We have sometimes noticed aggregation with NanoLink™ SA beads, but have recently (Nov 2010) modified our SOP to greatly reduce clumping issues. This can occur from the way the beads are prepared and the SA crosslinked. If you have a sonicator available, you might try performing a 1 minute sonication to disrupt aggregates. After a 30–60 sec sonication treatment, there was very little clumping observed, mostly single beads. Since the beads are very concentrated to begin with (10 mg/mL), the recommendation is that once diluted, that you sonicate your sample for 30–60 sec prior to your application. Beads obtained after November 2010 should experience very little clumping.