Biomedical subjects

R P Kooyman

Publications and source records attributed to R P Kooyman.

7 recordsLinked to original sources

PubMed1998

The waveguide Mach-Zender interferometer as atrazine sensor.

Immunoanalytical techniques used in combination with a highly sensitive Mach-Zender waveguide sensor give a device that is capable of fast on-line monitoring of immunoreactions. The on-line monitoring is especially attractive when the sensor can be used as an environmental probe. It is demonstrated that low concentrations of atrazine can be measured with a sensitivity around the EC limit of 100 ng/L. These measurements are performed with an inhibition technique. In combination with "a dynamic slope method" one complete measurement is done within 10 min. Sensor measurements show the same sensitivity and errors as parallel ELISAs.

Atrazine↗

PubMed1997

Heparinization of gas plasma-modified polystyrene surfaces and the interactions of these surfaces with proteins studied with surface plasmon resonance.

Polystyrene surfaces obtained by spin-coating a solution of polystyrene in toluene on a gold layer were functionalized with carboxylic acid groups by preadsorption of the sodium salt of undecylenic acid, followed by an argon plasma treatment. A conjugate of albumin and heparin (alb-hep) was covalently immobilized onto the functionalized surface via preactivation of carboxylic acid groups with a water-soluble carbodiimide. The immobilization of alb-hep conjugate and the subsequent interactions of the heparinized surface with antithrombin III (ATIII, a heparin cofactor) and thrombin were monitored with surface plasmon resonance (SPR). The surface concentration of conjugate as determined with SPR deviated quantitatively from the results obtained with radiolabelled conjugate. The difference in surface concentrations of conjugate obtained with the two methods probably originates from the uncertainty of the refractive index of the alb-hep conjugate in the SPR technique. ATIII could be bound to the surface modified with alb-hep conjugate but not to a polystyrene surface modified with albumin. Rabbit anti-human ATIII did bind to the alb-hep surface previously exposed to ATIII, confirming the presence of surface bound ATIII. The alb-hep immobilized surface was able to bind much more thrombin than ATIII, which is probably due to the less specific heparin-thrombin interaction as compared to the heparin-ATIII interaction. This study shows that SPR is a technique that can be used to study, in real time, both the modification of polymer surfaces and the subsequent interactions of the modified surfaces with proteins.

Albumins↗

PubMed1996

The critical sensor: a new type of evanescent wave immunosensor.

A new planar waveguide immunosensor has been developed in which adsorption at a surface, changing the refractive index contrast, is measured. In this "critical" sensor the change in the effective refractive index contrast is transducted to a shift of the critical reflection angle. The sensor's theoretically. In addition, an experimental sensitivity evaluation on the basis of several immunosensing experiments is presented. The obtained lower detection limit is 2 x 10(-2) nm in adlayer growth, equivalent to 12 pg/mm2 of analyte coverage. This sensitivity is comparable to the performance of the surface plasmon resonance sensors or the grating coupler sensors. However, the "critical" sensor has some advantages. These are mainly the ease of fabrication and adjustment prior to a measurement, and the fact that for an experiment no metal layer has to be used.

Antigen-Antibody Reactions↗

PubMed1994

Immunoreactivity of adsorbed anti human chorionic gonadotropin studied with an optical waveguide interferometric sensor.

A study on the immunoreactivity of adsorbed alpha hCG molecules as a function of substrate hydrophobicity and protein coverage is presented. The experiments were performed with a planar waveguide interferometrical immunosensor. The substrate hydrophobicity and the antibody density were found to be of major importance for the immunoreactivity of the adsorbed antibodies. A combination of a hydrophobic (contact angle > or = 80 degrees) substrate and only a fraction (approximately 0.3) of a monolayer of antibodies gives the highest immunoreactivity. However, the immunoreaction affinity constant of the active antibodies is found to be essentially independent of the substrate hydrophobicity. The experimental results indicate that the orientation and not the conformation of the active antibodies on the substrate is dependent on the substrate hydrophobicity.

Antibodies, Monoclonal↗

PubMed1993

Synthetic peptides as receptors in affinity sensors: a feasibility study.

A relatively simple method for immobilizing synthetic peptides as a receptor onto a gold surface using the self-assembling monolayer (SAM) technique has been investigated. A synthetic peptide with an amino acid sequence similar to the 9-21 gD sequence of herpes simplex virus type 1 was modified with an alkylthiol chain and adsorbed in combination with an alkylthiol chain without peptide according to the SAM procedures. The resulting self-assembled receptor layers (SARs) were able to specifically interact with a monoclonal antibody directed against the 9-21 gD peptide. Binding studies monitored with a surface plasmon resonance setup showed that the response to the antibody depended on the composition of the SAR; a maximum response was reached at approximately 3 mol% peptide coverage. The response itself exceeded the value obtained from passive adsorption of the antibodies under similar conditions, indicating that the formed antibody layer is highly oriented. The equilibrium binding properties of the immobilized receptor molecules were found to be identical to those found when the immobilized antibodies interacted with the receptor molecule. The presence of a hydrophobic moiety in the alkylthiol derivates contributes to the ordering of the monolayer: a less specific interaction occurred when SARs without hydrophobic moiety were used.

Antibodies, Monoclonal↗

PubMed1990

A new approach to immunoFET operation.

A new method is presented for the detection of an immunological reaction taking place in a membrane, which covers the gate area of an ISFET. By stepwise changing the electrolyte concentration of the sample solution, a transient diffusion of ions through the membrane-protein layer occurs, resulting in a transient membrane potential, which is measured by the ISFET. The diffusion rate is determined by the immobile charge density in the amphoteric protein layer, which changes upon formation of antibody-antigen complexes. No membrane potential is induced at zero fixed charge density as occurs at a protein characteristic pH. Isoelectric points of embedded proteins can be determined by detecting the zero potential response. Up to now, the authors have studied the membrane adsorption of lysozyme, human serum albumin (HSA) and the immune reaction of HSA with the antibody anti-human serum albumin (alpha HSA). The influence of protein parameters on the amplitude of the transient can be described with an empirical equation. Assuming Langmuir behaviour, the protein concentration in the solution can well be correlated with the concentration in the membrane. This new detection method is unique concerning direct measurements of charge densities and isoelectric points of amphoteric macromolecules adsorbed in the membrane. The simple procedure of one incubation stage followed by one detection stage, without separate washing and labelling techniques, gives direct information about specific charge properties of the macromolecules to be studied.

Antigen-Antibody Reactions↗

PubMed1983

Angle resolved fluorescence depolarization experiments on oriented lipid membrane systems.

It is demonstrated that angle resolved steady state fluorescence depolarization experiments on oriented lipid membrane systems can be an useful alternative to time-resolved fluorescence depolarization experiments on vesicles. It is shown that some basic assumptions underlying time-resolved experiments are not always valid. The usefulness of the measurement of an additional order parameter, less than P4 greater than is demonstrated.

Chemical Phenomena↗