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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

A GMR sensor consists of various layers with a soft fm top electrode which acts as a sensing element and can be manipulated by an external magnetic field. When the magnetization vectors of the layers are parallel, electrons with parallel spin alignment pass through the structure almost without scattering. If the layers are magnetized antiparallel, both electron types are scattered strongly. The resistance of the sensor thus changes if beads, or rather their stray field, influence the magnetization of the upper layer.
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biosensors-03-00327-f006: A GMR sensor consists of various layers with a soft fm top electrode which acts as a sensing element and can be manipulated by an external magnetic field. When the magnetization vectors of the layers are parallel, electrons with parallel spin alignment pass through the structure almost without scattering. If the layers are magnetized antiparallel, both electron types are scattered strongly. The resistance of the sensor thus changes if beads, or rather their stray field, influence the magnetization of the upper layer.

Mentions: As mentioned above, beads can be detected via their stray field by magnetoresistive sensors, e.g., GMR sensors. In these sensors, two ferromagnetic (fm) layers are separated by a third, non-magnetic (nm) layer. The giant magnetoresistance effect (GMR effect) was found and originally studied in magnetic multilayer systems [56,57]. Its physical origin has been explained in terms of spin-dependent scattering of conduction electrons at the interface of the magnetic layers [58]. The scattering probability of electrons passing through the structure strongly depends on the relative orientation of the magnetization of the fm layers (see Figure 6). For a parallel orientation of the magnetization vectors of the fm layers the resistance of the device is low, whereas it is high when the magnetizations are aligned antiparallel.


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)

A GMR sensor consists of various layers with a soft fm top electrode which acts as a sensing element and can be manipulated by an external magnetic field. When the magnetization vectors of the layers are parallel, electrons with parallel spin alignment pass through the structure almost without scattering. If the layers are magnetized antiparallel, both electron types are scattered strongly. The resistance of the sensor thus changes if beads, or rather their stray field, influence the magnetization of the upper layer.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

biosensors-03-00327-f006: A GMR sensor consists of various layers with a soft fm top electrode which acts as a sensing element and can be manipulated by an external magnetic field. When the magnetization vectors of the layers are parallel, electrons with parallel spin alignment pass through the structure almost without scattering. If the layers are magnetized antiparallel, both electron types are scattered strongly. The resistance of the sensor thus changes if beads, or rather their stray field, influence the magnetization of the upper layer.
Mentions: As mentioned above, beads can be detected via their stray field by magnetoresistive sensors, e.g., GMR sensors. In these sensors, two ferromagnetic (fm) layers are separated by a third, non-magnetic (nm) layer. The giant magnetoresistance effect (GMR effect) was found and originally studied in magnetic multilayer systems [56,57]. Its physical origin has been explained in terms of spin-dependent scattering of conduction electrons at the interface of the magnetic layers [58]. The scattering probability of electrons passing through the structure strongly depends on the relative orientation of the magnetization of the fm layers (see Figure 6). For a parallel orientation of the magnetization vectors of the fm layers the resistance of the device is low, whereas it is high when the magnetizations are aligned antiparallel.

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