The Biuret Assay, also known as the Piotrowski Test, is a biochemical assay that allows one to accurately quantify protein concentration within the range of 5-150 mg/mL. The protein sample, irrespective of its composition, is measured through absorbance spectroscopy at 540 nm in conjunction with a known protein concentration sample.
The Bicinchoninic Acid Assay (BCA), also referred to as the Smiths' Assay, is a biochemical assay designed by Paul Smith in 1985. (Smith, et al., ) This assay uses colorimetric detection and quantification to determine the total concentration of protein in a solution by exhibiting a measurable color change. Applications of this assay include studying protein-protein interactions, estimating percent recovery of membrane proteins from cell extracts, high-throughput screening of fusion proteins, measuring column fractions after affinity chromatography and measuring protein covalently bound to agarose supports and protein adsorbed to multiwell plates.