immunochromatographic

Immunochromatographic assays, commonly referred to as immunochromatographic tests, are rapid, often point-of-care immunoassays that use chromatographic principles to detect analytes on a disposable membrane. They typically provide qualitative or semi-quantitative results within minutes.

On a strip, a sample is applied to a sample pad and migrates by capillary action through a conjugate pad. The pad releases labeled antibodies (or antigens) that bind the target analyte if present. The complex moves along the nitrocellulose membrane to a test line where immobilized capture antibodies or antigens bind the complex, forming a visible signal due to the label, which may be colloidal gold, colored latex, carbon, or a fluorescent tag. A second control line captures excess labeled components to confirm the test ran correctly.

Most designs are lateral flow immunochromatographic tests. Formats include sandwich assays, suitable for larger antigens, and competitive assays, used for small molecules like drugs. Readout can be visual or assisted by a handheld reader for quantification.

Common applications include infectious disease testing, pregnancy testing, and veterinary or food safety screening. They are valued for speed, simplicity, portability, and low cost, enabling point-of-care decisions. Limitations include generally lower sensitivity and specificity than laboratory assays, potential cross-reactivity, and mainly qualitative or semi-quantitative results. Performance can be influenced by sample matrix, storage conditions, and strip quality.

Immunochromatographic techniques evolved from traditional immunoassays, with lateral flow formats gaining prominence in the late 20th century; pregnancy tests are among the earliest widely used examples. Ongoing improvements focus on sensitivity, specificity, multiplexing, and quantitative readouts.