Bicinchoninic acid (BCA) assay is one of the most common methods of protein determination in biochemical research. The principle of the assay relies on two reactions: first, the reduction of Cu²⁺ to Cu¹⁺ in an alkaline medium by cysteine, cystine, tryptophan, tyrosine, and peptide bonds present in the protein, and second, the chelation of two molecules BCA with one Cu¹⁺ which forms a water-soluble purple-colored complex. The purple-colored product exhibits a strong absorbance at 562 nm that is nearly linear with increasing protein concentrations over a broad working range (6-1,000 µg/mL).

The ZellX^® BCA assay is designed to quantitatively measure protein concentration in a variety of samples. ZellX^® BCA assay Kit, can measure the amount of protein at both low and normal concentration. Cu²⁺ ion is reduced to Cu¹⁺ by protein under alkaline condition which is reacting with bicinchoninic acid to generate a purple‐colored product which is read at 560 nm, proportional to the protein amount. A Bovine Serum Albumin standard is provided to create a standard curve for the assay.