Resonance scattering spectral detection of ultratrace IgG using immunonanogold-HAuCl4-NH2OH catalytic reaction

Nanogold particles of 10 nm were used to label goat anti-human IgG (GIgG) to obtain nanogold-labeled GIgG (AuGIgG). In a citrate-HCl buffer solution of pH 2.27, AuGIgG showed a strong catalytic effect on the reaction between HAuCl4 and NH2OH to form big gold particles that exhibited a resonance scattering (RS) peak at 796 nm. Under the chosen conditions, AuGlgG combined with IgG to form immunocomplex AuGIgG-IgG that can be removed by centrifuging at 16000 r/min. AuGIgG in the centrifuging solution also showed catalytic effect on the reaction. On those grounds, an immunonanogold catalytic RS assay for IgG was designed. With addition of IgG, the amount of AuGlgG in the centrifuging solution decreased; the RS intensity at 796 nm (I(796)nm) decreased linearly. The decreased intensity Delta I(796)nm was linear with respect to the IgG concentration in the range of 0.08-16.0 ng center dot mL(-1) with a detection limit of 0.02 ng center dot mL(-1). This assay was applied to analysis of IgG in sera with satisfactory sensitivity, selectivity and rapidity.