A novel immunochromatographic assay using ultramarine blue particles as visible label for quantitative detection of...

Ultramarine blue particles as a novel visible label has been used to develop immunochromatographic assay (ICA). The ultramarine blue particles, as a sodalite mineral with formula: (Na,Ca)₈[(S,Cl,SO₄,OH)₂(Al₆Si₆O₂₄)], can generate a blue visible signal were used as a label for ICA. Ultramarine blue particles were applied to a sandwich immunoassay to detect hepatitis B virus surface antigen (HBsAg). Ultramarine blue particles were separated from ultramarine blue industrial product by centrifugation. The polyacrylic acid (PAA) was used to modify the carboxyl group on the surface of ultramarine blue particles. The goat anti-HBsAg monoclonal antibody was modified on ultramarine blue particles by EDC/NHS activation of the carboxyl groups. In the presence of HBsAg, the immune ultramarine blue particles were bound on test line zone and forming a blue line on ICA strip which was directly readout by naked eye and quantitatively measured by Image J software. Under optimal conditions, the color depth of test line was linearly correlated with the concentration of HBsAg in concentration range from 1 to 50 ng mL^-1. The calibration equation was y = 385.796 + 97.2298x (R² = 0.9872), with limit of detection (LOD) of 0.37 ng mL ^-1(S/N = 3). The sensitivity of this novel ICA was better than that of ICA based on traditional gold nanoparticles as reporter probe. The ultramarine blue particles offer an alternative type of visible label nanomaterial for the development of ICA.