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mmunochromatography assay

Immunochromatography assay (ICA), namely lateral flow test, is a simple device intended to detect the presence or absence of the target analyte. The concept of immune chromatography is a combination of chromatography (separation of components of a sample based on differences in their movement through a sorbent) and immunochemical reactions. The most widespread immunochromatographic system is the test strip. Strips used for ICA contain four main components: Sample Application Pad, Conjugate Pad, Substrate (Nitrocellulose) Membrane and Absorbent Pad. Lateral flow assay combines several variants such as formats, biorecognition molecules, labels, detection systems and applications. One of the assay formats is the same as the sandwich ELISA method. The only difference is that immunological reaction is carried out on the chromatographic paper by capillary action. For this system, two kinds of specific antibodies against the antigen are used. One of the antibodies is immobilized on the chromatographic paper while another is labeled with colloidal gold and infiltrated into a sample pad. An immunochromatographic unit is completed by attaching the sample pad at the end of the membrane. The liquid sample is dropped on the sample pad. The antigen in the sample forms an immunocomplex with the antibody labeled with colloidal gold. Its complex moves along with the liquid sample and makes a contact with the antibody immobilized on the membrane. It is followed by forming an immune-complex with the immobilized antibody. It results in generating a coloured red-purple line. The appearance of a red-purple line on the membrane indicates the presence of an antigen of interest in the sample. The liquid of the sample migrates through the membrane very fast, which makes it possible to detect the presence or absence of antigen within 15 minutes as shown below image. Lateral flow immunoassays represent a well-established and very appropriate technology when applied to a wide variety of point-of-care (POC) or field-use applications. Benefiting from its rapid test procedure and naked eye visible characteristics, lateral flow immunoassays have achieved broad penetration in a variety of markets, including agriculture, medical diagnostic, food safety and so on. - Reference -

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