Fig. 2.

Principle of immunochromatography. This drawing shows lateral flow to detect an antigen. The specimen containing the antigen (Analyte) is placed on the sample pad. The antigen, with the fluid, moves to the conjugate pad where it is bound by a labelled antibody specific to the targeted antigen. The conjugate pad also contains labelled antibodies non-specific to the antigen to be detected. Antigen–antibody complexes migrate through the nitrocellulose membrane and reach the ‘Test line’ area. In this area, antigen-specific antibodies are immobilized to catch the antigen–antibody complexes. When antigen–antibody complexes accumulate in this area, the line becomes visible to the naked eye. The non-specific antibodies also migrate and pass the ‘Test line’ to reach the ‘Control line’ area and that line also becomes visible. The test is considered positive only when the two lines (T and C) are visible. (Reproduced from Paulini et al. [82]).