Lateral flow assay (LFA) is a renowned diagnostic method for point-of-care (POC) testing and the reason is its low cost and ease of use. Lateral Flow Assay tests are used to identify biomarkers in any sample of urine, saliva, blood, plasma, etc. for diagnostic purposes. Conventional LFAs produce semi-quantitative or qualitative results, necessitating the use of specialized instruments to detect quantitative results. LFA is a paper-based testing method for detecting and quantifying analytes in complex mixtures. The sample is placed on a test device, and the results are presented within five to thirty minutes, approximately. LFAs' applications have broadened to a number of areas requiring rapid testing due to their cost-effectiveness and ease of manufacture.
The main characteristics of the lateral flow assay test are described next. First of all, they are disposable which means that they cannot be used time and again. Moreover, they are not washable. Once used they must be discarded. Secondly, they are economical and hence easily available and accessible. Third, they are robust in nature, which implies they can be stored at room temperature and have a shelf life of multiple years.
In recent times, there has been a growing market and need for point-of-care multiple diagnostic assays with comprehensive testing lines that allow for the rapid and concurrent detection of multiple analytes in point-of-care samples. Such assays (possibly a single LFA) should be smooth enough to perform without the support and assistance of a laboratory or groups of chemical analysts. LFAs are a preferred procedure because they are cheap to manufacture, simple to use, and, most importantly, widely recognized by end-users and regulatory authorities.
To mention types of lateral flow assay, there are two types of lateral flow assay tests. The types of the lateral flow assay test are based on the sample to be tested. The two main types have further subcategories. However, the first type of lateral flow assay is called Lateral Flow Immuno Assay and the second type of LFA is called Nucleic Acid Lateral Flow. Lateral flow immuno assay is categorized into two parts. One works on the basis of antibodies that act as the major part of the sample for the purpose of recognition. Whereas the second one has various recognizing agents or ingredients such as proteins, hormones, etc. The second type of Lateral Flow Assay is called Nucleic ACid lateral flow assay that helps in detecting amplicons that might have been created during polymerase chain reaction (PCR).
To develop the Lateral Flow Assay tests there are two methods that can be used. The first method is called a dipstick format whereas the second format is called a housed cassette. Their working is the same however they are dependent on the format, requirement of the market, matrix, and industry. In the lateral flow Assay Test, there are two formats that work. One is known as a sandwich and the second one is known by the name of the competitive format. The sandwich format is used for the detection of large analytes that would have either two binding sites or epitopes. The result of the sandwich format is in signal intensity on the spot of the test line that directs proportionally to the quantity of the analyte present in the sample. Eliminating the factor of the amount of analyte, if the control line has an antibody species it will have the power to bind the nanoparticles that will further lead to produce the signal of the control line to show the proper functioning of the lateral flow assay.
In the Lateral flow assay tests, the nanoparticles act as reporters in the result of a particular test. The result of the test can be read and analyzed through eyes that are also called qualitative or semi-quantitative or simply with the help of an instrument that is called quantitative reading. The lateral flow assay test is more workable and can produce true and desirable results when the size of the particles lies between 20 nm to 50 nm. For the resulting signal to be stronger, there are fluorescent particles that can be used for an even stronger signal in the production or outcomes of the sample as a result. Coming on to the competitive format of the Lateral flow Assay test, they are used for the detection of the analytes especially in the case when the antibody pairs are not available or the analyte is not big rather small for a multitude of antibody binding events. The test line usually contains the analyte molecule, which is ordinarily a protein-analyte complex, and the conjugate pad comprises the detection antibody-nanoparticle conjugate in the competitive format of the Lateral Flow Assay Test. If the target analyte is evident, the conjugate will bind to it, preventing it from binding to the analyte at the test line.
The analysis of the lateral flow assay tests is based on the three different types of results which might be confusing. However, the three main types of these results are qualitative, semi-quantitative, or quantitative. For the quantitative analysis of the lateral flow assay tests, the test line is compared to the standard that is known as the calibration standard, and then it is further converted into the concentration value of an analyte. However, for more accurate and to the point results the strip reader is recommended to be used for analyzing and reading the test.
Lateral Flow Assay Tests are one of the most widely used and globally known procedures that have unique properties. Moreover, Lateral Flow Tests have been a part of the great contribution towards the health care sector and also in the developing countries for which their role is immense. Their usage and advantages are not limited to the laboratories only; rather they are being used for home testing and have proven to be effective, easy to use, and cost-effective. Therefore, the lateral flow assay tests and their different types are helpful in different diagnostic purposes and they will continue to grow with other devices if they get merged together to bring more advancement and growth towards this sector.
References
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4986465/
https://nanocomposix.com/pages/introduction-to-lateral-flow-rapid-test-diagnostics#target
https://www.clinisciences.com/en/read/serological-tests-in-mycology-1190/lateral-flow-assay-lfa-2095.html
