INFO:
The bicinchoninic acid assay (BCA Assay) is a biochemical assay for determining the total level of protein in a solution, similar to Bradford protein assay. The total protein concentration is exhibited by a color change of the sample solution from green to purple in proportion to protein concentration, which can then be measured using colorimetric techniques.
Protein Quantification (BCA Assay) - DnaTube.com - Scientific Video and Animation Site