SPRI size selection can be an effective way of enriching for fragments >1.5 kb, and it is routinely performed after DNA extraction. However, this method requires the formulation of a custom solution of SPRI beads before use. Therefore, we investigated the performance of a custom solution of SPRI beads to determine if these beads can be stored.

Lambda DNA was mixed with 1 kb DNA ladder in a 1:1 ratio (mass:mass). A custom solution of SPRI beads was prepared according to the protocol and the SPRI size selection was performed on the Lambda DNA:ladder mix. Sample recovery was recorded and enrichment was assessed using the Agilent Femto Pulse Systems. The solution of SPRI beads was stored at 4°C and the size selection was repeated after 7, 14, 21 and 28 days.

In Figure 1, no decrease in recovery was observed as the age of the buffer increases, we did observe a reduction in the depletion of molecules <1.5 kb (Figure 2). Therefore we advise making up the custom solution of SPRI beads fresh on the day it is required for optimal performance.

Figure 1. The effect of storage of custom SPRI size selection bead solution on the recovery of DNA.

Figure 2. The effect of storage of custom SPRI size selection bead solution on the depletion of DNA molecules <1.5 kb. Note, only data relating to the 500, 1000 and 1500 bp markers is displayed. As the custom solution aged, the depletion of the 1000 and 1500 bp fragments was reduced, compared to the depletion observed at T0.