lateral flow test

lateral flow test, method for the rapid detection and quantification of chemicals and other substances (analytes) in liquid samples from biological, environmental, and other sources. Lateral flow tests are highly versatile and can be applied in a variety of settings to detect the presence of a specific analyte. Lateral flow test devices, despite their different applications, share a basic design, which consists of a sample pad, a conjugate pad containing molecules that attach to the target analyte, a nitrocellulose membrane containing test and control bands, and an adsorbent (or wick) pad.

A lateral flow test is performed by first applying a liquid sample to the sample pad of the testing device; examples of liquid samples include blood, plasma, saliva, serum, and urine. The sample pad acts as a filter, removing unwanted matter, such as red blood cells, from the sample as it moves toward the conjugate pad. The conjugate pad contains coloured or fluorescent nanoparticles, each of which is attached to an antibody capable of detecting the analyte of interest. As the sample liquid comes into contact with the conjugate pad, the nanoparticles mix with the sample; analytes of interest in the sample will become bound to the antibody on the nanoparticles. The nanoparticles then flow through a nitrocellulose membrane, passing across the test and control lines.

When target analytes are present in a test sample, the analyte-bound nanoparticles attach to immobilized proteins in the test strip. This binding generates a visible signal, which indicates a positive result. As the liquid in the sample flows farther across the strip of the test device, it eventually reaches the control line, which contains molecules that have an affinity for the nanoparticles in the test, regardless of whether they are bound to the target analyte; the visible signal generated at the control line confirms that the test device is functioning correctly.

Lateral flow tests are perhaps most widely used in medicine, being convenient for rapid diagnostic testing particularly in hospitals, clinical laboratories, and at-home settings. Tests are available for the detection of a wide array of analytes, including antibodies, antigens, and gene products. Tests that detect the presence of an infectious agent specifically may be referred to as lateral flow immunoassays, while those that detect components of DNA or RNA are sometimes described as nucleic acid lateral flow assays. Examples of lateral flow immunoassays are viral antigen tests designed to detect SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19). Other fields in which lateral flow tests are used include environmental health, food safety, veterinary medicine, and quality control; in such settings, lateral flow tests may be used to screen for agents such as toxins, pathogens, and pollutants.