Determination of proteins at nanogram levels by their quenching effect on large particle scattering of colloidal silver chloride

Abstract

A novel quantitative method for the determination of proteins in aqueous solutions has been based on the quenching of the resonance scattering light of colloidal silver chloride in the presence of proteins. The detection limits for eight kinds of proteins (BSA, HSA, egg albumin, human γ-IgG,α-chymotrypsin, E. Coli. alpsase, myoglobin, α-casein) were at about 8 ng/mL; the linear ranges of the calibration curves were 10–400 ng/mL ¶under optimal conditions,except for human γ-IgG (20–¶400 ng/mL), myoglobin (10–300 ng/mL), and α-casein (10–300 ng/mL). Three wavelengths (398 nm, 475 nm, 499 nm) were all suitable for the determination and any acidity from pH 3.0 to pH 9.0 could be chosen. A few non-protein substances at high concentration levels interfered with this method, but this problem could simply be overcome by diluting the samples before the assay. Mechanism studies showed that the quenching effect of proteins on the scattering light of colloidal silver chloride was mainly due to the coagulation of AgCl particles retarded by protein. The method was employed for the determination of total protein in human serum with sactifactory results.