|MadSci Network: Biochemistry|
Proteins tend to stick to most things non-specifically (plastic, glass, other proteins, lipids, sugars, the surface of a cell, etc.). It it due to their natural charge and hydrophilicity/hydrophobicity. When you work with antibodies, you want to minimize non-specific binding in order to get the best signal to noise ratio you can achieve. In order to do this, a large amount of non-reactive protein such as bovine serum albumin, serum or others is added to the sample in order to coat non-specific protein binding sites with these non-reactive proteins. Serum, BSA, casein or gelatin can also be added to the immunostaining buffers (primary and secondary antibodies, if required) so that non-specific protein binding sites are always coated (association and dissociation is a highly dynamic process).
Now because of the large difference in concentration between BSA and the antibody as well as the inherent specificity of the antibody toward its antigen, only a small amount of antibody normally attaches to non-specific protein binding sites and most of it is instead associated with its antigen, therefore providing a good signal with minimal non-specific binding (i.e., background).
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