BSA blocking buffer in PBS (10X) is 3% bovine serum albumin (BSA), fraction V, immunology grade, in 10X Phosphate buffered saline (PBS, pH: 7.4) with 0.02% sodium azide. BSA blocking buffer in PBS (10X) is used for blocking steps in Western Blot, ELISA, IHC and nucleic acid detection methods. The 3% solution of BSA is useful for saturating excess protein-binding sites on membrane and microplates in immunoassays. BSA blocking buffer in PBS (10X) is usually more effective than nonfat milk blocking buffers for biotin-avidin systems because it contains a single purified protein that is devoid endogenous biotin.The purpose of the blocking step in an assay is to improve assay sensitivity by reducing background interference. Unforeseen cross-reaction of detection reagents with blocking buffers is itself a cause of high background and low signal-to-noise ratios in assay systems. Using inadequate amounts of blocker will result in excessive background. While using excessive blocker concentrations can mask antibody-antigen interactions or inhibit the marker enzyme.