Highly Sensitive Protein Concentration Assay over a Wide Range via Surface-Enhanced Raman Scattering of Coomassie Brilliant Blue

In the Bradford protein assay, protein concentrations are determined by the absorbance at 595 nm due to the binding of Coomassie brilliant blue G-250 (CBBG) to proteins. In a protein-CBBG liquid mixture, surface-enhanced Raman scattering (SERS) is sensitive to the amount of unbound CBBG molecules adsorbed on silver surfaces, and the bound CBBG amount is directly related to the target protein concentration. Accordingly, a novel method for detecting total protein concentration in a solution has been developed based on SERS of unbound CBBG with an internal standard of silicon. Two obvious advantages of the proposed protein assay over conventional Bradford protein assay are its much wider linear concentration range (10(-5)-10(-9) g/mL) and 200 times lower limit of detection (1 ng/mL), which demonstrates its great potential in rapid, highly sensitive concentration determination of high and low-abundance proteins.