An immunoassay has been developed for IgA, based on nanogold resonance scattering effect and nanogold labeling. Nanogold in size of 10 nm was prepared by a trisodium citrate method and used to label goat anti-human IgA to obtain an immunoresonance scattering spectral probe for IgA. The immunoreaction between nanogold-labeled antibodies and antigens took place in pH 5.6 Na₂HPO₄-C₆H₈O₇ buffer solution in the presence of PEG 6000 that resulted in the aggregation of the nanogold, and the great linear intensity enhancement of resonance scattering peaks at 580 nm. The assay conditions were considered and optimized. The enhanced intensity ΔI_RS is proportional to the concentrations in the range of 0.0054～1.35 μg•mL^－1 IgA, with a detection limit of 2.0 ng•mL^－1. The method was applied to quantitative determination of IgA in human serum, with satisfactory results.

Key words: immunoglobulin A, nanogold-label, resonance scattering spectral probe