Separation technology is one of the most complex and important areas of biotechnology. Cost-effective separation techniques are a crucial factor in industrial biotechnology production or molecular biological routine diagnostic procedures.
Biomagnetic separation techniques are becoming increasingly important with a wide range of possible applications in the biosciences. Magnetic micro- or nanospheres can be separated easily and quickly by magnetic forces and will be used together with bioaffine ligands, e.g. antibodies or proteins with a high affinity to the target.
The principle behind biomagnetic separation is the action of a magnetic force on particles in a solution. Even a simple block magnet will exert some degree of force onto a nearby test-tube. The process of refining this set-up with improved orientation of the magnets and fluid to be separated has precipitated the high-quality biomagnetic separation products we use today.
The special advantages of magnetic separation techniques are the fast and simple handling of a sample vial and the opportunity to deal with large sample volumes without the need for time-consuming centrifugation steps.
This also makes biomagnetic separation ideal for automated assay / analysis systems which will play a very important role in the near future.
Magnetic particles for bioseparation consist of one or more magnetic cores with a coating matrix of polymers, silica or hydroxylapatite with terminal functionalized groups.
The magnetic core generally consists either of magnetite (Fe3O4) or maghemite (gamma Fe2O3) with superparamagnetic or ferromagnetic properties.
Superparamagnetism is when the dipole moment of a single-domain particle fluctuates rapidly in the core due to the thermal excitation so that there is no magnetic moment for macroscopic time scales. Thus, these particles are non-magnetic when an external magnetic field is applied but do develop a mean magnetic moment in an external magnetic field.
In contrast, ferromagnetism means that the particles have a permanent mean magnetic moment. Here, the larger effective magnetic anisotropy suppresses the thermally activated motion of the core-moments.
Advantages of the superparamagnetic particles are easy resuspension, large surface area, slow sedimentation and uniform distribution of the particles in the suspension media.
Once magnetized, the particles behave like small permanent magnets, so that they form aggregates or lattice due to magnetic interaction.
Advantages of ferromagnetic particles are very strong magnetic properties and therefore the fast separation with an external magnetic field even in viscous media.