There are many variables to consider when designing a magnetic separation system and tailoring it to the experimental goal. Bead surface functionalization is one key component, and often receives the most attention because it is the most obvious point of control for assay specificity. However, it is easy to lose site of the fundamental mechanics of magnetic separation. When designing a magnetic separation protocol it is also important to consider the movement of the magnetic particles in the magnetic field gradient. Superparamagnetic particles will form chains when placed into a magnetic field, a key property to have high enough separation speed for practical purposes.
A combination of immunomagnetic separation separation and PCR have been used to improve the specificity and early detection of Mycobacterium aviumsubsp. paratuberculosis (MAP) DNA in raw cow's milk. An assay for sensitive and early detection of MAP is critical to improving the health of the cows and the dairy industry. A new assay has been developed called IMS-IS1PCR to reflect its two components: immunomagnetic separation (IMS) and IS900 PCR (IS1 PCR). Immunomagnetic separation selectively enriches the population of MAP in milk samples prior to DNA amplification and detection by PCR. The use of magnetic separation is the key component to the success of this new assay. For more information about the magnetic separation process read this article.
Biomagnetic separation is a technique that uses small superparamagnetic iron-oxide particles and a magnet to separate cells or nucleotides from solution. These particles are often called magnetic nanoparticles or microspheres due to their small sizes ranging from less than 100 nm to 5 μm. The magnetic particles are chemically altered (functionalized) to be biologically compatible and to specifically bind to a variety of different cell types. The targets of interest can be bound by the particles and isolated from solution (positive selection) or the unwanted targets can be bound and removed from solution (negative selection). Magnetic bead cell sorting has many advantages over traditional column-based methods due to increased specificity, decreased procedure time, and increased cell viability.
Immunomagentic separation is a selective and faster assay than microbiological culturefor detection of bacteria in food, water, or clinical samples, but it still has limitations. A novel bacteriophage-based magnetic separation has been developed to take the magnetic separation assay to the next level.
When designing a biomagnetic separation strategy it is easy to get caught up in the properties of the superparamagnetic beads and their functional coatings. It is exciting to choose a bead and tailor its surface ligands to perfectly match your target molecule, but don’t stop there! The magnetic separation rack is equally important to a successful identification, isolation, or enrichment protocol. After all, a perfectly designed bead will be useless without a properly designed magnetic rack to recover it from solution.
The study of protein complexes is often difficult due to their physical properties. Proteins are many times hard to isolate with traditional chromatographic methods, especially large molecules in complexes.This is due to most complexes being maintained by non-covalent bonds, which are easily disrupted during isolation.
Magnetic bead technology has developed rapidly in the past decade. New functionalization strategies are continually hitting the market as more laboratories begin to use magnetic separation systems to identify and isolate cells and microorganisms. There is a direct correlation between advanced functionalization strategies and improved assay selectivity. The size of magnetic beads (μm-nm) places them squarely into the cellular realm, and their surface functionalization causes them to bind to specific surface ligands. This functionalization step is crucial to the separation process because it allows the operator to control which cells the beads will bind to. For a positive-selection immunoassay, the bead surfaces are functionalized by covalent attachment of an antibody that will bind to the cell or micro-organism of interest. This bond ensures that the microbe-bead conjugate will be captured in a magnetic field gradient.
