Limits...
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) Schematic diagram of a microelectromagnet ring trap developed by Lee et al. [43] to trap magnetic nanoparticles. (b) Micrograph of a fabricated ring trap. (c) Schematic diagram of a microelectromagnet matrix which enables the precise movement of clouds of magnetic particles. The matrix consists of two layers of current-carrying conductors with two layers of insulators. (d) Micrograph of a fabricated matrix (7 × 7 wires). Reproduced with permission from [43].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4263578&req=5

biosensors-03-00327-f001: (a) Schematic diagram of a microelectromagnet ring trap developed by Lee et al. [43] to trap magnetic nanoparticles. (b) Micrograph of a fabricated ring trap. (c) Schematic diagram of a microelectromagnet matrix which enables the precise movement of clouds of magnetic particles. The matrix consists of two layers of current-carrying conductors with two layers of insulators. (d) Micrograph of a fabricated matrix (7 × 7 wires). Reproduced with permission from [43].

Mentions: The trajectory of superparamagnetic beads flowing in microfluidic systems can be controlled with magnetic fields, e.g., produced by on-chip conducting lines [25,26,29,40,41,42,43]. Thus, one possible approach to ensure contact between the antibody-coated beads and the sensor surface is to employ magnetic field gradients that pull the beads towards the sensor. By adjusting the gradient, the force can be limited to altering the trajectory without fixing unbound beads in place above the sensor. After binding is completed, removal of the magnetic field allows for the detection of the stray fields of the beads on the magneto resistive sensor surface. Such trapping schemes were applied by Graham et al. [25] and Lagae et al. [26] for spin-valve sensors. Lee et al. [43] developed a microelecromagnetic ring trap to capture beads in a small volume with a diameter of 60 µm (see Figure 1(a,b)). Li et al. [29] designed a bead concentrator made from current-carrying microstructures that attracts beads and moves them towards a trapping chamber which also serves as the sensing element. This trapping chamber represents a constant volume. When analyte molecules are attached to the beads, their diameter is increased and fewer beads fill the chamber. The underlying TMR sensor then registers the number of beads present in the chamber. This immobilization and detection scheme works best for large biomolecules like DNA. For smaller molecules, additional spacers binding to the analyte are required.


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) Schematic diagram of a microelectromagnet ring trap developed by Lee et al. [43] to trap magnetic nanoparticles. (b) Micrograph of a fabricated ring trap. (c) Schematic diagram of a microelectromagnet matrix which enables the precise movement of clouds of magnetic particles. The matrix consists of two layers of current-carrying conductors with two layers of insulators. (d) Micrograph of a fabricated matrix (7 × 7 wires). Reproduced with permission from [43].
© Copyright Policy - open-access
Related In: Results  -  Collection

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

biosensors-03-00327-f001: (a) Schematic diagram of a microelectromagnet ring trap developed by Lee et al. [43] to trap magnetic nanoparticles. (b) Micrograph of a fabricated ring trap. (c) Schematic diagram of a microelectromagnet matrix which enables the precise movement of clouds of magnetic particles. The matrix consists of two layers of current-carrying conductors with two layers of insulators. (d) Micrograph of a fabricated matrix (7 × 7 wires). Reproduced with permission from [43].
Mentions: The trajectory of superparamagnetic beads flowing in microfluidic systems can be controlled with magnetic fields, e.g., produced by on-chip conducting lines [25,26,29,40,41,42,43]. Thus, one possible approach to ensure contact between the antibody-coated beads and the sensor surface is to employ magnetic field gradients that pull the beads towards the sensor. By adjusting the gradient, the force can be limited to altering the trajectory without fixing unbound beads in place above the sensor. After binding is completed, removal of the magnetic field allows for the detection of the stray fields of the beads on the magneto resistive sensor surface. Such trapping schemes were applied by Graham et al. [25] and Lagae et al. [26] for spin-valve sensors. Lee et al. [43] developed a microelecromagnetic ring trap to capture beads in a small volume with a diameter of 60 µm (see Figure 1(a,b)). Li et al. [29] designed a bead concentrator made from current-carrying microstructures that attracts beads and moves them towards a trapping chamber which also serves as the sensing element. This trapping chamber represents a constant volume. When analyte molecules are attached to the beads, their diameter is increased and fewer beads fill the chamber. The underlying TMR sensor then registers the number of beads present in the chamber. This immobilization and detection scheme works best for large biomolecules like DNA. For smaller molecules, additional spacers binding to the analyte are required.

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