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Jul 1, 2010 (Vol. 30, No. 13)

Biomagnetic Separations' Abilities Increase

Major Product Expansions Are Surfacing to Support an Assortment of Applications

  • Spheres

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    Thermo Scientific Sera-Mag Magnetic SpeedBeads Carboxylate-Modified exhibit high binding capacity, excellent stability, low nonspecific binding, sensitivity, and slow settling rates, according to the company.

    Ademtech’s latest innovation is a ready-to-use bead for covalent coupling of proteins that has standardized the coupling procedure for immunoassays. Called the Activ-Adembeads, the preactivation step and coupling reagent are built in, according to Sandrine Godichaud, product manager. Monoclonal and polyclonal antibodies, high and low molecular weight proteins, and enzymes have been coupled to these beads, maintaining their activity for downstream applications. “Coupling is fast, flexible, and simple, and leads to a highly reproducible immobilization.” 

    New superparamagnetic microspheres optimized for bioseparation of human cells or bacteria, biopurification of immunoglobulins or recombinant proteins, or biodetection for immunoassays or ELISA are being launched this month at the American Association for Clinical Chemistry conference by Merck Chimie and EMD. The line is introduced “in anticipation of the researcher’s expanding needs for biotools to meet precise assay requirements,” according to Fabrice Sultan, Ph.D., sales and marketing manager, noting that biocoated microsphere requirements for each of those applications differ.

    The new line, called Bio-Estapor®, includes streptavidin, antimouse IgG, antihuman IgG, protein A and protein G coated microspheres, and 0.3 µm, 1.0 µm, and 2.6 µm sizes, with hydrophilic or hydrophobic properties and 30% to 50% ferrite content. The small beads separate slowly but have maximum binding capacity with a higher sensitivity and show “almost no sedimentation during the binding process,” Dr. Sultan says.

    In contrast, “our large coated beads separate fast in a complex or viscous liquid  but will not remain long in solution without agitation or resuspension. The medium size combines efficient magnetophoretic mobility, high surface area, and a low sedimentation rate, making it the gold standard for chemiluminescent immunoassays.”

    “Recently,” Dr. Sultan comments, “protein A and protein G Bio-Estapor microspheres have been used for antibody and Fc-fusion protein purification from cell culture supernatant. The binding activity of the purified proteins was totally preserved, with similar dose responses for proteins purified with protein A sepharose resin. Those coated microspheres have been reused more than 10 times with the same efficacy.”

    Thermo Fisher Scientific recently launched a blocked magnetic particle to control nonspecific binding, according to Rick Galloway, director of particle technology. “Many companies spend a tremendous amount of money adding blockers to their test systems to reduce nonspecific interactions,” he says, increasing assay cost and complicating manufacturing. Instead, Thermo Fisher preblocks the surface of Sera-Mag SpeedBeads before creating an amino-modified surface or the streptavidin-coated version.

    Polysciences’ Bangs Labs division recently introduced the ProMag™ Bind-IT™ and 1 µm ProMag microspheres. According to Kathy Turner, technical service manager, “ProMag Bind-IT are 3 µm polymer-based magnetic microspheres with a preactivated surface that allows ready binding of antibody without sacrificing stability.” The beads and proteins bind during a simple incubation, and Bind-IT’s chemistry immobilizes the antibody while “preserving its tertiary structure for optimal activity.”

    Turner says a new size of ProMag magnetic microspheres is also available. Both the carboxyl and streptavidin versions are now available in a 1 µm size. “The smaller 1 µm size offers far greater surface area per unit weight, which can present a considerable advantage for the purification of biomolecules or capture of low-concentration targets. Smaller-diameter spheres additionally remain suspended for longer periods of time, simplifying assay incubation steps.”

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