Skim milk powder is used as a blocking reagent in immunological assays like Western Blotting or ELISA. It is as well suitable for blocking of nitrocellulose filters in cDNA cloning.It is not suitable for biotin/streptavidin detection systems, because milk contains biotin. Skim milk powder is used as a blocking reagent in immunological assays like Western Blotting or ELISA. It is as well suitable for blocking of nitrocellulose filters in cDNA cloning.It is not suitable for biotin/streptavidin detection systems, because milk contains biotin.