Serum is often used as a blocking agent in immunoassays that utilize an indirect staining/detection strategy where a secondary antibody directly binds an antigen-bound primary antibody. These assays include ELISA, western blot, immunohistochemistry, and immunocytochemistry.
Serum contains a mixture of antibodies, but since it is derived from a non-immunized animal, these antibodies will not bind your intended target antigen. Instead, the IgG in serum blocks sticky sites on tissues or cells to prevent non-specific binding of the labeled IgG antibody.
Ideally, the blocking serum used should be derived from the same species as that in which the secondary antibody was raised. For example, if you are using a goat anti mouse secondary antibody then normal goat serum should be used for blocking. It is not advised that serum from the same host species as the primary antibody be used as this would lead to high background.
Bio-Rad offers sera for a large selection of species, including goat, mouse, rat, or pig. These sera are available with or without preservative. We also offer rabbit complement for use in cytotoxicity studies.
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