Biomedical subjects

R B Schasfoort

Publications and source records attributed to R B Schasfoort.

5 recordsLinked to original sources

PubMed2001

Trends in miniaturized total analysis systems for point-of-care testing in clinical chemistry.

A currently emerging approach enables more widespread monitoring of health parameters in disease prevention and biomarker monitoring. Miniaturisation provides the means for the production of small, fast and easy-to-operate devices for reduced-cost healthcare testing at the point-of-care (POC) or even for household use. A critical overview is given on the present state and requirements of POC testing, on microTAS elements suited for implementation in future microTAS devices for POC testing and microTAS systems for the determination of clinical parameters.

Clinical Chemistry Tests↗

PubMed2001

New approaches for fabrication of microfluidic capillary electrophoresis devices with on-chip conductivity detection.

In practice, microfluidic systems are based on the principles of capillary electrophoresis (CE), for a large part due to the simplicity of electroosmotic pumping. In this contribution, a universal conductivity detector is presented that allows detection of charged species down to the microM level. Additionally, powderblasting is presented as a novel technique for direct etching of microfluidic networks. This method allows creation of features down to 50 microm with a total processing time (design to device) of less than one day. The performance of powderblasted devices with integrated conductivity detection is illustrated by the separation of lithium, sodium, and potassium ions and that of fumaric, malic, and citric acid.

Acids↗

PubMed1995

The ISFET based heparin sensor with a monolayer of protamine as affinity ligand.

The ion-step measuring method was used to determine absolute heparin concentrations in PBS and blood plasma with a Ta2O5 ISFET on to which a monolayer of protamine had been immobilized. Heparin is a highly negatively charged polysaccharide, which is used clinically to delay the clotting of blood. Protamine acts as an affinity ligand for heparin. The response of the ISFET system on a step-wise increase in the electrolyte concentration (a so-called ion-step) is a transient change of the output voltage, which is related to the surface charge density of the ISFET gate oxide. After 2 mins of incubation in a plasma sample containing heparin, the amplitude of the transient ISFET response to an ion-step showed a linear relation to the heparin concentration. In blood plasma, heparin concentrations between 0.3 and 2.0 Units/ml could be determined with an accuracy of +/- 0.08 Units/ml. Heparin concentrations in different plasma samples of heparinized patients were determined and compared with the APTT. No direct relation was found between the APTT and the heparin concentration, but this result was not surprising.

Biosensing Techniques↗

PubMed1993

An immunosensor for syphilis screening based on surface plasmon resonance.

In this paper the development of a surface plasmon resonance (SPR) immunosensor for syphilis screening is described. This immunosensor is based on the detection of antibodies in serum against the causative organism Treponema pallidum. In order to achieve selectivity a recombinant Treponema pallidum membrane protein A (TmpA) was used. This antigen can react with antibodies to T. pallidum, present in serum of syphilitic patients. Reproducible results have been obtained, using a 'sandwich SPR' method: binding of a sandwich antibody to the treponemal antibody after serum incubation was measured in real time while the binding was taking place. The SPR results obtained from ten blind-coded sera corresponded well with classical syphilis tests (Treponema pallidum haemagglutination assay (TPHA), fluorescent treponemal antibody-absorbed test (FTA-ABS), venereal diseases research laboratory flocculation test (VDRL) and TmpA-based enzyme-linked immunosorbent assay (TmpA-ELISA)). Preliminary experiments showed that direct measurement of serum (in the 'one step SPR') is not yet possible, probably as a result of non-uniformity of serum samples. The application of latex beads is considered to solve this problem.

Antibodies, Bacterial↗

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↗