Magnetic beads (in genomics)
Magnetic beads used in genomics are actually superparamagnetic beads. They are made up of tiny (20 to 30 nm) particles of iron oxides, such as magnetite (Fe3O4), which give them superparamagnetic properties.
Superparamagnetic beads are different from more common ferromagnets in that they exhibit magnetic behavior only in the presence of an external magnetic field.
In the presence of appropriate buffers and pH, nucleic acids bind to the different reactive surface of the magnetic bead (e.g. carboxylate modified, Streptavidin, Oligo dT, etc). The magnetic beads are then captured by the application of an external magnet. The solution is then washed to remove unbound molecules and contaminants. Under the right pH, the sample is then eluted from the magnetic beads, allowing for recovery of the nucleic acid from the solution.
Magnetic beads are used for various applications including molecular and immuno assays, and purifying nucleic acids and proteins. They are simple to use, easily scalable, and amenable to automation for increased throughput.