The BCA method is very sensitive for protein detection. Peptide bonds and the four amino acids cysteine, cystine , tryptophan and tyrosine are relevant to the determination. The formation of Cu (I) ions by proteins under alkaline conditions corresponds to the biuret method of determination. A Cu (I ) ion is then bound by two molecules of BCA to a red colour complex. This complex can be detected very sensitively.

BC Assay Kit/Micro BC Assay Kit
Colorimetric method; 562 nm
Compatible with most non ionic and anionic detergents
3 to 4× faster than the classical Lowry method
Linearity: 20 to 2000 µg/ml (BC Assay); 1 to 100 µl/ ml (Micro BC Assay)
Sensitivity: 5 µg/ml (BC Assay Enhanced Protocol)

Coo Assay Protein Determination Kit
Sample size: 1 to 1500 µg/ml
Sensitivity: 1 µg/ml