LF - Lateral Flow

Lateral flow assays are widely used for point-of-care (POC) diagnostics, as they provide us with a quick and convenient method of detecting and measuring target analytes in samples.

There are two different types of lateral flow assay, and they are determined by your target.

• Sandwich assay: This assay is best suited for larger molecule analytes and has two antigen binding sites. A positive test is identified by the presence of a coloured line.

• Competitive assay: Mostly used for small molecule analytes which cannot bind two antibodies simultaneously and the indication of a positive test is the absence of a coloured line. An example of a competitive test is one used to test for drugs.

How the Lateral Flow works:

The assay is made up of four main components that are mounted over a backing card.

• Sample application pad: The pad is made up of cellulose or glass fibres and its function is to transport the sample to the next component.

• Conjugate pad: This pad releases the labelled conjugate upon contact with the moving liquid. The poorly prepared conjugate pad can affect the sensitivity of the assay.

• Nitrocellulose membrane: This is a critical stage which contains specific antigens/ antibodies immobilised and arranged in lines. Its function is to react with the analyte bound to the conjugated antibody.

• Absorbent pad: This pad is designed to absorb and collect the sample to prevent backflow. This pad is commonly made up of cellulose fibres.