Biomedical subjects

Günter Gauglitz

Publications and source records attributed to Günter Gauglitz.

11 recordsLinked to original sources

PubMed2003

Amidine-based molecularly imprinted polymers-new sensitive elements for chiral chemosensors.

Using the optical measurement technique reflectometric interference spectroscopy (RIfS), the interaction of molecularly imprinted polymers (imprinted with either (R, R)- or (S, S)-2,3-di- O-benzoyltartraric acid) with the corresponding templates and template antipodes were investigated. With these sensors chiral separation with a separation factor of 1.2 could be achieved whereas a reference polymer resulted in no separation. RIfS signals were of opposite sign for imprinted polymer layers containing phenylboronic acid binding site monomers.

Journal Article↗

PubMed2003

Electrosurface phenomena at polymer films for biosensor applications.

Electrosurface phenomena at thin polymer films utilized in the preparation of biosensors have been studied by use of the Microslit Electrokinetic set-up. For the investigated polymer layers (aminodextran, carboxylated dextran, diaminopoly(ethylene glycol), dicarboxypoly(ethylene glycol), biotinylated poly(ethylene glycol), and streptavidin on biotinylated poly(ethylene glycol), the charge formation in aqueous electrolyte solutions was found to depend on the pH value, that is, OH- and H3O+ are the charge determining ions. The isoelectric points obtained from zeta potential versus pH plots could be utilized to draw conclusions on the introduction of acidic or basic groups and on the degree of molecular surface coverage, respectively. The hydrodynamically mobile charge reflected by the magnitude of the zeta potential contributed to only about 6% or less of the total surface conductivity of the polymer layers. The experimental determination of the total surface conductivity was found to provide valuable information on structural features of biosensor interfaces in aqueous environments.

Biosensing Techniques↗

PubMed2003

Urinary nucleosides as potential tumor markers evaluated by learning vector quantization.

Modified nucleosides were recently presented as potential tumor markers for breast cancer. The patterns of the levels of urinary nucleosides are different for tumor bearing individuals and for healthy individuals. Thus, a powerful pattern recognition method is needed. Although backpropagation (BP) neural networks are becoming increasingly common in medical literature for pattern recognition, it has been shown that often-superior methods exist like learning vector quantization (LVQ) and support vector machines (SVM). The aim of this feasibility study is to get an indication of the performance of urinary nucleoside levels evaluated by LVQ in contrast to the evaluation the popular BP and SVM networks. Urine samples were collected from female breast cancer patients and from healthy females. Twelve different ribonucleosides were isolated and quantified by a high performance liquid chromatography (HPLC) procedure. LVQ, SVM and BP networks were trained and the performance was evaluated by the classification of the test sets into the categories "cancer" and "healthy". All methods showed a good classification with a sensitivity ranging from 58.8 to 70.6% at a specificity of 88.4-94.2% for the test patterns. Although the classification performance of all methods is comparable, the LVQ implementations are superior in terms of more qualitative features: the results of LVQ networks are more reproducible, as the initialization is deterministic. The LVQ networks can be trained by unbalanced sizes of the different classes. LVQ networks are fast during training, need only few parameters adjusted for training and can be retrained by patterns of "local individuals". As at least some of these features play an important role in an implementation into a medical decision support system, it is recommended to use LVQ for an extended study.

Adult↗

PubMed2003

New and versatile optical-immunoassay instrumentation for water monitoring.

This article is a review of new and versatile optical-immunoassay instrumentation for water monitoring developed through two European Union projects, RIver ANAlyser (RIANA) and Automated Water Analyser Computer Supported System (AWACSS). Both projects utilise immunoassay techniques to isolate the analytes and Total Internal Reflection Fluorescence (TIRF) to quantify them. Completed in 1999, the RIANA project developed a sensitive and cost-effective analytical system capable of simultaneous detection of multiple-analytes in real-world water samples. The AWACSS project has been in progress since 2001 and is developing rugged-but-sensitive instrumentation that will detect up to 30 analytes simultaneously, will operate unattended, and will have networking capability.

Biosensing Techniques↗

PubMed2002

Discrimination of methanol and ethanol vapors by the use of a single optical sensor with a microporous sensitive layer.

The sorption of methanol and ethanol vapors by a microporous glassy polycarbonate is studied. The increase of the refractive index of the polymer during analyte sorption is measured by surface plasmon resonance. Both analytes are sorbed into the micropores of the polymer showing different diffusion kinetics. The sensor response during analyte exposure is subdivided into different time channels. By evaluating this additional data dimension by neural networks, a simultaneous multicomponent analysis of binary mixtures of ethanol and methanol vapors is possible using the sensor response of only one single sensor. A feature extraction results in an interpretable model and an improved prediction with errors of 2.0% for methanol and 2.4% for ethanol.

Journal Article↗

PubMed2002

Suitability of hyperbranched polyester for sensoric applications--investigation with reflectometric interference spectroscopy.

Hyperbranched polyesters (HBP) with different end groups (P-OH, P-COOH, P-OAc) were prepared as thin films. Their surface properties were investigated using zeta potential and contact angle measurements. The differences in surface properties between P-OH and P-COOH, on the one hand, and P-OAc, on the other hand, predicted different behavior in sensoric applications. Therefore, the vapor of the homologous series of alcohols from methanol to pentanol was exposed to the thin films. Changes in thickness were observed with reflectometric interference spectroscopy (RIfS). First investigations in a current analytical problem for the detection and discrimination of refrigerants (freons) using P-OH as sensitive layer have been shown. Polydimethylsiloxane (PDMS) and poly(ether urethane) (PUT) were used as reference sensor materials for the RIfS measurements.

Journal Article↗

PubMed2002

Use of a modified cyclodextrin host for the enantioselective detection of a halogenated diether as chiral guest via optical and electrical transducers.

In an alkaline rebreathing circuit, the inhalation anesthetic sevoflurane degrades into at least two products, one of them being the chiral halodiether 1,1,1,3,3-pentafluoro-2-(fluoromethoxy)-3-methoxypropane (halodiether B). Using octakis(3-O-butanoyl-2,6-di-O-n-pentyl)-y-cyclodextrin (Lipodex E) as chiral host diluted in the polysiloxane PS255, an exceptional large chiral separation factor alpha of 9.7 at 30 degrees C was found for halodiether B by capillary gas chromatography (cGC). Hence, the interaction of the single enantiomers and the racemic mixture of the halodiether B with Lipodex E was selected as a model system to study the enantioselective recognition by thickness shear mode resonators (TSMR), surface acoustic wave sensors, surface plasmon resonance (SPR), and reflectometric interference spectroscopy. Further investigations of the recognition process by using chemical sensors confirmed the preferential enrichment of the S-enantiomer resulting in 9-fold higher signals. Based on the distinction between enantioselective and nonenantioselective sorption, thermodynamic complexation constants of the single enantiomers with Lipodex E could be determined. The difference in Gibbs free energy -deltaE2,E1(deltaG) of the complexation of the enantiomers of halodiether B with pure Lipodex E was determined at 30 degrees C by TSMR and SPR to be 5.7 or 5.9 kJ/mol, respectively, agreeing well with that determined by cGC, i.e., 5.7 kJ/mol at 30 degrees C.

Journal Article↗

PubMed2002

Label-free parallel screening of combinatorial triazine libraries using reflectometric interference spectroscopy.

The parallel reflectometric interference spectroscopy is presented as a label-free optical detection method. A new setup was adapted to accommodate sample carriers in a 96-well microplate. It allows for the first time simultaneous plate imaging by a CCD camera for the parallel detection of specific biomolecular interaction in the microplate wells at heterogeneous phase using direct optical monitoring. The detection of binding events with time resolution enables a highly parallel functional biomolecular interaction analysis (BIA). The combination of this new screening setup with combinatorial solid-phase synthesis is performed in the wells of glass-bottom microplates to accomplish the synthesis and the screening platform within one device. As a model system for a solid-phase substance library, synthesis of a triazine library and the subsequent BIA with four different antibodies were carried out. The presented setup enables a time resolution of 18 s with a total screening time of less than 35 min including baseline adjustment, BIA, and regeneration of the screening device for 96 samples in parallel. The binding studies reveal a fast classification of the different monoclonal and polyclonal antibodies and enable the detection of triazines with high binding affinity. The presented prototype is the first parallelized optical label-free detection system for biomolecular interaction analysis that is suitable for a high-throughput screening based on the 96-well microplate format.

Antibodies↗

PubMed2002

Online monitoring of solid-phase peptide syntheses on glass-type surfaces using white light interference.

Label-free optical detection methods are of particular value for the investigation of biomolecular interactions. A label-free method based on reflectometric interference spectroscopy is described which enables both the on-line monitoring of solid phase peptide syntheses and subsequently the determination of antibody binding to these peptides without cleavage from the support. The method uses SiO(2) transducers that were modified with diaminopolyethylene glycol. The stepwise coupling of different amino acids to the transducer surface was investigated and the complete monitoring of the synthesis of a viral epitope was performed. The success of the synthesis was proven via binding of a specific monoclonal antibody to the transducer-bound product. In order to demonstrate specificity the binding was inhibited with the same peptide epitope added in solution. The approach is attractive especially in the field of high throughput screening since both the synthesis and the interaction with the biological receptor can be monitored using the same technique.

Amino Acids↗

PubMed2001

Characterisation of antibodies and analytes by surface plasmon resonance for the optimisation of a competitive immunoassay based on energy transfer.

The determination of binding constants using surface plasmon resonance (SPR) was introduced to optimise a competitive homogeneous fluorescence energy-transfer immunoassay (ETIA) before labelling. Steroids were chosen as model for the detection of three analytes estrone, estradiol and ethinylestradiol--by taking three polyclonal antibodies (anti estrone-, anti estradiol- and anti estrogen-antibodies) and the corresponding analyte derivatives used for the immunisation. The active concentration of the antibodies was determined before and after labelling. Inhibition curves were recorded using SPR for all possible combinations of analyte, antibody, and analyte derivatives. The experiments revealed that the active antibody concentration can be reduced to 30% whereas the antibody affinity is not affected by the labelling process. Limits of the use of SPR for determination of affinity constants in solution are discussed. All possible ETIA calibration for the quantification of estrone and estradiol was performed. The lower limits of detection for estrone (0.06 microg L(-1)) and estradiol (0.17 microg L(-1)) were reached with the anti-estrogen IgG and its derivative

Animals↗

PubMed2001

Development of an assay for label-free high-throughput screening of thrombin inhibitors by use of reflectometric interference spectroscopy.

We describe the development of, and analytical conditions used for, parallel affinity assay for thrombin inhibitors adapted to the first label-free optical screening HTS detection set-up fully integrable into a screening platform. To achieve compatibility with pharmaceutical libraries, an HTS-transducer was realized by gluing the bottomless scaffolds of 96- and 384-well plastic microplates on to transducer slides. The transducer are coated with a dextran, to ensure biocompatibility and functionality, and a known thrombin inhibitor was attached covalently to it. By adapting reflectometric interference spectroscopy for simultaneous reading of the whole transducer plate we were able to detect the binding of thrombin in all the wells of the microplates on-line, in parallel, and time resolved. By using an inhibition assay, the screening of 384 substances for thrombin activity can be performed within an assay time of less than 15 min. We also show that the data quality is high enough for parallel quantification of the IC 50 values of the library substances.

Animals↗