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. 2021 Oct 5;12:714242. doi: 10.3389/fmicb.2021.714242

FIGURE 1.

FIGURE 1

Mechanism of action for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) antigen detection through lateral flow assay design. (1) The specimen analyte, containing SARS-CoV-2 antigen suspended in assay buffer, is deposited in the sample well (at 2). (3) The analyte (containing antigen; in green) is absorbed into the sample pad and begins to diffuse across the reaction chamber into the conjugate pad. (4) The analyte comes into proximity of a SARS-CoV-2-specific antigen antibody that is conjugated to a tag (usually consisting of gold, latex, or a fluorophore). (5) The antigen–antibody complex migrates via diffusion across the nitrocellulose membrane. (6) The SARS-CoV-2 antigen–antibody complex comes into proximity of a second SARS-CoV-2 antigen antibody (different epitope) that is covalently bound to the device pad, and an antibody–antigen–antibody complex forms, resulting in the test line. Further diffusion of excess SARS-CoV-2 antibodies (unbound to antigen) results in association of a second covalently bound antibody that is specific for the first SARS-CoV-2 antibody. (7) An antibody–antibody complex forms resulting in the control line.