Magnetize Your Separations

Particles from PerSeptive Biosystems PerSeptive Biosystems' BioMag® product line includes streptavidin-coupled superparamagnetic particles that can be used to capture biotinylated compounds. The company has recently developed a more efficient method for coupling streptavidin to the BioMag® particles. The resultant BioMag® Streptavidin Ultra-Load Particle has more attached streptavidin, and therefore a greater biotin-binding capacity, than did previous versions of the product. The improved particle has been on the market since February of this year, when it replaced the older version. Both the formerly and currently offered streptavidin-conjugated particles are based on BioMag® particles. These particles are approximately 1µm in diameter and differ from some of the other commercially available chromatography beads in that they are irregularly shaped. The surface areas of these non-uniform particles are 20-30 times greater than those of spherical, uniform particles of the same diameter. Harry Glorikian, a product manager at PerSeptive Biosystems, explains that the additional surface area of these particles provides more space that can be used for coupling greater quantities of streptavidin. The difference between the improved BioMag Streptavidin Ultra-Load Particle and the older version of the product is the method used for covalently attaching the streptavidin. The new, proprietary conjugation technique makes better use of BioMag's extra surface area by enabling the conjugation of greater quantities of streptavidin per bead. One milligram of the new BioMag Streptavidin Ultra-Load Particles binds roughly the same amount of biotin as 3-5 mg of the older version of the product. According to PerSeptive Biosystems, 1 mg of streptavidin-coupled Ultra-Load particles will bind at least 1 nmol of biotinylated oligonucleotide, 100 µg of biotinylated IgG, or 2 µg of free biotin. The principles of separation using these particles are simple. Streptavidin-coupled superparamagnetic particles are incubated with the test mixture, allowing biotinylated molecules to bind. A magnetic field is then used to pull the complexes of streptavidin-BioMag particles and biotinylated targets from the suspension, allowing subsequent aspiration of the supernatant. The separation step is fast, generally taking ten minutes or less. BioMag particles are superparamagnetic, enabling them to be used more than once. In other words, although the particles respond well to weak magnetic fields, they do not themselves become permanently magnetized. Thus, they can be repeatedly separated and resuspended without magnetically induced aggregation. The magnetic separators consist of permanent disk or bar magnets encased in plastic. Several different separators are available for varying formats and sample volumes. BioMag® streptavidin-coupled particles can be used for the purification of virtually any class of biotinylated molecule, including proteins, nucleic acids, and lectins. For example, Dr. Shiao Y. Wang, Associate Professor, Department of Biological Sciences, University of Southern Mississippi, used the former version of the streptavidin-coupled particles to isolate single-stranded PCR products for manual DNA sequencing. In this method, one of the PCR primers is tagged with biotin. After PCR amplification, the double-stranded DNA is alkaline-denatured. Then, explains Dr. Wang, the DNA strands containing the biotinylated primer "can be easily and quickly isolated for sequencing" using the streptavidin-conjugated superparamagnetic particles. The improved particles have not been on the market long, but users are switching to them as the need arises. Dr. Hong Jiang, Assistant Professor, College of Physicians and Surgeons, Columbia University, used the new BioMag Streptavidin Ultra-Load Particles in conjunction with a biotinylated antibody to purify a certain subset of T cells. She started with mouse T cells bearing the CD4 surface antigen. Her goal was to remove only those T cells bearing the T-cell receptor (TCR) Vb8, from the CD4-positive population. She first incubated the cells with a biotinylated anti-TCR Vb8 monoclonal antibody. She then used Streptavidin Ultra-Load Particles, at a ratio of about 50 particles/total cell, to deplete the TCR Vb8-positive cells from the other T cells. Dr. Jiang said that this procedure "worked very well," and that she obtained a population of CD4-positive T cells in which 97% of the cells were TCR Vb8-negative. BioMag® Streptavidin Ultra-Load Particles are also suitable for use in a wide variety of other applications, including immunoassays, mRNA quantification, and cell sorting. For more information, visit PerSeptive Biosystems' web site at www.pbio.com, or call (800) 899-5858. The author, Deborah Wilkinson, can be reached at deborahwilkinson@sprynet.com

Magnetize Your Separations

Interested in reading more?

Become a Member of