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Lateral flow assay (LFA), also known as lateral flow immunochromatographic assay, is a simple bioanalytical tool that allows for rapid detection of analytes within minutes. LFAs have gained immense popularity in recent years due to their user-friendliness and suitability for point-of-care testing (POCT). In this article, we discuss the basics of LFA, its working principle, application areas and future potential.
What is Lateral Flow Assay?
Lateral flow assay refers to a bioanalytical technique in which a liquid sample flows laterally across a porous membrane by capillary action. The membrane is pre-treated with reagents that allow for specific reactions with analytes in the sample. These reactions result in a visible signal that indicates a positive or negative result.
In simpler terms, an LFA strip contains a sample pad, conjugation pad, membrane and absorbent pad. A liquid sample applied to the sample pad flows through the strip via capillary action and reacts with colored particles attached to detection antibodies in the conjugation pad. These detection particle-antibody complexes then flow laterally along the membrane where they bind to immobilized capture antibodies, generating a visible signal line. Unbound particles continue their migration to the absorbent pad. The presence or absence as well as the intensity of the signal line determines the concentration of analyte in the test sample.
Working Principle
The underlying principles of LFAs rely on basic immunochemistry and lateral fluid flow dynamics. When a liquid sample containing target analytes is applied to the sample pad, the analytes bind to labeled detection antibodies or antigens coated on microspheres, microparticles or gold nanoparticles in the conjugation pad. These detection conjugates then flow laterally via capillary action along the membrane.
The membrane is usually nitrocellulose and pre-treated with a line of capture antibodies or antigens specific to the target analyte. As the detection conjugates pass over this test line region, they bind to the immobilized capture molecules, forming analyte-sandwich complexes that generate a visible colored line. The presence or intensity of this test line corresponds to the concentration of analyte in the sample.
Any remaining unbound detection conjugates continue migrating along the membrane and bind to a control line consisting of antibodies specific to the labeled microparticles. This control line ensures proper functioning and flow of the test. The absorbent pad soaks up excess fluid to terminate the flow. Within 10-30 minutes, clearly visible test and control lines indicate a positive or negative result that can be read with the naked eye.
Applications of Lateral Flow Assay
Infectious Disease Diagnostics
LFAs are widely used for diagnosing infectious diseases at the point-of-care. Rapid tests exist for detection of viruses like influenza, HIV, hepatitis B and C as well as bacteria such as streptococcus and mycobacteria directly in patient samples within 15-30 minutes. This allows for fast clinical decisions.
Pregnancy and Fertility Testing
Home pregnancy test kits employ LFA technology for fast and accurate detection of human chorionic gonadotropin (hCG) hormone in urine samples, which confirms pregnancy within minutes. LFA fertility test strips can also detect the luteinizing hormone surge to predict ovulation windows.
Toxicology and Drug Testing
On-site toxicology and drug testing is easily done using LFAs. Tests exist for quick analysis of samples like blood, urine and oral fluid for presence of narcotics, alcohol, benzodiazepines and other psychoactive substances. This enables immediate treatment and legal decisions.
Food Safety and Quality Testing
LFAs find wide application in food industry for monitoring food safety, quality, freshness and authenticity. Tests are available for pathogens, GMOs, allergens, veterinary drug residues, freshness biomarkers and more, to ensure food safety at various stages from production to consumption.
Environmental Monitoring
The portability, rapidness and simplicity of LFAs also make them suitable candidates for environmental monitoring. Tests exist for water quality parameters like heavy metals, pesticides, E.coli and coliforms to check for contamination on site.
Advantages and Future Potential
Simplicity and Ease-of-use
LFAs are highly user-friendly due to their simple one-step homogeneous assay format without need for specialized equipment or skilled personnel. This enables true point-of-care testing.
Rapidity and Portability
Results are generated very quickly within minutes, in contrast to conventional centralized lab methods taking days. Also, LFA tests can be performed anywhere due to their compact portable format.
Low Cost
LFA manufacturing involves simple procedures and inexpensive mass production techniques, keeping the unit costs remarkably low compared to other assays. This improves accessibility.
Multiplexing Capability
Advanced generation multiplex LFAs now allow simultaneous detection of 2-5 analytes in a single well or dipstick format through use of color-encoded immunoreagents, increasing information from single tests.
Mobile Health Applications
Integration of LFAs into smartphone cameras and apps enables objective quantitative analysis and telemedicine using eHealth platforms. This holds promise for decentralized healthcare delivery in remote areas.
With more automation and refinement, Lateral Flow Assay are expected to find many new applications in fields such as food safety monitoring, environmental biosurveillance, home healthcare, biodefense and more in the coming years. Their simplicity, rapidity and low-cost would especially benefit resource-limited settings worldwide. Overall, LFAs are envisioned to transform healthcare through ubiquitous point-of-care testing.
*Note:
1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
