Lateral Flow Immunoassay


The basic LFA strip consists of a linearly arranged sample pad, conjugation pad, nitrocellulose membrane, and a wick. During testing, a sample is added to the proximal end of the strip (the sample pad). Here the sample is processed to make it compatible with the remainder of the test. After treatment, the sample migrates to the conjugate pad where antigens in the sample encounter and interact with immobilized particulate conjugates. The conjugates are typically a colloid gold or latex particle to which either an antigen or antibody has been affixed (depending on the format of the assay). The sample rehydrates the conjugated particles and the analyte in the sample interacts with the conjugate, after which both migrate in complex to the nitrocellulose membrane. As the sample reaches the reaction portion of the nitrocellulose membrane, it encounters a complementary component (either antibody or antigen) with which the conjugated particles can interact only via the presence of the analyte (the presence of which the assay is testing for). A positive result causes a buildup of conjugated particles at the test line, which is interpreted by either a presence or absence of a line, read by either the naked eye.