Preparing magnetic beads for a particular assay, such as streptavidin beads, requires the beads to be functionalized. The beads need to be attached to the biological material that will serve as a capture molecule in the application. The particular type of attachment by which a molecule is linked to the bead will depend primarily on two things: the molecule being bound and the aim of the process.
This post is about choosing the right platform for a given biomarker. If you want detailed information about this topic, download our free ebook The Advanced Guide for the use of Magnetic Beads in Chemiluminescent Immunoassays:
The difference between covalent and non-covalent linkages
Bead surface linkages fall into two basic types: covalent and non-covalent. Covalent linkages generally restrict binding to a specific, defined site on the molecule. As such, the manner in which the protein adheres is predictable. The attachment site can be chosen such that the molecule is oriented to maximally expose the desired site to the sample. Covalent binding offers advantages when the capture molecule is small or very expensive, and also when coupling uniformity and stability is key. There are a broad range of covalent linkages available to choose from, yielding some degree of flexibility when it comes to designing the assay.
Surface functional groups that bind via non-covalent attachments include streptavidin, Protein A and Protein G. These groups bind a protein with a lesser degree of stability and with less specificity. Of these, the strongest linkage will be formed by streptavidin, though the attachment will still be weaker than that of a covalent bonding group.
How should I decide between covalent or non-covalent?
The decision to use one type of binding over another should be based on the manner in which you want to present the bound molecule to the sample. If the molecule must be oriented in a very specific way, then a covalent attachment would be the most suitable. For some applications, specificity might not be a concern. In these cases, non-covalent binding groups might be better suited. The driving forces that guide the selection should ultimately be the particular characteristics of the molecule to be bound and the overall aim of the application.
Don't forget to check these posts from our blog in order to get a deeper insight into magnetic beads and immunoassays:
- Using streptavidin magnetic beads in Chemiluminescent Immunoassays
- Moving from Latex Particles to Magnetic Latex Particles
- Finding the Know-How Necessary for In-House Expertise