Rapid Test Kits

Rapid test kits are a form of immunoassay that do not require specialist equipment or reagents, and have been developed to detect a wide variety of targets. These assays have been adapted to detect both antigens and antibodies, and can be used for a wide variety of applications. Most commercially available rapid test kits are lateral flow assays based on the Colloidal Gold Immunochromatographic Assay (GICA) principle. Many formats of rapid test exist, and the most suitable format depends on the target that is being detected. This page summarizes some of the more common types of Rapid Test Assay.


Antigen Rapid Test Kits (Sandwich)

Antigen present in samples moves along the membrane, and combines with antibodies conjugated to colloidal gold particles. Antibodies specific to the target antigen are fixed to the membrane to form the test line. Antigen that has bound to colloidal gold particles also binds to the fixed antibodies at the test line. When the concentration of antigen in the sample is above a threshold, the colloidal gold conjugates aggregate, leading to a visible colour change forming at the test line. Antibodies specific to the colloidal gold labelled antibody are fixed to the membrane to form the control line. When the colloidal gold labelled antibodies bind to antibodies at the control line, the colloidal gold aggregates to form a colour change. The control line confirms that the concentration of capture antibodies is sufficient for the assay to work normally.


Antigen Rapid Test Kits (Competitive)

Antigen present in samples moves along the membrane. On the conjugate pad, non-sample antigen that has been conjugated to colloidal gold particles mixes with the sample antigen. Antibodies specific to the target antigen are fixed to the membrane to form the test line. The unconjugated sample antigen competes with the conjugated antigen to bind to the fixed antibodies. When the concentration of antigen in the sample is above a threshold, the colloidal gold conjugates do not aggregate, and no colour change is visible at the test line. Antibodies specific to the colloidal gold labelled antibody are fixed to the membrane to form the control line. When the colloidal gold labelled antibodies bind to antibodies at the control line, the colloidal gold aggregates to form a colour change. The control line confirms that the concentration of capture antibodies is sufficient for the assay to work normally.


Antibody Rapid Test Kits

Target antibodies present in samples move along the membrane and bind with anti-IgG or IgM antibodies conjugated to colloidal gold particles. Antigen specific to the target antibody are fixed to the membrane. When the concentration of antibody in the sample specific to the antigen is above a threshold, the colloidal gold conjugates aggregate, leading to a visible colour change forming at the test line. When the colloidal gold labelled antibodies bind to antibodies at the control line, the colloidal gold aggregates to form a colour change. The control line confirms that the concentration of detection antibodies is sufficient for the assay to work normally.