ImmunoMagnetic Reduction (IMR) Assay

Mechanism
ImmunoMagnetic Reduction (IMR) reagents contain homogeneously dispersed magnetic nanoparticles coated with a type of hydrophilic surfactants where bio-probes such as antibodies are conjugated onto. Under external multiple ac magnetic fields, magnetic nanoparticles oscillate with the multiple ac magnetic fields via magnetic interaction. Thus, the reagent under external multiple ac magnetic fields shows a magnetic property, called mixed-frequency ac magnetic susceptibility Xac. Via the binding activity of bio-probes on the outmost shell of magnetic nanoparticles, target bio-molecules (e.g. antigens) can be detected by measuring the reduction in the magnetic signal due to larger sizes of the resulting magnetic nanoparticles.

This is why the method is referred as ImmunoMagnetic Reduction. In principle, when more target molecules are present with the reagent, more magnetic nanoparticles become larger. A larger reduction in Xac could be observed.

Merits
IMR exhibits several unique merits, as described below.

Samples and reagents are always in the same tubes. There is no wash step during the assay.
Only one bio-probe (antibody) against one epitope is used. Truncated target fragments can be also detected as long as fragments with the epitope are present in the sample.
Magnetic nanoparticles show high surface-to-volume ratio. The binding area between antibodies and target molecules in an assay is extremely large, which results in a high sensitivity.
The non-specific binding between bio-probes and bio-molecules in samples is mostly suppressed due to fast oscillation of magnetic nanoparticles during assay that creates a strong centrifugal force enough to break the binding of non-specific molecules but but not the targets.

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