A highly sensitive dual-color lateral flow immunoassay for brucellosis using one-step synthesized latex microspheres

Abstract

A rapid and sensitive lateral flow immunoassay (LFIA) was developed for brucellosis screening. This LFIA used a sandwich format based on the immunological reaction between Brucella lipopolysaccharides (LPSs) and the hosts' anti-LPS IgG antibodies. The latex microspheres were labeled with staphylococcal protein G (SPG) and sprayed onto a conjugation pad. Brucella LPSs were immobilized on the test line of the nitrocellulose membrane. The various IgG antibodies present in serum samples are captured by the latex microsphere (LM)–SPG conjugate to form an LM–SPG–IgG complex; in samples positive for brucellosis, the anti-LPS IgG antibodies present in these complexes then bind to the LPSs on the test line. In this way, the anti-LPS IgG antibodies are enriched during the immunoassay resulting in a positive signal. The carboxyl-functionalized latex microspheres were prepared via emulsifier-free emulsion polymerization synthesis and used for detection. The latex microspheres were spherical and monodisperse with an average diameter of 300 nm. Particles of different colors were obtained by using two different dyes, which enabled dual-color detection on the test strip and whole blood detection without needing a blood filtration pad. The sensitivity of the dual-color LM-LFIA was consistent with that obtained with the Rose Bengal plate test (RBPT) and the reference method, the serum agglutination test (SAT). When tested on actual clinical samples, the sensitivity of the LM-LFIA was very similar to that of colloidal gold-LFIA, but the visual display and signal intensity were improved. These characteristics of the LM-LFIA developed here may prove valuable for the future clinical diagnosis of brucellosis.