Bradford Protein Quantification Assay Kit is based on the direct binding of Coomassie brilliant blue dye to proteins at arginine, tryptophan, tyrosine, histidine, and phenylalanine residues. Specifically, the anionic dye binds to these residues producing an absorbance maximum at 595 nm.
The dye interacts with the protein via van der Waals forces between the hydrophobic regions of the protein and the nonpolar region of the dye and the electrostatic interaction between the negatively charged dye and positively charged amino groups of the protein. The formation of the dye-protein complex takes about two minutes and remains stable for an hour, so the procedure is very fast and the time for trial is not limiting. Additionally, the dye-protein complex has a high extinction coefficient, which makes it a very sensitive assay