Determination of proteins at nanogram levels with Bordeaux red based on the enhancement of resonance light scattering

A simple, sensitive and selective method was proposed for the determination of proteins by using a resonance light scattering technique. The weak resonance light scattering (RLS) of Bordeaux red (BR) can be enhanced greatly in the pH range 3.87-3.96 by the addition of micro amounts of proteins, resulting in four characteristic peaks in the wavelength range 250-600 nm. At the maximal wavelength of 363 nm, the enhanced RLS is proportional to the concentration of proteins in the range 0.12-10.8 microg ml-1 for bovine serum albumin (BSA) and 0.24-18.0 microg ml-1 for human serum albumin (HSA). The detection limits were 40.0 and 52.9 ng ml-1 for BSA and HSA, respectively. The present method has been applied to the determination of total proteins in human serum, urine and saliva samples. The obtained results are in good agreement with those obtained by the Bradford method with relative standard deviations (R.S.D.) of 0.9-2.3%.