Blocker BSA is a 10% (w/v) solution of high-quality BSA that is useful for saturating excess protein-binding sites on membranes and microplates in immunoassays. It is most frequently diluted 10-fold (to 1% BSA) in 1X PBS or 1X TBS for initial testing. Blocker BSA is usually more effective than nonfat milk for biotin-avidin systems because it contains a single purified protein that is devoid of endogenous biotin.