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Feature Articles : Jul 1, 2006 (Vol. 26, No. 13)

Range of Applications for Biomagnetics

Particle Market Maturing, and Room for Improvement Exists
  • Gail Dutton

This month, Dexter Magnetic Technologies (www.dextermag.com) will ship the first SpeedSep 5000 Bulk Magnetic Separation Station. It also is introducing the LifeSep 5000 SX Magnetic Bead Separator and the LifeSep 1000 SX Magnetic Bead Separator, both for bulk magnetic separations.

These bulk magnetic separators are among a handful of new products that are addressing the bottleneck at the separation step. Other advances in this mature market include new particle coatings and protocols for increasingly specific applications and emerging work to improve the base particles. Work to decrease the particle settling rate is ongoing.

Dexter’s latest innovations are based on its magnet patent (U.S. patent 6,413,420), which produces a high-gradient magnetic field. "The combination of field intensity and high field gradient at the wall creates high particle retention, which allows fluids to be drained off without disturbing the particles that have been separated and attached to the vessel walls," explains Doug Hartl, business manager for medical and LifeSep products. Additionally, because the beads are drawn off the bottom, aspiration is simplified.

Both the SpeedSep and LifeSep product series use strong neodymium-iron-boron magnets to attract and isolate magnetic particles in solution and retain them while the solution is either decanted or aspirated. Both products let users see the sample clearly, which can be particularly important for bead manufacturers wishing to observe bead movement during washing. The SpeedSep and LifeSep each offer a minimal stray field, rapid separation, durability, and ease of use, according to Hartl.

In contrast, Dexter’s SpeedSep 5000 Bulk Magnetic Separation Station is semiautomated, Hartl says. It uses a 5,000-mL vessel for large-scale magnetic particle separation, moving the magnet rather than the vessel. It limits direct access to the magnet for additional safety. It includes a three-way rocker switch to reverse directions and to stop the motor. Options include integrated stirring and/or heating, a cart, and indicator LEDs.

The LifeSept SX series Magnetic Bead Separators are designed for standard 1,000- or 5,000-mL vessels for cell sorting, RNA and DNA isolation, biomolecule purification, and reagent processing. They offer the same basic features as the SpeedSep.

Speeding Things Up

Seradyn(www.seradyn.com) is introducing the SeraMag SpeedBeads, which in a magnetized field, move through solution at twice the speed of Seradyn’s standard beads. Carboxylate- and streptavidin-coated beads have just been released, and an oligo (dt)-coated version is in development.

"For these SpeedBeads, we increased the ratio of magnetite to polymer," explains Rick Galloway, director of particle technology. "There was a very minimal effect on bead size, so the beads are still about 1 micron in diameter." The beads, he says, "offer the best of all worlds, with lots of surface area, high-binding capacity, and a slow settling rate," which is important for clinical diagnostics and molecular biology work.

Seradyn has also improved nonspecific binding properties of its beads. "All beads have some nonspecific binding," Galloway says, but for many applications, such as viral screening, nonspecific binding leads to false positives. By reducing the nonspecific binding, false positives for viral screening have been cut in half, he explains. Putting that in perspective, Galloway says false positives were about two in 10,000 and with Seradyn’s beads, they are about one in 10,000.

Purification System

In late May, Polysciences (www.polysciences.com) introduced the SNARe DNA purification system, based on the BioMag 1-micron superparamagnetic particle. Genomic purification systems are available, including plant genomic purification and plasmid genomic purification.

Chad Owen, vp, particle division, says that the nonspherical SNARe particle has a large surface area that increases the recovery per particle compared to a spherical bead and "looks almost like a corn-flake." Ease of use is a key feature, as no columns or filters are needed, and he says, SNARe is very scaleable.

"We do plan to launch a new base magnetic bead technology in the next few months," Owen says. That polymer-based bead seeks to optimize the balance between surface coating, magnetite loading, and particle settling.

Automation Platform

Sigris (www.sigris.com) is developing complete automation platforms that handle 24 and 36 samples, respectively, for molecular diagnostics. The as-yet-unnamed system is built around Sigris’ MixSep system of magnetic separation, which uses a magnetic field to suspend and mix magnetic particles without agitating the compound. The benefit is mixing without fluid shear, which increases affinity capture, according to founder and CEO Iqbal Siddiqi, Ph.D.

Prototypes of this new system are expected by year’s end. Dr. Siddiqi says the prototypes should lower the price for separating each sample from today’s $6 to $8 to about half that.

Additionally, Sigris’ MCB1200 processing system for biomagnetic purification of nucleic acid now has been validated in the United States and EU and is being marketed in Europe by BioMerieux (www.biomerieux.com) as the MiniMag.

Carboxyl Magnetic Particles

Spherotech (www.spherotech.com) recently added 6- to 8-micron donkey anti-goat IgG-coated polystyrene particles and magnetic particles. An earlier kit offers 4- to 4.5-micron particles. New sizes of carboxyl magnetic particles have been added to its catalog. Particle sizes for its carboxyl magnetic particles now cover the entire range from 0.1 microns to 24 microns.

The company’s true calling, however, is custom work, explains Macarido Hurtado, quality manager. "We have several kinds of beads," including paramagnetic and ferromagnetic beads with high-magnetite content, as well as latex and fluorescent microparticles, allowing greater flexibility for customers with specific needs.

Polymer Labs’ (www.polymerlabs.com) LodeStars disperses microcrystalline ferric oxide uniformly throughout the beads, creating the superparamagnetic properties that cause them to move more rapidly when a magnetic field is applied. That bead is coated in a polymer shell to ensure the iron doesn’t interfere with biological reagents and to provide the chemical groups for covalent attachment of biological molecules.

LodeStars are used in biological samples to manipulate targets, determine which component of a mixture is isolated, and as a solid phase in bioassays to determine which analyte is measured.

Sample Variety

Generally, the time lag in biomagnetic separations is in the actual separation. Roche Applied Science(www.roche-applied-science.com) is working to expand biomagnetic separations’ versatility by evolving the MagNAPure line of separation systems to accommodate a wider variety of sample materials. The most recent introductions are improved RNA isolation kits for its MagNA Pure LC and MagNA Pure Compact Systems.

The MagNAPure LC is a medium- to high-throughput separation system that handles between one and 32 samples in a single isolation run. "It includes protocols, reagents, and consumables for automated isolation of DNA, RNA, mRNA, and total nucleic acids from a variety of sample types, including blood, plasma/serum, tissue, cultures, cells, and bacteria," according to Steve Thomas, product manager, genomics systems instrumentation.

New offerings include the MagNA Pure LC RNA Isolation KitHigh Performance, "for efficient recovery of total RNA from RNase-rich sample types," Thomas notes.

"The MagNAPure LC handles all types of nucleic acid separations," Thomas says, and can perform user-defined post-isolation pipetting for nucleic acid dilution or PCR setup. Once the isolation is complete, the nucleic acid can be eluted to a single 32-well sample container, individual tubes, standard 96-well PCR plates, or into glass capillaries.

The newest system in the MagnaPure family, the MagNAPure Compact, runs up to eight samples simultaneously and has been designed for ease of use while ensuring both quality and quantity of results. This automated system features a UV light for decontamination, sensors to detect specimen clotting, and prefilled reagents and nuclease-free disposables for rapid setup. Liquefied samples are loaded onto the Compact in 2-mL tubes with output eluted into new 2-mL screw-cap tubes. Run time ranges from about 22 to 45 minutes, depending upon the isolation protocol and starting material.

Both the MagnaPure LC and the MagnaPure Compact have windows, allowing researchers to watch the action and visually confirm the status of the separation. Additional shared features include an integrated HEPA, a bar-code scanner, and user-friendly software, Thomas says. To further save time, protocols are already loaded, so there is no need to shut down the system for reagent or protocol changes.

"The biomagnetic particle market is maturing," Owen says, "and is dominated by a few companies." Room for competition remains, however, as does room for improvement.