Development of immunochromatography for sensitive and rapid detection of Salmonella spp.

Abstract

In this work, the rapid detection of Salmonella typhi (S. typhi) using dot blot immunoassay coupled with optical detection, and immunochromatography was developed. S. typhi was detected using a specific binding reaction between antigens of S. typhi O901 and polyclonal rabbit antibody for polysaccharides of S. typhi O901. Polyclonal rabbit antibody-gold nanoparticles conjugate was used as the label. The detection of S. typhi (mg/mL) was performed by dot blot immunoassay coupled with optical detection. The limit of detection (LOD) was found to be 0.14 mg/mL. Linear region between mean intensity and the concentration of S. typhi was observed with a good coefficient of 0.9986. The detection of S. typhi (cfu/mL) was performed by dot blot immunoassay (direct immunoassay) and immunochromatography (sandwich immunochromatrography). The size of the test strip for sandwich immunochromatography was 0.5 cm in width and 8.3 cm in length. Polyclonal rabbit antibody for polysaccharides of S. typhi O901 and goat anti-rabbit IgG were applied on nitrocellulose membrane to create a test dot and a control dot respectively. Positive results presented two claret-colored dots on nitrocellulose membrane. For negative results, only one control dot appeared on the membrane. The limit of detection was 8.88 × 10⁶ cfu/mL within 1 h and 50 min for dot blot immunoassay, and 1.14 × 10⁵ cfu/mL within 15 min for immunochromatography, which could be visually evaluated by the naked eye. From the result, it could be concluded that immunochromatography provided lower detection limit and reaction time than dot blot immunoassay. In addition, immunochromatography was applied to detect S. typhi in human serum effectively. Therefore, immunochromatography is rapid, simple and low-cost method for the detection of S. typhi.