LFAs

Lateral flow assays (LFAs) are simple, point‑of‑care diagnostic devices designed to detect the presence of a specific analyte in a liquid sample without the need for specialized laboratory equipment. LFAs are immunoassays that employ antigen–antibody interactions to produce a visible signal, typically a colored line, on a porous strip.

How they work: the sample migrates by capillary action through a sample pad onto a conjugate pad containing labeled detector antibodies, often bound to colloidal gold or other colored particles. As the fluid moves along the nitrocellulose membrane, target analytes bind to immobilized capture antibodies at the test line, forming a visible line if the target is present. A separate control line captures excess detector conjugate to confirm the assay function.

Formats and readout: LFAs use sandwich assays for larger molecules and competitive formats for small molecules. Readouts are typically qualitative or semi-quantitative, based on line intensity; some designs employ portable readers for quantitative data.

Applications: LFAs are widely used in medical diagnostics (for infectious diseases, pregnancy testing, and biomarker screening), veterinary medicine, food safety, and environmental monitoring. They are valued for speed, simplicity, low cost, and suitability for at‑home, field, or resource-limited settings.

Limitations and considerations: sensitivity and specificity vary with antibody quality and sample type. False positives or negatives can occur due to cross-reactivity, improper storage, or matrix effects. Manufacturing quality and proper regulatory clearance (regional approvals) influence performance. The technology has evolved to improve sensitivity, multiplexing, and semi-quantitative readouts, expanding its utility while maintaining rapid results.