The aim is to establish magnetic label-based immunoassays which employ the highly specific interaction between antigenes and antibodies in conjunction with magnetic nanoparticle markers for the detection and quantification of specific biomolecules.
The magnetic frequency mixing method based on the generation of intermodulation products at the nonlinear magnetization curve of the superparamagnetic particles is applied for measuring magnetic beads. Using AC excitation at two different distinct frequencies, a sum frequency component is lock-in detected.
In a typical magnetic immunoassay, suitable antibodies are immobilized in the pores of a polyethylene filter. Then, the sample solution is washed through the filter. Subsequently a solution of biotinylated secondary antibodies and the streptavidin-coated magnetic beads are added. The unbound particles are removed by washing. Only if the sample contains antigens which fit the antibodies, the whole chain of sample, secondary antibody and magnetic bead is captured in the filter. A magnetic measurement allows to quantify the sample by detecting the amount of magnetic beads.
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U.M. Engelmann, A. Shalaby, C. Shasha, K.M. Krishnan, H.-J. Krause, Comparative modeling of frequency mixing measurements of magnetic nanoparticles using micromagnetic simulations and Langevin theory, Nanomaterials 11, 1257 (2021).
S. Achtsnicht, C. Neuendorf, T. Faßbender, G. Nölke, A. Offenhäusser, H.-J. Krause, F. Schröper, Sensitive and rapid detection of Cholera Toxin subunit B using Magnetic Frequency Mixing Detection, PLOS ONE 14, e0219356 (2019).
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