Determination of trace proteins with pyronine Y and SDS by resonance light scattering

A new resonance light scattering (RLS) probe for determining proteins is presented. The weak RLS of pyronine Y-SDS can be enhanced substantially by adding proteins in the presence of H2SO4, resulting in a strong and wide RLS band in the region 310-425 nm. The interaction of pyronine Y-SDS with proteins was studied on the basis of this behavior and a new quantitative method was developed for determining proteins. The enhanced RLS intensity is proportional to the concentration of proteins in the range 0.15-3.6 microg mL(-1) for bovine serum albumin (BSA) and 0.06-4.8 microg mL(-1) for human serum albumin (HSA), with detection limits of 21.0 and 12.0 ng mL(-1), respectively. This method is characterized by high sensitivity, rapidity of reaction, and simplicity. Four synthetic samples were determined satisfactorily and recovery was 99.5-101.5%. Results for human serum and urine samples were in agreement with those obtained by the Bradford method, with relative standard deviations (RSD) of 1.5-3.1%.