Magnetic Particles For Influenza Detection Nanomedicine

Researchers at Massachusetts General Hospital and Harvard Medical School have improved the sensitivity of magnetic relaxation switches (MRSws) to help detect low concentrations of influenza antibodies of either human or animal origin .Until now, magnetic nanoparticles (NPs) that react with targets to form aggregates have been used for MRSws. However, although NP-based MRSws detect highly multivalent viruses or bacteria very well, they are not very sensitive to proteins. The team functionalized iron microparticles and nanoparticles with a peptide (Tag) from a glycoprotein (hemagglutinin) found on the surface of a human influenza virus. They then exposed the two types of particles to antibodies (anti-Tag) to make the magnetic particles aggregate. Measurements of transverse relaxation time, taken using a magnetic relaxometer, were found to give better detection results for microparticles, rather than nanoparticles, simply because they are larger and are detected more easily. This has led the researchers to study three different ways for improving the sensitivity of microparticle assays.

In the first method they decrease the iron microparticle concentration. The anti-Tag antibodies bridge microparticles together to form aggregates.

In the second method they use ‘magnetic-field-enhanced target aggregation’, in which aggregates formed when the magnetic field is applied are stabilized by antibodies once the field is removed.

The third method uses ‘valency-enhanced aggregation,’ which allows anti-Tag antibodies to bind more than two particles at the same time when an additional antibody is added to the mix. Using these methods, the team can improve measurement sensitivity to detect subpicomolar concentrations of antibody.

When a magnetic field (H) is applied, magnetic microparticles labeled with a Tag peptide aggregate. Anti-Tag antibodies stabilize the aggregates when the field is switched off.

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The assay has been developed to be used as point-of-care test for patients or to be used remotely in the field for early detection of avian influenza. The magnetic relaxation devices are small enough to be transported and operated easily in nonclinical environments where outbreaks of bird influenza may pose a public health risk.

Josephson envisions that commercial versions of the assay will be available within two to three years.