Colorimetric assays are methods to measure protein concentration in samples. They are based on color changes that occur when the protein in the sample interacts with a specific reagent causing color changes that can be measured using a spectrophotometer. Commonly used assays are the Bradford assay, the Lowry assay and the BCA assay.
The Bradford assay is considered a protein concentration measurement experiment based on the binding of the basic amino acids of a protein to a dye present in Bradford reagent (coomassie brilliant blue). This leads to a shift in the absorbance maximum of the dye from 465 to 595
Bradford reagent contains the coomasie blue dye. The cationic (unbound) form is green / red with an absorption maximum at 465 nm. The anionic bound form of the dye, held together by hydrophobic interactions, has an absorption maximum at 595 nm. Thus; the increase of absorbance from 465 to 595 nm is directly proportional to the amount (concentration) of protein bound to the dye.
