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Lab-on-a-Chip Magneto-Immunoassays: How to Ensure Contact between Superparamagnetic Beads and the Sensor Surface.

Eickenberg B, Meyer J, Helmich L, Kappe D, Auge A, Weddemann A, Wittbracht F, Hütten A - Biosensors (Basel) (2013)

Bottom Line: Different solutions, employing magnetic forces, ultrasonic standing waves, or hydrodynamic effects have been found over the past decades.This concept is based on the granular giant magnetoresistance (GMR) effect that can be found in gels containing magnetic nanoparticles.The proposed design could be realized in the shape of paper-based test strips printed with gel-based GMR sensors.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Thin Films & Physics of Nanostructures, Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany. beickenb@physik.uni-bielefeld.de.

ABSTRACT
Lab-on-a-chip immuno assays utilizing superparamagnetic beads as labels suffer from the fact that the majority of beads pass the sensing area without contacting the sensor surface. Different solutions, employing magnetic forces, ultrasonic standing waves, or hydrodynamic effects have been found over the past decades. The first category uses magnetic forces, created by on-chip conducting lines to attract beads towards the sensor surface. Modifications of the magnetic landscape allow for additional transport and separation of different bead species. The hydrodynamic approach uses changes in the channel geometry to enhance the capture volume. In acoustofluidics, ultrasonic standing waves force µm-sized particles onto a surface through radiation forces. As these approaches have their disadvantages, a new sensor concept that circumvents these problems is suggested. This concept is based on the granular giant magnetoresistance (GMR) effect that can be found in gels containing magnetic nanoparticles. The proposed design could be realized in the shape of paper-based test strips printed with gel-based GMR sensors.

No MeSH data available.


Related in: MedlinePlus

General principle of a gel-based GMR sensor for immuno assays. A droplet of gel containing nanoparticles is deposited on a surface and electrically contacted. Antibodies on the gel surface bind beads that have captured antigens from the solution. The magnetic stray field of the beads influences the resistance of the gel through the granular GMR effect, thus enabling the detection of the concentration of bound beads.
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biosensors-03-00327-f008: General principle of a gel-based GMR sensor for immuno assays. A droplet of gel containing nanoparticles is deposited on a surface and electrically contacted. Antibodies on the gel surface bind beads that have captured antigens from the solution. The magnetic stray field of the beads influences the resistance of the gel through the granular GMR effect, thus enabling the detection of the concentration of bound beads.

Mentions: With the help of these gel-based GMR sensors, a new type of paper-based immunoassay µTAS systems could be developed. Instead of structuring sensors on the bottom of a microfluidic channel, spots of GMR gel could be deposited on a small paper strip, similar to a pH test strip. The gel has to contain functional groups that assemble on the surface of the gel and are able to bind antibodies (see Figure 8). Dipping the strip into a specific antibody solution would then activate the strip for a specific sandwich immunoassay. After mixing the test sample (blood, saliva, etc.) with a bead solution containing the marker beads and antibodies bound on the bead surface, the activated strip could be dipped into the mixture. Antigens in the solution would link antibodies on the bead surface and antibodies on the gel, thus resulting in beads that are bound to the gel surface. Subsequently to a washing step, the strip would be inserted into a standardized magnetic field. The developing stray field of the beads would alter the resistance of the GMR gel, thus allowing the direct measurement of the bead density on the gel surface. As the mixing takes place under macroscopic flow conditions (no laminar flow), the usual problem of contact between beads and surface could be circumvented. However, repulsive double-layer forces would have to be prevented by careful choice of the surface materials. Due to the simplified fabrication of these strips, the production costs of this µTAS system could possibly be low enough to allow for mass production.


Lab-on-a-Chip Magneto-Immunoassays: How to Ensure Contact between Superparamagnetic Beads and the Sensor Surface.

Eickenberg B, Meyer J, Helmich L, Kappe D, Auge A, Weddemann A, Wittbracht F, Hütten A - Biosensors (Basel) (2013)

General principle of a gel-based GMR sensor for immuno assays. A droplet of gel containing nanoparticles is deposited on a surface and electrically contacted. Antibodies on the gel surface bind beads that have captured antigens from the solution. The magnetic stray field of the beads influences the resistance of the gel through the granular GMR effect, thus enabling the detection of the concentration of bound beads.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4263578&req=5

biosensors-03-00327-f008: General principle of a gel-based GMR sensor for immuno assays. A droplet of gel containing nanoparticles is deposited on a surface and electrically contacted. Antibodies on the gel surface bind beads that have captured antigens from the solution. The magnetic stray field of the beads influences the resistance of the gel through the granular GMR effect, thus enabling the detection of the concentration of bound beads.
Mentions: With the help of these gel-based GMR sensors, a new type of paper-based immunoassay µTAS systems could be developed. Instead of structuring sensors on the bottom of a microfluidic channel, spots of GMR gel could be deposited on a small paper strip, similar to a pH test strip. The gel has to contain functional groups that assemble on the surface of the gel and are able to bind antibodies (see Figure 8). Dipping the strip into a specific antibody solution would then activate the strip for a specific sandwich immunoassay. After mixing the test sample (blood, saliva, etc.) with a bead solution containing the marker beads and antibodies bound on the bead surface, the activated strip could be dipped into the mixture. Antigens in the solution would link antibodies on the bead surface and antibodies on the gel, thus resulting in beads that are bound to the gel surface. Subsequently to a washing step, the strip would be inserted into a standardized magnetic field. The developing stray field of the beads would alter the resistance of the GMR gel, thus allowing the direct measurement of the bead density on the gel surface. As the mixing takes place under macroscopic flow conditions (no laminar flow), the usual problem of contact between beads and surface could be circumvented. However, repulsive double-layer forces would have to be prevented by careful choice of the surface materials. Due to the simplified fabrication of these strips, the production costs of this µTAS system could possibly be low enough to allow for mass production.

Bottom Line: Different solutions, employing magnetic forces, ultrasonic standing waves, or hydrodynamic effects have been found over the past decades.This concept is based on the granular giant magnetoresistance (GMR) effect that can be found in gels containing magnetic nanoparticles.The proposed design could be realized in the shape of paper-based test strips printed with gel-based GMR sensors.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Thin Films & Physics of Nanostructures, Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany. beickenb@physik.uni-bielefeld.de.

ABSTRACT
Lab-on-a-chip immuno assays utilizing superparamagnetic beads as labels suffer from the fact that the majority of beads pass the sensing area without contacting the sensor surface. Different solutions, employing magnetic forces, ultrasonic standing waves, or hydrodynamic effects have been found over the past decades. The first category uses magnetic forces, created by on-chip conducting lines to attract beads towards the sensor surface. Modifications of the magnetic landscape allow for additional transport and separation of different bead species. The hydrodynamic approach uses changes in the channel geometry to enhance the capture volume. In acoustofluidics, ultrasonic standing waves force µm-sized particles onto a surface through radiation forces. As these approaches have their disadvantages, a new sensor concept that circumvents these problems is suggested. This concept is based on the granular giant magnetoresistance (GMR) effect that can be found in gels containing magnetic nanoparticles. The proposed design could be realized in the shape of paper-based test strips printed with gel-based GMR sensors.

No MeSH data available.


Related in: MedlinePlus