PubMed Health⌕ Search

Biomedical subjects

Michael Mayer

Publications and source records attributed to Michael Mayer.

7 recordsLinked to original sources
PubMed2003

Reversible immobilization of peptides: surface modification and in situ detection by attenuated total reflection FTIR spectroscopy.

A generic method is described for the reversible immobilization of polyhistidine-bearing polypeptides and proteins on attenuated total reflecting (ATR) sensor surfaces for the detection of biomolecular interactions by FTIR spectroscopy. Nitrilotriacetic acid (NTA) groups are covalently attached to self-assembled monolayers of either thioalkanes on gold films or mercaptosilanes on silicon dioxide films deposited on germanium internal reflection elements. Complex formation between Ni2+ ions and NTA groups activates the ATR sensor surface for the selective binding of polyhistidine sequences. This approach not only allows a stable and reversible immobilization of histidine-tagged peptides (His-peptides) but also simultaneously allows the direct in situ quantification of surface-adsorbed molecules from their specific FTIR spectral bands. The surface concentrations of both NTA and His-peptide on silanized surfaces were determined to be 1.1 and 0.4 molecules nm-2, respectively, which means that the surface is densely covered. A comparison of experimental FTIR spectra with simulated spectra reveals a surface-enhancement effect of one order of magnitude for the gold surfaces. With the presented sensor surfaces, new ways are opened up to investigate, in situ and with high sensitivity and reproducibility, protein-ligand, protein-protein, protein-DNA interactions, and DNA hybridization by ATR-FTIR spectroscopy.

Adsorption↗
PubMed2003

Monitoring expression and clustering of the ionotropic 5HT3 receptor in plasma membranes of live biological cells.

The ionotropic 5HT(3) receptor was expressed in transiently transfected mammalian cells, yielding an unprecedented high concentration of up to 12 million receptors per cell. Receptor traffic in the plasma membrane of live cells was observed continuously over 24 h by fluorescence scanning confocal microscopy. This was possible by using 5HT(3) receptor-specific fluorescent ligands with high binding affinity and low off-rate to pulse label receptors at any time after appearance on the cell surface, and label subsequently those receptors expressed later by another, spectrally distinguishable, high-affinity fluorescent ligand. Having reached a critical cell surface concentration of approximately 3000 receptors/microm(2), the receptors started to aggregate in patches with a 4-fold increased surface concentration. The clusters were constantly delivered from a pool of freshly expressed receptors isotropically distributed within the basolateral region of the cell membrane. From there, they migrated to and accumulated on the apical cell surface approximately 9 h after transfection. Individual clusters grew until they reached a critical size of 1-2 microm when they merged to form with 3-5 microm large macroclusters. Clustered receptors were immobile on the minute time scale but always coexisted with monomeric receptors in the regions surrounding the clusters as revealed by fluorescence correlation spectroscopy. Because the receptor density of 12 000 receptors/microm(2) in the patches is as high as that found in two-dimensional crystals of certain membrane proteins, such patches might be a proper source for direct crystallization of membrane proteins without prior purification.

Cell Line↗
PubMed2003

Direct estimation of Cole parameters in multifrequency EIT using a regularized Gauss-Newton method.

A major drawback of electrical impedance tomography is the poor quality of the conductivity images, i.e., the low spatial resolution as well as large errors in the reconstructed conductivity values. The main reason is the necessity for regularization of the ill-conditioned inverse problem which results in excessive spatial low-pass filtering. A novel regularization method (SMORR (spectral modelling regularized reconstructor)) is proposed, which is based on the inclusion of spectral a priori information in the form of appropriate tissue models (e.g. Cole models). This approach reduces the ill-posedness of the inverse problem, when multifrequency data are available. An additional advantage is the direct reconstruction of the (physiological) tissue parameters of interest instead of the conductivities. SMORR was compared with posterior fitting of a Cole model to the conductivity spectra obtained with a classical iterative reconstruction scheme at various frequencies. SMORR performed significantly better than the reference method concerning robustness against noise in the data.

Algorithms↗
PubMed2002

Membraneless vanadium redox fuel cell using laminar flow.

This paper describes the design and characterization of a small, membraneless redox fuel cell. The smallest channel dimensions of the cell were 2 mm x 50 mum or x 200 mum; the cell was fabricated in poly(dimethylsiloxane) using soft lithography. This all-vanadium fuel cell took advantage of laminar flow to obviate the need for a membrane to separate the solutions of oxidizing and reducing components.

Carbon↗
PubMed2002

Spine arthroplasty: a historical review.

Degenerative disc disease is one of the most frequently encountered spinal disorders. The intervertebral disc is a complex anatomic and functional structure, which makes the development of an efficient and reliable artificial disc a complex challenge. Not only is the disc function arduous to reproduce, but there are important consequences associated with the conception and the choice of materials that will have to bear the loads. Biochemical problems have complicated things even more. Two different principles have been applied in the realisation of a discal replacement: a metallic and/or polyethylene prosthesis allowing mainly mobility or a prosthesis enabling the reproduction of viscoelastic properties. Of course some devices attempt to combine both principles. In this paper we will try to present, in chronological order, an overview of the designs published in the literature as well as in the patents granted in this field. The very fact that such a long list of implants, based on highly varied principles, has been proposed, and that only very few have reached the level of animal models, let alone human implantation, clearly demonstrates how challenging the task of designing an intervertebral disc replacement is. Proper randomized controlled trials are now on the way, and should help in assessing the efficacy and real place of spine arthroplasty in the treatment of spinal disorders. Only then will spinal surgery join the list of successful joint replacements.

Arthroplasty↗
PubMed2002

Immunoaffinity screening with capillary electrochromatography.

Highly efficient capillary electrochromatographic separations of cardiac glycosides and other steroids are presented. Employing butyl-derivatized silica particles as stationary phase resulted in a nearly three times faster electroosmotic flow (EOF) compared to capillary electrochromatography (CEC) with octadecyl silica particles. On-column focusing with a preconcentration factor of 180 was performed and separation efficiencies of up to 240,000 plates per meter were obtained. Using label-free standard UV absorbance, detection limits of 10-80 nM were reached for all steroids tested. For screening of cardiac glycosides, e.g., digoxin and digitoxin in mixtures of steroids, CEC was combined with immunoaffinity extraction using immobilized polyclonal anti-digoxigenin antibodies and F(ab) fragments. Simply adding small amounts of antibody carrying particles to the samples and comparing chromatograms before and after antibody addition allowed screening for high affinity antigens in mixtures with moderate numbers of compounds. Under conditions of competing antigens, affinity fingerprints of immobilized anti-digoxigenin and anti-digitoxin antibodies were obtained, reflecting the cross-reactivity of eleven steroids. The method provides high selectivity due to the combination of bioaffinity interaction with highly efficient CEC separation and UV detection at several wavelengths in parallel. This selectivity was exploited for the detection of four cardiac glycosides in submicromolar concentrations in an untreated urine sample.

Antibodies↗