Depending on your target molecule and the specific application, the direct or indirect capture method can be applied using streptavidin magnetic beads (Figure 8).
For some applications, using a pre-coupled ligand in direct capture allows you to reuse the magnetic beads and thus further reduce sample preparation costs.
The indirect capture approach can be of benefit when the concentration of your target is low, the specific affinity is weak, or the binding kinetics is slow. In indirect capture, the probe/ligand is allowed to bind to the target in suspension prior to addition of the beads. A monolayer of streptavidin is covalently coupled to the magnetic beads, helping to reduce leakage that could otherwise disturb your assay.
Figure 8. Direct and indirect capture of molecules and cells with streptavidin magnetic beads. Direct capture uses a pre-coupled ligand that is added to the sample, incubated, then eluted via magnetic separation. Indirect capture begins with incubation of the biotinylated probe/ligand to the sample, then the streptavidin magnetic beads are added and incubated for some time, followed by elution off the magnetic bead by magnetic separation.
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