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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

Schematic drawing of the principle of an on-off ratchet built by Auge et al. [44]. The concentration distribution Con shows the case that all beads have reached the potential minimum of Uon. Coff shows a concentration distribution after an arbitrary diffusion time in the potential Uoff. The fraction of beads that is successfully transported is marked in red. Reproduced with permission from [44].
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biosensors-03-00327-f002: Schematic drawing of the principle of an on-off ratchet built by Auge et al. [44]. The concentration distribution Con shows the case that all beads have reached the potential minimum of Uon. Coff shows a concentration distribution after an arbitrary diffusion time in the potential Uoff. The fraction of beads that is successfully transported is marked in red. Reproduced with permission from [44].

Mentions: However, magnetic fields can be utilized even further. Instead of just assuring contact between bead and sensor surface, they can assist in the transport of beads, rendering microfluidic pumps unnecessary. Lee et al. [43] developed a microelectromagnetic matrix made from two layers of current-carrying wires at 90° angle (see Figure 1(c,d)). By changing the magnetic field patterns created by these structures, they were able to control the movement of a particle cloud of 20 µm diameter with high precision. Another method to achieve transport and even separation of different bead species is the construction of a so-called “magnetic on-off ratchet” [24]. In this concept, a magnetic potential asymmetric in time and space combined with non-directional Brownian motion of magnetic beads leads to a net transport of beads in a specified direction (see Figure 2). When the asymmetric field is switched on, beads move to the potential minima until equilibrium between magnetic forces and Brownian motion is reached, resulting in a narrow concentration distribution (Con). However, if the fields are switched off, the beads begin to diffuse apart, resulting in a broader concentration distribution (Coff) after a few seconds of diffusion. When the fields are reactivated, the beads are once again transported to the minima. Due to the asymmetric shape of the potential, a net transport of beads is achieved.


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)

Schematic drawing of the principle of an on-off ratchet built by Auge et al. [44]. The concentration distribution Con shows the case that all beads have reached the potential minimum of Uon. Coff shows a concentration distribution after an arbitrary diffusion time in the potential Uoff. The fraction of beads that is successfully transported is marked in red. Reproduced with permission from [44].
© Copyright Policy - open-access
Related In: Results  -  Collection

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

biosensors-03-00327-f002: Schematic drawing of the principle of an on-off ratchet built by Auge et al. [44]. The concentration distribution Con shows the case that all beads have reached the potential minimum of Uon. Coff shows a concentration distribution after an arbitrary diffusion time in the potential Uoff. The fraction of beads that is successfully transported is marked in red. Reproduced with permission from [44].
Mentions: However, magnetic fields can be utilized even further. Instead of just assuring contact between bead and sensor surface, they can assist in the transport of beads, rendering microfluidic pumps unnecessary. Lee et al. [43] developed a microelectromagnetic matrix made from two layers of current-carrying wires at 90° angle (see Figure 1(c,d)). By changing the magnetic field patterns created by these structures, they were able to control the movement of a particle cloud of 20 µm diameter with high precision. Another method to achieve transport and even separation of different bead species is the construction of a so-called “magnetic on-off ratchet” [24]. In this concept, a magnetic potential asymmetric in time and space combined with non-directional Brownian motion of magnetic beads leads to a net transport of beads in a specified direction (see Figure 2). When the asymmetric field is switched on, beads move to the potential minima until equilibrium between magnetic forces and Brownian motion is reached, resulting in a narrow concentration distribution (Con). However, if the fields are switched off, the beads begin to diffuse apart, resulting in a broader concentration distribution (Coff) after a few seconds of diffusion. When the fields are reactivated, the beads are once again transported to the minima. Due to the asymmetric shape of the potential, a net transport of beads is achieved.

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