The use of magnetic beads for DNA purification and size-selection offers a quick and high yield alternative compared to using column-based cleanups or gel purifications. We have compiled a number of suggestions to improve results for all four parts of magnetic bead based cleanups: adding beads, washing, resuspending and elution.
Adding Beads to Your Sample
- Add the exact volume of beads that is listed in your protocol. Magnetic beads have high DNA binding capacity and adding more beads does not lead to better performance.
- The magnetic bead solution is viscous, so care must be taken to avoid beads sticking to the outside of the pipette tip, which will alter the volume that is transferred to your sample.
- If beads remain on the outside of the pipette tip, drag it against the inside edge of the bead container to remove them before adding the beads to the sample.
- Use low-retention pipette tips when possible.
- After the addition of beads, the solution should be mixed until it is completely homogenous.
- This step is performed with 70 to 80% ethanol. Using ethanol that is too dilute or too concentrated can negatively affect the yield.
- When adding and removing ethanol, be careful to not disturb the bead pellet.
- Make sure that all residual ethanol is removed before proceeding to the next step. To help accomplish this, after the first removal, allow residual ethanol to pool in the bottom of the well and remove this ethanol as well.
- When resuspending in low volumes it may be necessary to pipette the resuspension solution directly on to the bead pellet.
- Over-drying the bead pellet can cause difficulty for resuspension.
- Take care to avoid any bead carryover when transferring the sample.
- When eluting a sample, avoid touching the bead pellet with the pipette tip by resting the tip on the opposite side of the well from the bead.
- Pull up the sample slowly to avoid disturbing the bead pellet
- If using a PCR plate, the used row of the plate can be cut off in order to allow the new well to be in front. When cutting the plate, prevent cross-contamination by sealing the rows containing the samples.
Do you have any questions about magnetic bead based cleanups? If so, email us at BiooNGS@biooscientific.com and we would be happy to help you.