An immunochromatographic assay, commonly known as a lateral flow test, is a simple, rapid diagnostic device that uses antibodies immobilized on a membrane to detect specific analytes in a liquid sample. The result is typically displayed as colored lines on a strip.
Principle and Design
A lateral flow assay relies on capillary action to draw the sample across several functional zones. The sample is applied to a sample pad where it mixes with labeled antibodies on a conjugate pad. These detector antibodies are coupled to colored particles such as colloidal gold or latex beads. As the sample migrates along a nitrocellulose membrane, it encounters test and control lines with immobilized capture antibodies or antigens. If the target analyte is present, the labeled complex binds to the test line, forming a visible band. The control line captures the detector antibodies independently of the analyte and confirms that the fluid has flowed correctly. Membranes are backed by an absorbent pad that maintains capillary flow. Lateral flow assays can be configured in sandwich format for large antigens, competitive format for small molecules, or reverse assays for antibody detection. They do not require instrumentation, provide results within minutes and are easy to use. Sensitivity and specificity depend on the quality of the antibodies, the concentration of the analyte and the matrix, and they are generally lower than laboratory immunoassays such as ELISA.
Examples and Uses
Common examples include home pregnancy tests that detect human chorionic gonadotropin in urine, rapid antigen tests for influenza and SARS‑CoV‑2, and tests for malaria antigens such as histidine‑rich protein 2. Lateral flow devices are also used to detect antibodies to HIV, hepatitis C and syphilis, as well as drugs, toxins and allergens in food and environmental samples. In veterinary diagnostics, they screen for pathogens like parvovirus and feline leukaemia virus. Industrial applications include monitoring of mycotoxins in grain and verifying the presence of contaminants in milk. Their portability and ease of use make them suitable for point‑of‑care testing, field surveillance and low‑resource settings, although confirmatory laboratory tests may be required for definitive diagnosis. Lateral flow immunochromatographic assays provide accessible, rapid screening for a wide range of analytes. While less sensitive than laboratory techniques, their simplicity and speed have made them indispensable in public health, clinical care and food safety. Related Terms: Rapid antigen test, Immunoassay, ELISA, Colloidal gold, Point-of-care testing