Lateral Flow Assay is the device that is used for different types of testing by the detection of the target analyte, if present or not in the sample. Lateral Flow Assay devices are used globally for several benefits and one of the benefits is that they can be used for home testing. As far as home testing is concerned, one can detect diseases, infections, and also do the pregnancy test at home. Lateral Flow Assay tests are used to identify biomarkers in urine, saliva, blood, plasma, and other samples for diagnostic purposes. Conventional LFAs yield semi-quantitative or qualitative results, requiring the use of specialized instruments to detect quantitative results. LFA is a testing method that uses paper to detect and quantify analytes in complex mixtures. The sample is placed on a test device, and the results are usually available within five to thirty minutes.
The components of the lateral flow devices are sample pad, conjugate pad, nitrocellulose membrane, and adsorbent pad. When the sample or matrix is put onto the sample pad it flows towards the conjugated pad where the biological antigens and antibodies start binding and the particles from the sample pad mix with the nanoparticles on the conjugated pad. Next, they move towards the membrane. Here the nanoparticles become analyte bound and on the Lateral Flow Assay device two lines are the test line and the control line. These nanoparticles will start to move across either the test line or the control line.
The test line consists of the immobilized nanoparticles that can combine with the particles on the conjugated pad to show the presence of the target analyte. However, from the test line, the fluid passes to the control line. The Control line consists of the affinity ligands that work to bind the conjugate particles with the analyte or without the analyte to show that the lateral flow assay device is working fine and properly. Now, after the fluid has been passed from both the lines i.e. test line and control line there is an adsorbent pad. Adsorbent pad works to adsorb all the excess liquid. Since a small and controlled amount of matrix is needed, therefore, it ensures to allow the flow of liquid that is required only.
While doing the pregnancy tests on the lateral flow devices that are two formats i.e. competitive format and sandwich format. The use of competitive format is for the detection of the analytes in case that the antibodies or the analyte are not enough for the multiple binding. In the competitive format, there are analyte molecules in the test line and a protein-analyte complex with the conjugate pad that tells abt the presence or absence of analyte. In this type of format, if the target analyte is not present, the conjugates will get bind to the test line. Coming on to the sandwich format of the lateral flow assay devices pregnancy test, this format is used for the detection of the target analytes, if present or not Further, these larger analytes must have the epitopes. Also the antibodies in two biding sites of this format bind in a way that one analyte will bind with the conjugated particles and the other analyte with another binding test that will be used for the lateral flow Assay's test line. However, if the target analyte is detected it will bind with the antibody-nanoparticle conjugate and yield the desired results. Also, an important point is that in the sandwich format of the latera Flow essay device for the pregnancy test, the colored line appears that means the result is positive, However, in the competitive format there will be the absence/disappearance of the colored lines on the device which means that the results are positive. in the lateral flow assay device works this way for doing a pregnancy test on it.
For the analysis of the lateral flow assay test, it is important to note that tests would be either in the signs that can be read by the naked eye and are also easily understandable. To ensure the sensitivity of the lateral flows assay device it is important to have the strongest signal that is possible to the extent. If there are larger particles the binding would be stronger but if they will be too large there will be a constraint in the flow of the sample. The results of the lateral flow assay device will be either in the following formats i.e. qualitative, semi-qualitative, and quantitative. However, the pregnancy tests on the lateral flow assay device, will show the qualitative results i.e. Yes or No. In the Lateral Flow Pregnancy Test, the analysis and the results are based on the HCG analysis. HCG stands for Human chorionic gonadotropin that is composed of the trophoblast cells. When the matrix is put on the sample pad of the device, the Human chorionic gonadotropin is bound to the gold nanoparticles that are combined with the test antibody and conjugated antibody. Because this is the typical aggregation of hCG in your urine, the concentrations of it vary depending on when you take the test. The detection limit for the test is frequently between 20 and 100 mIU/mL. Talking about the quantitative diagnostics, the intensitive of the test line is determined by the set standard i.e. called the calibration standard and in this, the analytes are converted into the concentration value. For determining the accurate results, it is suggested to use the strip reader to read the results on the Lateral Flow Assay device.
Conclusion
Lateral Flow Assay devices are cost-effective and easiest to use devices that are being used by developed and developing countries. Moreover, lateral flow devices are one of the most reliable test methods for pregnancy tests as they yield true results and almost everyone knows how to use them at their convenience. The Lateral Flow Assay device is the top-most for doing any kind of test at home.
References
https://nanocomposix.com/pages/introduction-to-lateral-flow-rapid-test-diagnostics
https://studentsxstudents.com/pregnancy-tests-covid-19-testing-an-explanation-of-lateral-flow-assays-b45282ebdda4
