Polarographic direct determination and homogeneous immunoassay of anti-human serum albumin (HSA) by parallel catalytic hydrogen wave of anti-HSA or HSA

Abstract

Human serum albumin (HSA) or anti-human serum albumin (anti-HSA) yields a catalytic hydrogen wave at about −1.85 V (vs Ag/AgCl) in 0.25 M NH 3·H 2O–NH 4Cl (pH 8.58) buffer. When 1.0×10 −2 M K 2S 2O 8 is present, the catalytic hydrogen wave is further catalyzed, producing a parallel catalytic wave of hydrogen as catalyst in nature, termed the parallel catalytic hydrogen wave. The sensitivity of the parallel catalytic hydrogen wave is higher by two orders of magnitude than that of the catalytic hydrogen wave. Using the parallel catalytic hydrogen wave of anti-HSA or HSA in the presence of K 2S 2O 8, two sensitive methods for the determination of anti-HSA were developed. One is a direct determination based on the parallel catalytic hydrogen wave of anti-HAS itself, and the other is a homogeneous immunoassay based on measuring the decrease of the peak current of the parallel catalytic hydrogen wave of HSA after homogeneous immunoreaction of HSA with anti-HSA. In the direct determination, the second-order derivative peak current of the parallel catalytic hydrogen wave of anti-HSA itself is rectilinear to its titer in the range from 1:1.0×10 7 to 1:8.4×10 6. In the homogeneous immunoassay, the decrease in the second-order derivative peak current of the parallel catalytic hydrogen wave of HSA is linearly related to the added anti-HSA in the titer range from 1:3.0×10 7 to 1:6.0×10 6. These assays are highly sensitive and rapid in operation and can be used to evaluate such antigens and their antibodies as those that could yield the parallel catalytic hydrogen wave.