The problems with magnetic bead suspensions
The major problem with non-colloidal solids suspended in liquids is that they will eventually sediment and clump over time. Magnetic bead suspensions are no exception. Even though magnetic separation is generally gentler than separation by centrifugation, clumps and aggregates can still form. Aggregate formation happens at a much greater frequency if you do not use homogenous biomagnetic separation conditions.
When aggregates form the full reactive surface area on the aggregated beads is not exposed during the subsequent coupling and coating steps. When this happens, the consistency of the lot is compromised. The problem is amplified when large production batches need to be divided into small volumes. If there is a significant amount of aggregation, there will be very little consistency between the aliquots.
This post is about resuspension techniques, such as the sonication method, and how they can solve magnetic bead aggregation. If you are interested in this topic, download our free ebook The basic guide for resuspending magnetic beads:
During the process of coating magnetic beads for use in diagnostic kits, there are several steps in which the solid beads need to be separated from the liquid, washed to remove excess antibodies or other biological coating and then resuspended with new buffers. Every time you separate the beads, you must resuspend them completely or functional consistency of the final bead product will be greatly compromised. This is the key to in-lot consistency. A well-homogenized, non-aggregated suspension will lead to consistent aliquots derived from the larger production volume. Bad resuspension processes lead to high in-lot variability.
Processes of magnetic beads resuspension
The resuspension of magnetic beads is comprised of two different processes:
1. Homogenization of the bead suspension. This entails mixing the suspension such that the bead concentration at any given point in the volume of the liquid is the same. Homogenization is always a necessary technique after each bead/liquid separation step in the production process.
2. Deagglomeration, or disaggregation, of the aggregated magnetic beads. This entails various harsher methods of separating beads that are aggregated, sometimes irreversibly. Sonication is one common method used to help separate aggregated beads. Deagglomeration is only necessary if bead aggregates are formed due to excessive magnetic force during the separation process or if aggregates are formed due to a lack of adequate blocking of the bead surface.
Because of the possible difficulties dealing with aggregated beads, it is vitally important to pay close attention to the proper methods of resuspension. A clear understanding of the key principles of resuspension and how new technologies can alleviate or avoid aggregation will result in more consistent product.
Don't forget to check these posts from our blog in order to get a deeper insight into magnetic bead resuspension:
- The Five Most Used Resuspension Methods: What Works and What Doesn't
- The Two Questions You Must Ask Before Using the Sonication Method with Magnetic Beads
- Three Questions to Help Decide What Technique to Use for Magnetic Bead Mixing and Homogenizing