are in quantitative agreement with a theoretical model based on a single DNA encased in a dense PEG polymer brush layer. The resulting PEGylated complexes show high stability against both salt and protein and hence are of potential use for in vivo gene delivery studies.

DNA↗
PubMed2006

DNA localization and stretching on periodically microstructured lipid membranes.

We study the conformational behavior of DNA molecules adsorbed on cationic-lipid membranes that are supported on grooved, one-dimensionally periodic microstructured surfaces. We reveal a striking ability of these periodically structured membranes to stretch DNA coils. We elucidate this DNA stretching phenomenon in terms of surface curvature dependent potential energy attained by the adsorbed DNA molecules. Because of it, DNA molecules undergo a localization transition causing them to stretch by binding to highly curved sections of the supported membranes.

Adsorption↗
PubMed2006

Structure and mobility of lipid membranes on a thermoplastic substrate.

Supported lipid membranes constitute one of the most important model systems for cell membranes. The properties of lipid membranes supported by the hydrophobic solid polymer cyclic olefin copolymer (COC) were investigated. Lipid layers consisting of varying amounts of 1,2-dioleoyl-3-trimethylammonium propane (DOTAP, cationic) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC, neutral) prepared by vesicle fusion and solvent exchange were compared. All lipid mixtures coated the COC surface homogeneously forming a fluid membrane as verified by fluorescence microscopy and fluorescence recovery after photobleaching (FRAP). The exact structure of the supported membranes was determined by synchrotron reflectivity experiments using a microfluidic chamber. The X-ray data are in agreement with a compressed (head-to-head distance = 29 angstroms) and less densely packed bilayer.

Cations↗
PubMed2006

DNA microelectrophoresis using double focus fluorescence correlation spectroscopy.

Double focus fluorescence correlation spectroscopy (dfFCS) was used to determine electrophoretic mobilities of short double-stranded DNA (dsDNA)-fragments (75 base pairs (bp) -1019 bp) in microfluidic channels. The electrokinetic flow profile across a microchannel was measured with 1 microm spatial resolution and separated in electroosmotic and electrophoretic contributions. Experiments show that the free solution mobility is independent of DNA length. The diffusion constant is additionally determined by FCS and follows a length dependent rod-diffusion model. We interpret the electrophoretic mobilities using a modified Nernst Einstein relation, which additionally takes Manning condensation and counterion induced hydrodynamic retardation forces into account. In 3% w/v polyethylene oxide (PEO)-network (M(r) 3 .10(5) Dalton) the electrophoretic velocities become size-dependent with a power-law exponent be-tween 0.28 and 0.31. Mixtures of dsDNA-fragments exhibit distinguishable peaks in the dfFCS cross-correlation function. The potential of dfFCS for realtime micro-analysis in terms of speed and spatial resolution is discussed.

DNA↗
PubMed2005

Fluorescent nanocrystals as colloidal probes in complex fluids measured by fluorescence correlation spectroscopy.

The diffusion properties of fluorescent colloidal CdSe and CdSe/ZnS nanocrystals (QDs) with different hydrophilic coatings were characterized in complex fluids such as actin solutions using fluorescence correlation spectroscopy (FCS). The hydrodynamic radii of the QDs were determined both in organic solvents and water. Attention was given to the potential artifacts arising from the fluorescence properties of the QDs. With increasing excitation intensities, the apparent particle concentration and diffusion times are overestimated if using a simple diffusion model. This can be explained by a numerical simulation. The diffusion behavior of QDs in actin networks of different concentrations was determined to demonstrate the potential use of nanocrystals as probes in soft biological matter. The decreasing diffusion coefficient of the nanocrystals with increasing actin concentration results in an intrinsic polymer viscosity of 0.12+/-0.02 ml mg(-1), in accordance with literature values.

Actins↗
PubMed2004

Observation of a rectangular columnar phase in a DNA-calcium-zwitterionic lipid complex.

In the presence of calcium, DNA and unilamellar liposomes of the zwitterionic lipid DPPC form a complex in which DNA strands are embedded between a lamellar phase of DPPC. In some complexes, in-plane alignment of the DNA strands occurs, where a DNA-DNA interaxial distance can be measured using small-angle X-ray scattering. Here we report a higher level of DNA organization, with a rectangular columnar phase of DNA identified within this complex structure. This observation is important in view of recent interests in creating new synthetic systems at the interface of biology.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2003

A polyphenylene dendrimer-detergent complex as a highly fluorescent probe for bioassays.

The synthesis of a polyphenylene dendrimer carrying three perylenemonoimide dyes as well as one biotin group is presented. Due to the hydrophobic polyphenylene scaffold, this dendrimer is insoluble in water thus preventing investigations in aqueous media. However, the use of an appropriate detergent results in the formation of well-defined supramolecular dendrimer-detergent complexes being soluble in aqueous media. The dendrimer-detergent complexes have a constant hydrodynamic radius of 7.1 nm measured by light scattering and fluorescence correlation spectroscopy and exhibit a high stability in the presence of blood serum proteins. The specific binding of the dendrimer-detergent complexes carrying a single biotin group to the protein streptavidin is demonstrated using a magnetic bead assay.

Benzene Derivatives↗