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| Home > Publications database > Magnetic Biosensing and Frequency Mixing Magnetic Detection |
| Conference Presentation (Invited) | FZJ-2023-05288 |
2023
Abstract: For selective detection and quantification of biomolecular targets, we use magnetic label-based immunoassays employing the highly specific interaction between antigens and antibodies bound to magnetic nanoparticle (MNP) markers, which are measured by frequency mixing magnetic detection (FMMD). Superparamagnetic MNP exhibit a nonlinear magnetization. Upon magnetic excitation at two distinct frequencies f1 and f2 incident on the sample, the nonlinearity gives rise to the generation of intermodulation frequencies. Coaxial coils provide magnetic excitation at frequency f1 while the MNP are driven near magnetic saturation with a driving frequency incident on the sample. Response signals generated at linear combination frequencies f1 ± n×f2 are picked up by a detection coil, differentially connected to a reference coil, and are demodulated in the magnetic reader device. The appearance of the mixing components is highly specific to the nonlinearity of the magnetization curve of the particles. The method yields a very large dynamic range of detection, extending to more than 4 orders of magnitude in the number of particles. Analysis of the phase of the response gives information on the magnetic relaxation of the MNP, and thus on their hy-drodynamic size and binding state. Variation of excitation amplitudes or a static magnetic offset field enables determining the size distribution of the magnetic cores of the MNP. With the FMMD technique, magnetic sandwich immunoassays for various biomolecular targets have been successfully realized, exhibiting improved detection limits as compared to conventional techniques like ELISA.
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