Microdetermination of proteins by resonance light scattering technique based on aggregation of ferric nanoparticles

A new method for protein determination is presented that allows measurement of proteins at nanogram levels with simple procedure. The method applies a resonance light scattering (RLS) technique, but based on aggregation of ferric nanoparticles on protein template instead of the usual interaction of organic days with proteins. By mixing ferric colloid with sodium cacodylate buffer solution, ferric nanoparticles can be obtained in the size of about 5 nm and kept their positive charges in a wide range of pH 1.8–7.6. The ferric nanoparticles can interact with proteins to form particular aggregates and thus result in strong and stable RLS. Under optimal conditions (wavelength of 451 nm and pH 7.4), few substances interfere with this assay. The detection limitation of bovine serum albumin (BSA) is 6.6 ng/mL and the linear range is 20–700 ng/mL. This method gives almost identical responses for BSA, human serum albumin (HSA) and γ-globulin (γ-G), and can be used for the determination of total proteins in human serum with satisfactory results.