Lateral Flow Immunoassay (LFA), which is based on the specific binding of antigens and antibodies, is one of the immunoassay techniques renowned for its ease of use, portability, and speed. Since it is a simple operations immunoassay, the results can be attained quickly and without the use of complicated experimental machinery. LFA has been employed in multiple types of qualitative, semi-quantitative, and quantitative analysis applications for six decades.
General Principle
Central to the LFA is a concept reminiscent of a lock and key duo – a fitting analogy for its intricate workings. Imagine the detection of a specific protein in a blood sample. The capture molecules on the test line are the "locks," and the target protein is the "key." When the sample is applied, if the protein is present, it binds to the capture molecules on the test line, forming a visible line. The control line, which contains immobilized antibodies, serves as a validation of the test's functionality.
Fig 1. General components of the LFA and schematic description of each component of the immunochromatographic strip (Nuntawong P, et al. 2022)
Analysis
LFA can be used in qualitative, semi-quantitative and quantitative analysis, following are the differences of them:
Table LFA analysis type (Nuntawong P, et al. 2022)
| Analysis type |
Qualitative |
Semi-quantitative |
Quantitative |
| Detection method |
Visual observation |
Visual observation with comparison with standard |
Strip reader |
| Photo analysis software (optional) |
Scanner with photo analysis software |
| Results |
Yes/no results |
High-medium-low results |
Certain amount/concentration results |
| Results interpretation |
From presence/absence of the spot |
From estimated intensity of the spot |
From the intensity value which fits in the determination curve |
Application
Since LFA are so adaptable, several different fields are employing the following:
Medical Diagnostics: LFA is crucial in point-of-care diagnostics, enabling rapid screening for infectious diseases, pregnancy, cardiac markers, etc.
Food Safety: It is employed for the detection of allergens, contaminants, and pathogens in food products.
Environmental Monitoring: It is used to detect pollutants, toxins, and hazardous substances in air, water, and soil samples.
Drug Testing: LFA is a valuable tool for detecting drugs of abuse, both in clinical and forensic settings.
In summary, LFA have transformed the diagnostics landscape. It is indispensable in a multitude of fields due to the brilliant design, straightforward operation, and quick results. These assays provide a look into the future of diagnostics by utilizing the strength of biorecognition and capillary action. In this future, speed and accuracy go hand in hand, bringing crucial information to our fingertips in a matter of minutes.
Reference
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Nuntawong P, Putalun W, Tanaka H, Morimoto S, Sakamoto S. Lateral flow immunoassay for small-molecules detection in phytoproducts: a review. J Nat Med. 2022 Jun;76(3):521-545.
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