Protein biomarkers remains appealing to drug developers because of the promise of early elimination of ineffective or toxic compounds, improved target validation, and creation of cellular assays for drug discovery. However, the difficulty and costs of characterizing and validating new biomarkers has held back rapid development in this field. Now, new biomagnetic beads are providing ways to identify biomarkers faster, more efficiently, and cheaper.
“For biomarker discovery, investigators can coat beads with the ligand of interest, and either screen samples to identify binders to that ligand, or use coated beads for purifying target.” She adds that in the case of lectin-coated beads, like the company’s soon-to-be-launched BioMag® WGA (wheat germ aglutenin), the lectin binds to its carbohydrate-binding partner. “This is useful for purification of glycoproteins from cell lysate for downstream applications, as well as for certain cell separations that would be more of a biomarker-type application.”
The company offers a suite of various beads. Its BioMag Superparamagnetic particles are used for separation of cells, organelles, proteins, nucleic acids, etc. These irregularly shaped iron-oxide particles contain more than 90% iron oxide for faster magnetic separation. They are covered with a coating that provides functional groups for attachment of proteins or antibodies. BioMag binding proteins include: biotin, Protein A, Protein G, streptavadin, and nuclease-free streptavadin.
“We focus on high coating ability, low, nonspecific binding, and fast pulling speeds so they respond well to the magnet,” states Turner. “It’s up to the customer to choose suitable coatings and optimize them.” Advantages of the beads include a high surface area and an easy format to work with. They also provide great flexibility in that the user can take a population and coat it with different molecules, store it as a wet reagent for significant periods of time, and use it for separation assays.
“A big advantage with microspheres versus a microtiter format is the tremendous surface area you’re presenting to the sample. So there are high capture efficiencies and good binding dynamics.” Also, since most applications involve an automated magnetic separation system, there is a major savings in labor and time, says Turner.
Many customers require magnetic beads with increased speed of response to a magnet, thus Thermo Scientific Seradyn’s (www.seradyn.com) newest member of the Sera-Mag® product line is SpeedBeads, which the company reports is twice as fast as the original particles. These 1-micron carboxylate-modified base particles are made by a core-shell process. “People like the beads to be the same size so they move at the same speed,” explains Rick Galloway, director, particle technology. High-binding capacity is another characteristic customers expect. In order to increase surface area, the beads have a bumpy, cauliflower-like surface.
“All these valleys add greater surface area without changing the diameter. One way others have attempted to increase surface area is to make smaller diameter particles. But the smaller particles respond more slowly to a magnet and that is not good. The way we build our particles is such that the lumpy surface makes them unique, yet they retain the one-micron speed—a nice balance between speed and response,” adds Galloway.
The settling rate in the absence of a magnetic field is yet another important characteristic. SpeedBeads have a slow settling rate—the particles should be floating around and reacting with the target, not dropping to the bottom of the container, explains Galloway.
The most common configurations customers are using for biomarker discovery are SpeedBeads with streptavidin and specific antibodies that have been biotinylated. These feature covalently bound streptavidin with four levels of biotin binding capacity and a shelf life up to five years. The carboxylate-modified beads are the company’s base bead; many customers add their own coating to the surface. “The real optimization lies in tweaking the coating concentration. We’re doing more custom coupling for companies.” The next area of focus for the company will be different surface coatings—more functional, active compounds.