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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

Calculated capture rates of the device presented by Weddemann et al. [46] in comparison to a straight channel for different lengths (a), cross-section ratios (b), inflow velocities (c), and particle densities (d). If the parameters are not explicitly given, its l = 800 µm, ξ = 1, uin = 200 µm/s and ρpart = 2,500 kg/m3. Reproduced with permission from [46].
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biosensors-03-00327-f004: Calculated capture rates of the device presented by Weddemann et al. [46] in comparison to a straight channel for different lengths (a), cross-section ratios (b), inflow velocities (c), and particle densities (d). If the parameters are not explicitly given, its l = 800 µm, ξ = 1, uin = 200 µm/s and ρpart = 2,500 kg/m3. Reproduced with permission from [46].

Mentions: Furthermore, while this approach circumvents the problems of producing magnetic gradients by conducting lines, as mentioned above, it increases the complexity of the channel system, as a three-dimensional design is required. Additionally, the whole concept of collecting beads only works for slow velocities up to a few hundreds of µm/s, depending on the remaining parameters (see Figure 4(c)). It is possible to adjust the structure to higher velocities by elongating the sensor surface and by increasing the aspect ratio. However, elongating the ramp to counter higher velocities leads to a dilution of beads captured on the surface as the beads spread over a larger area. This decreases the signal strength and, thus, the sensor’s detection threshold. A higher aspect ratio complicates the manufacturing further, leading to increased production costs.


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)

Calculated capture rates of the device presented by Weddemann et al. [46] in comparison to a straight channel for different lengths (a), cross-section ratios (b), inflow velocities (c), and particle densities (d). If the parameters are not explicitly given, its l = 800 µm, ξ = 1, uin = 200 µm/s and ρpart = 2,500 kg/m3. Reproduced with permission from [46].
© Copyright Policy - open-access
Related In: Results  -  Collection

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

biosensors-03-00327-f004: Calculated capture rates of the device presented by Weddemann et al. [46] in comparison to a straight channel for different lengths (a), cross-section ratios (b), inflow velocities (c), and particle densities (d). If the parameters are not explicitly given, its l = 800 µm, ξ = 1, uin = 200 µm/s and ρpart = 2,500 kg/m3. Reproduced with permission from [46].
Mentions: Furthermore, while this approach circumvents the problems of producing magnetic gradients by conducting lines, as mentioned above, it increases the complexity of the channel system, as a three-dimensional design is required. Additionally, the whole concept of collecting beads only works for slow velocities up to a few hundreds of µm/s, depending on the remaining parameters (see Figure 4(c)). It is possible to adjust the structure to higher velocities by elongating the sensor surface and by increasing the aspect ratio. However, elongating the ramp to counter higher velocities leads to a dilution of beads captured on the surface as the beads spread over a larger area. This decreases the signal strength and, thus, the sensor’s detection threshold. A higher aspect ratio complicates the manufacturing further, leading to increased production costs.

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