Biomedical subjects

J Spinke

Publications and source records attributed to J Spinke.

8 recordsLinked to original sources

PubMed1998

Translocation of alkali metal cations by lipophilic cyclodextrin derivatives through black lipid membranes.

Lipophilic cyclodextrin (CD) derivatives, synthetic ionophores, were prepared to transport alkali metal cations across a black lipid membrane (BLM). The purpose of this study is to develop a new class of an artificial transportation system of alkali metal cations via bilayer lipid membranes, by using CD derivatives as a cation carrier. A lipophilic CD derivative incorporated into a BLM forms a complex with an alkali metal cation at one surface of the membrane. This charged complex migrates to the opposite side of the membrane and then releases the cation into the subphase. CD derivatives have various types of acyl groups as a complexing site and formed a 1:1 complex with the alkali metal cation. The complex formation was interpreted by an induced-fit mechanism. It is found that the ability of CD derivative for forming a complex and/or transporting cations across the BLM depends on the bulkiness of acyl groups. The conductivities of heptakis (2,6-di-O-propyl-3-O-propionyl)-beta-CD were higher than those of valinomycin regardless of sizes of cations. The order of the conductivity in all derivatives is Li+ < Na+ < K+ approximately = Rb+ approximately = Cs+, regardless of the types of acyl groups in the derivatives. The effects of alkali metal cation concentration in the aqueous phase and CD concentration in the membrane on the translocation are also discussed.

Cations↗

PubMed1997

Sensitivity enhancement of optical immunosensors with nanoparticles.

In recent years, several optical sensor techniques have been developed for the direct monitoring of biomolecular recognition processes at the surface of a sensor chip. Applications of these immunosensors for the determination of substances in serum could be demonstrated only for a few analytes due to the lack of sensitivity. Beside nonspecific binding of serum components to the sensor surface, the analytical sensitivity of these sensors is limited by the molecular weight of the analyte, so that smaller analyte molecules give only a moderate sensor response. In order to enhance the sensor signal, the use of mass labels, such as latex particles, was proposed in the literature. However, detection limits comparable to those of conventional ELISA techniques could not be realized so far. We demonstrate the optimization of a "nanoparticle enhanced immunosensor assay" for the detection of thyroid stimulating hormone, with respect to the particle coating, size, and nonspecific binding. The developed prototype assay requires a sample volume of 225 microL and has a measuring range up to 35 mIU/L. For the first time, we obtained a detection limit of 0.03 mIU/L (0.1 pm), which is fully competitive to conventional ELISA techniques. The assay allows serum samples to be measured with good precision and dilution linearity. The sensor can be reused several times and shows an excellent correlation to a commercial enzyme immunoassay.

Antibodies↗

PubMed1997

Supramolecular architectures for the functionalization of solid surfaces.

Surface plasmon optical techniques are described as sensitive tools that allow for the on-line characterization of supramolecular biofunctional architectures at solid/solution interfaces. After a short introduction into the fundamentals of surface plasmon optics the observation of the build up of a functional bio-interface by the self-assembly process of long chain thiolates at an Au surface is described. Criteria are developed for tailoring the SAM architectures optimized for maximum protein binding from solution by specific bio-recognition reactions. SPM is employed to image the selective binding of streptavidin to a functionalized SAM laterally patterned by UV-photolithographic techniques.

Bacterial Proteins↗

PubMed1994

Electron microscopic investigations on free-standing mixed lipid Langmuir-Blodgett-Kuhn monolayers: phase separation and aging process.

Lipid monolayers were prepared by the Langmuir-Blodgett-Kuhn technique (LBK) as free-standing films spanning a diameter of up to 1 micron. These films were investigated by electron spectroscopic imaging (ESI) and electron energy loss spectroscopy (EELS). The free-standing monolayer is shown to be in a transient state in which an aging process is proceeding: after storage for two weeks in air at room temperature the films tear off the edges of the perforated supporting film. Ca2+ ions induced lateral phase separation in these films prepared from a 50:50 mixture of lecithin/glycerol could be visualized by means of ESI, i.e., by comparing micrographs below and above the Ca absorption edge in the EEL spectrum. The domain sizes of the demixed phases were determined to vary between 30 and 60 nm. In addition it was shown that the counter ion of the negatively charged glycerol in these films is Ca2+ and not Na+.

Calcium↗

PubMed1994

Formation of protein multilayers and their competitive replacement based on self-assembled biotinylated phospholipids.

Based on specific recognition processes the build-up of protein multilayers was achieved using streptavidin layers as a docking matrix. For this purpose, streptavidin was organized at biotin-containing monolayers, liposomes, and self-assembled layers on gold. Thus, mixed double and triple layers of streptavidin, Con A, Fab fragments, and hormones were prepared and characterized by fluorescence microscopy and plasmon spectroscopy. Using biotin analogues with lower binding constants several cycles of multilayer formation followed by competitive replacement could be achieved.

Bacterial Proteins↗

PubMed1993

Attempts to mimic docking processes of the immune system: recognition-induced formation of protein multilayers.

The assemblage of protein multilayers induced by molecular recognition, as seen, for example, in the immune cascade, has been mimicked by using streptavidin as a docking matrix. For these experiments, this protein matrix was organized on liposomes, monolayers at the air-water interface, and self-assembled layers on gold, all three containing biotin lipids. The docking of streptavidin to biotin at liposomal surfaces was confirmed by circular dichroism. Mixed double and triple layers of streptavidin, concanavalin A, antibody Fab fragments, and hormones are prepared at the air-water interface and on gold surfaces and were characterized by fluorescence microscopy and plasmon spectroscopy. With the use of biotin analogs that have lower binding constants it has been possible to achieve multiple formation and competitive replacement of the oriented protein assemblages.

Bacterial Proteins↗

PubMed1992

Streptavidin binding to biotinylated lipid layers on solid supports. A neutron reflection and surface plasmon optical study.

Neutron reflection and surface plasmon optical experiments have been performed to evaluate structural data of the interfacial binding reaction between the protein streptavidin and a solid-supported lipid monolayer partly functionalized by biotin moieties. Since both experimental techniques operate in a total internal reflection geometry at a substrate/solution interface, identical sample architectures allow for a direct comparison between the results obtained with these two recently developed methods. It is found that a monomolecular layer of dipalmitoyllecithin doped with 5 mol% of a biotinylated-phosphatidylethanolamine shows a thickness of d1 approximately (3.4 +/- 0.5) nm. Binding of streptavidin to the biotin groups results in an overall layer thickness of d = (5.9 + 0.5) nm that demonstrates the formation of a well-ordered protein monolayer with the (biotin+spacer) units of the functionalized lipids being fully embedded into the binding pocket of the proteins. It is demonstrated by model calculations that a more detailed picture of the internal structure of this supramolecular assembly can only be obtained if one uses deuterated lipid molecules, thus generating a high contrast between individual layers.

Bacterial Proteins↗

PubMed1991

Lateral order in binary lipid alloys and its coupling to membrane functions.

Densitometry, Raman spectroscopy and small angle neutron scattering are employed to elucidate the miscibility behavior of lipid mixtures organized as liposomal dispersions. First, temperature-composition-phase diagrams for several binary alloys of dialkyl-lecithins differing in chain lengths by an increasing number of CH2-groups are derived. A mixture of dimyristoyllecithin and distearoyllecithin (delta CH2 = 4) shows a peritectic phase behavior with a miscibility gap in the gel state. In the fluid phase, at high enough temperatures, homogeneous mixtures of the two components are formed at all molar ratios. However, upon approaching a critical point by either lowering the temperature or increasing the hydrostatic pressure, critical concentration fluctuations are observed. If one component of a binary mixture is charged, electrostatic interactions can be used to induce phase separation at constant temperature. This is demonstrated for Ca2(+)-driven demixing in alloys of lecithin and negatively charged phosphatidylglycerol. The influence of the various concepts for the induction of lateral structure formation in lipid membranes on integral functional units like ionophores is demonstrated by analysing the single channel current fluctuations of gramicidin in bimolecular lipid membranes. Ca2+, as well as polyelectrolyte-induced phase separations are shown and discussed as examples for the important (lateral) order-function relationship in biomembranes.

Electrochemistry↗