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.
Highlights
Immuno assays are an established method in medical analysis to determine the concentration of a macromolecular analyte in solution [1,2,3]
Schotter et al [32] have shown that their giant magnetoresistance (GMR) sensor offered a sensitivity superior to fluorescence detection at low analyte concentrations
Their experiment, required a time step of one hour for the beads to bind to the sensor surface
Summary
Immuno assays are an established method in medical analysis to determine the concentration of a macromolecular analyte (antigen) in solution [1,2,3]. Beads, which generally have a low diffusion coefficient due to their comparably large size (primarily, diameters in the range of 100 nm to 10 μm are used for the detection with magneto-resistive sensors), usually settle onto a surface due to gravitational forces only. This requires a long time, depending on the size and density of the particles. Schotter et al [32] have shown that their GMR sensor offered a sensitivity superior to fluorescence detection at low analyte concentrations Their experiment, required a time step of one hour for the beads to bind to the sensor surface. As these approaches have their disadvantages, a new sensor concept that might solve these problems in the future is presented in the final section
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