Lateral flow immunoassay (LFIA):
The principle behind the LFIA is rather simple: a liquid sample proceeds laterally along the surface of a pad with reactive molecules that bind to the targeted analyte and then migrate along the pad into a detection zone. A liquid sample (or its extract) containing the analyte of interest is applied to the sample pad and moves laterally by capillary flow (without the assistance of external forces) through various zones of polymeric strips, on which are attached molecules that can interact with the analyte. The liquid sample is applied at one end of the strip on the adsorbent sample pad, allowing the sample to migrate through a sample release pad containing antibodies specific to the targeted analyte and are conjugated to colored or fluorescent particles. The sample and the conjugated antibody bound to the targeted analyte then migrate along the strip into the detection zone, which is usually a porous membrane of nitrocellulose containing immobilized detection components such as antibodies or antigens. These components then react with the analyte bound to the conjugated antibody. Typically, the detection zone has a test zone line and a control zone line. The analyte is captured at the test line with the rest of the sample continuing to migrate until reaching the absorbent wicking pad at the other end of the strip. The detection reagent binds at the control line to indicate that the assay has run successfully. The read-out, represented by the lines appearing with different intensities, can be assessed by eye or by using a dedicated reader. LFIA is a fast, low-cost, portable, and easy-to-perform assay with many LFIAs generating a qualitative test result. These characteristics typically make LFIAs ideal for an initial and rapid screening test.
