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Often in life science research and clinical applications, magnetic carriers are utilized to separate or isolate biomolecules from suspension. In this process, termed biomagnetic separation, biomolecules are coated (or “captured”) onto magnetic beads. Magnetic forces can then be used to pull the coated magnetic beads to a given position in the solution. In order to establish a robust and reproducible standard operating procedure (SOP) for performing biomagnetic separation techniques, one needs to understand how magnetic forces are generated and what key parameters of the experiment need to be controlled.

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This post is about magnetic bead separation and how to validate the process. If you are interested in this topic, download our Free Guide The Starting Guide to Validate Biomagnetic Separation Processes for a helpful guide into defining and optimizing a magnetic bead separation procedure.

Profiling Magnetic Forces

The magnetic force used in any biomagnetic technique depends on the magnetic field profile created by the instrument. For example, in a homogenous magnetic field the magnetic field is equally strong and equally directed (parallel) in all places. Because of this, a homogeneous magnetic field does not generate a force on magnetic objects, though it does generate torque. Hence, if the magnetic field produced by your biomagnetic separator is perfectly homogeneous then your coated magnetic beads will simply rotate in place, and not move in a given direction. As the movement of magnetic beads in the solution is key to the separation process, it is apparent that a different magnetic field pattern is necessary for biomagnetic separation. These magnetic fields, termed inhomogeneous or non-homogeneous magnetic fields, are necessary for generating magnetic force. These principles are key in efficient biomagnetic separation technologies as they are the variations in the magnetic moment and/or magnetic field that cause magnetic beads to move through the solution.

Importantly, the magnetic force used in a separation process is dependent on both the variation of the magnetic field and the magnetic moment of the bead. Superparamagnetic particles have two very different behaviors at lower, versus higher, magnetic fields. At a low magnetic field the magnetic moment of superparamagnetic particles changes linearly, while at a high magnetic field the magnetic moment is nearly constant, at its value saturates: increasing the applied magnetic field no longer increases the magnetic induction.

Generating a Magnetic Force

In magnetic separators, a single permanent magnet is used to generate the necessary magnetic force. Here, the magnetic field strength quickly decreases with distance from the magnet. Additionally, the magnetic field, thus the useful magnetic energy, is not confined in the working volume (the vessel that contains the magnetic bead suspension) . In these configurations, most of the energy is lost to the stray fields.

More modern biomagnetic separation systems, like those provided by Sepmag, generate a constant radial magnetic force with a well-defined strength. The specific magnetic field pattern focuses the  energy created by the magnet on to the working volume, minimizing stray magnetic fields elsewhere. Such modern biomagnetic separation systems are a much more efficient use of magnetic force (faster separation) and, because its strength if spatially constant and well-defined, ensuring the reproducibility of the separation process.

Advanced magnetic bead separation systems show a linear responseIf you found this article interesting and want to gain deeper insight into the use of magnetic forces in magnetic bead separation, make sure to check out these articles from our blog:

 

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Lluis M. Martínez | SEPMAG Chief Scientific Officer

Founder of SEPMAG, Lluis holds a PhD in Magnetic Materials by the UAB. He has conducted research at German and Spanish academic institutions. Having worked in companies in Ireland, USA and Spain, he has more than 20 years of experience applying magnetic materials and sensors to industrial products and processes. He has filed several international patents on the field and co-authored more than 20 scientific papers, most of them on the subject of magnetic particle movement.

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