Figure 1. Dexter’s technology integrates magnetic bead separation and resuspension in a single device. Source: Dexter Magnetic TechnologiesFigure 1. Dexter’s technology integrates magnetic bead separation and resuspension in a single device. Source: Dexter Magnetic TechnologiesParticle separation is a common task in the life sciences. In biomedical fields ranging from immunology and proteogenomics to molecular biology and in-vitro diagnostics, it is often necessary or advantageous to isolate bio-molecules like DNA, RNA or proteins from a solution. The separation process is often carried out by using high-gradient magnetic fields to manipulate magnetic beads attached to the target particles.

A typical challenge in the steps leading up to this procedure is ensuring that the concentration of beads is constant and homogenous in the solution. Dexter Magnetic Technologies has solved this issue with a magnetic bead separation and resuspension technology that reliably and repeatably maintains a consistent bead concentration and provides a means to verify both separation and resuspension.

Magnetic bead suspension challenges

Maintaining a uniform and consistent distribution of magnetic beads throughout a solution is critical to successful assays. During storage in a reagent container, beads can settle to the bottom of the bottle, tray or tube, distorting the bead concentration before the solution is pipetted to the microtiter tray to perform an assay. The inaccurate concentration will lead to errors in assay results. In addition, the dense collection of beads at the bottom of the container might be unusable, leading to waste. To avoid these negative outcomes and ensure accurate results, bead concentration must be maintained by periodically resuspending the beads in the solution.

Another common procedure is the purification of bead solutions. This involves several cycles of magnetically forcing the beads to the edge of the container, removing the separated supernatant, adding additional wash solution, and resuspending the beads to achieve consistent concentration and uniform distribution.

The traditional method of bead resuspension, however, is a time-consuming process that consists of transferring the container from the magnetic separator to a mixing apparatus, such as a bottle roller, vortexer or paddle mixer. The container must then be moved back to the magnetic separator to begin the next cycle of purification. Several purification cycles are often necessary before the solution is ready for individual packaging.

Separation and resuspension in a single device

Dexter’s technology accelerates this process by accomplishing both the separation and resuspension of bead solutions with a single device. This eliminates the need to transfer the reagent container back and forth between the magnetic separator and the mixing device, saving valuable time in the overall operation. Furthermore, a tube can be permanently positioned in the container to enable continuous aspiration of the supernatant and dispensing of the wash solution, allowing seamless transitions between process steps without delay.

Operating principle

The device enables continuous separation and resuspension operations by integrating both linear and rotational capabilities. This is an improvement over traditional magnetic separators, which contain only a stationary magnet assembly that projects a motionless magnetic field gradient into the reagent container. Transportation of magnetic beads is caused by the magnetic force generated by the variation of the magnetic field strength with distance across this gradient.

The new device’s motion abilities allow the machine to precisely move and position the magnetic field gradient to achieve not only separation of the magnetic beads, but also resuspension. Rotational motion is accomplished by a rotary solenoid that spins a platform on which the reagent container is placed. Linear motion is produced by a linear slide on which a half-toroidal quadrature magnet assembly is mounted.

Separation of magnetic beads from the solution is achieved by simply holding the assembly stationary. Resuspension of the beads is realized by setting the components into motion. The movement of the magnetic field gradient agitates the magnetic beads in the solution, mixing the solution and resuspending the beads. The rotary solenoid and linear slide are computer controlled, allowing any customized combination of movements for specific separation or resuspension applications. An optical sensor quantitatively verifies bead resuspension and the homogeneity of the solution.

Custom solutions

Dexter Magnetic Technologies provides custom magnetic bead separation and resuspension solutions from desktop-size up to full-size automated systems. Since 1951, the company has been the long-standing resource for leading players in the diagnostics, life sciences and pharmaceutical fields. Today, it is the only magnetic company to offer ISO 13485 products.

For further information, visit Dexter Magnetic Technologies’ website at