Immunonanogold Catalytic Resonance Scattering Spectral Assay of Trace Immunoglobulin M

Abstract

Gold nanoparticles of 10 nm were prepared by the improved method of trisodium citrate, and used to label goat anti-human immunoglobulin M (anti-IgM) to obtain a resonance scattering spectral probe for IgM. In pH 4.5 KH₂PO₄-Na₂HPO₄ buffer solution and in the presence of polyethylene glycol, the nanogold-labeled anti-IgM was combined with IgM specifically to form immunogold complex particles. After centrifugation, the immunonanogold in the supernatant catalyzed the reduction of AuCl₄⁻ ions by NH₂OH·HCl to form larger size gold particles in pH 1.9 citrate buffer solution, making the resonance scattering intensity at 580 nm enhanced. The amount of the nanogold-labeled anti-IgM in the supernatant decreased with the addition of IgM. The decreased intensity ΔI_580nm was proportional to the concentration of IgM in the range of 0.06–4.80 ng·mL⁻¹. The regression equation was ΔI_{580 nm}=14.5c(IgM)+1.8, with a detection limit of 0.03 ng·mL⁻¹ IgM. The method was applied to the determination of IgM in sera of healthy humans, with satisfactory results.