A rapid, sensitive, and versatile assay for protein using Coomassie brilliant blue G250

An assay for proteins in solution is described that depends on the conversion of Coomassie brilliant blue G250 in dilute acid from a brownish-orange to an intense blue color. As soon as the dye solution is mixed with a protein sample, the absorbance of the mixture can be measured. The absorbance of the solution is stable for 60–90 min at room temperature. The test can be used with a variety of proteins and polypeptides with molecular weights greater than 3000. The assay has high reproducibility and can detect less than 1.0 μg of albumin. The single reagent required is very stable, and free amino acids and several chemicals that interfere with the Lowry protein assay cause no interference. The test is adaptable to a micromethod, which is also described.