Bio-functionalized magnetic beads are widely used for capturing specific molecules or cells thanks to their super-paramagnetic properties. They are typically used for two main purposes in the Biotech field. They act as the solid phase for both separation processes such as purification of proteins/molecules and for in vitro diagnostics (IVD) reagents.
In order to be able to bind and capture the desired target molecule from the sample, the magnetic beads have to be coated with a ligand that specifically binds the target. The choice of the type of Ligand will entirely depend on the target molecule that has to be captured. The classic and most common ligands are the antibodies, which are used for capturing a broad range of molecules. Nucleic aptamers can also be used in the same way than antibodies. There are a number of alternatives to bind the target molecules, such as Protein A/G, Streptavidin/biotin system, specific proteins or antigens with high specificity and avidity for the target…
The selection of the appropriate type of magnetic particles is key for the success of the project. There are several types of magnetic particles in the market that have different physical and chemical properties. The type of magnetic particles we use will have a big impact on the performance of the binding and the manufacturing and/or reproducibility of different batches of the product. These aspects are also affected by the quality of the magnetic separation process. It is important to work with a separation process that allows in process control and homogeneous separation to assure scalability and reproducibility at big scale.
This article is an excerpt from our newest free guide, Magnetic bead coatings: Today and Tomorrow. If you want to know the most important insights about coating magnetic beads, you can download it through the following link:
From the physical properties point of view, the main parameters to consider for the selection of magnetic particles are the particle size or diameter, the size dispersion of the suspension and their magnetic charge. The particle size will determine the surface area available for coating the ligand and the force by which the particles are attracted by the magnet system during separation. Consequently, the homogeneity of the particle dispersion becomes a critical parameter, as it will have a direct impact on the reproducibility of the performance of different batches of product. The magnetic charge affects the density of the particles and plays a role in the speed of the separation process, which will affect the performance and the manufacturing processes of the product.
The conformation and orientation of the ligand, as well as its density or parking area onto the surface of the particles determines the capacity of the particles to capture the target molecule. The chemical link between the Ligand and the surface of the magnetic particles use to be through covalent binding. There are several commercial magnetic particles available, which are activated with different chemical groups such as carboxylated or amino that allow a covalent binding to the ligand. The most popular ones for chemiluminescence immunoassays are the tosyl-activated particles, which don’t need of pre-activations steps and help to get a reproducible product with low non-specific binding. However, the control of the orientation and conformation is still a challenge for some proteins. There are new technological approaches that help to solve this issue. For instance, metal polymer chemistry can be used to attach proteins to synthetic surfaces via chelation and coordination chemistry as an alternative to the classic covalent binding.
During the next few weeks we will post a series of posts that intends to summarize the current approaches for magnetic bead coating as well as the new arising technological solutions that will help to surpass the current technical challenges.
We’d like to thank the contribution in these posts to some of the best experts worldwide on the present and future of magnetic beads coating.