An LFA serves as an efficient and portable diagnostic device that utilizes a small liquid sample to detect proteins or the “presence or absence of an analyte.” The device is a small series of pads made from multi-layers of sponge-like, overlapping fabric attached to a dense supporting card for its back. This small unit allows analytes or samples to pass through “capture zones” on a nitrocellulose membrane, with excess liquid traveling to a permeable pad. Color indicator lines allow for a relatively simple, visual interpretation of results.
Source: https://biolanhealth.com/en/lateral-flow-immunoassays