A novel protein assay with an azo dye using Rayleigh light scattering technique

The interaction of SPADNS [3-(4-sulfophenylazo)-4,5-dihydroxy-2,7-naphthale ne disulfonic acid] with proteins in acidic solution was studied by spectro photometric and Rayleigh light scattering (RLS) methods. SPADNS reacts rapi dly with albumin at room temperature, and the intensity of the weak RLS of SPADNS was enhanced remarkably and quantitatively by this reaction. Based on this observation, a novel RLS method for serum albumin determinati on was developed. The linear range is 0.125-14.9 mu g/ml for BSA. The relat ive standard deviation (n=10) for 5.0 mu g/ml BSA was 3.94%. The method was applied to the determination of proteins in human plasma and the results w ere compared with the traditional proteins assay (CBB method). There is alm ost no interference from amino acids, metal ions and other coexistent subst ances. The reaction mechanism was also discussed.