The BCA (Bicinchoninic acid) assay is currently one of the two most commonly used methods for protein concentration measurement in the world. BCA protein quantification consisted of two steps: first, copper divalent ion (Cu²⁺) was reduced to copper monovalent ion (Cu⁺) by the peptide bond of the protein under alkaline conditions; Second, the BCA of both molecules complexate a monovalent copper ion (Cu⁺) to form a purple complex with a strong absorption value at 562 nm, and the absorption value of the complex is linearly related to the concentration of the protein within a certain range (Figure).