Includes Abbreviations, Background, and Procedure steps using BSA. The Bradford protein assay (1) is one of several simple methods commonly used to determine the total protein concentration of a sample. The method is based on the proportional binding of the dye Coomassie to proteins. The assay is colorimetric; as the protein concentration increases, the color of the test sample becomes darker. Coomassie absorbs at 595 nm.