How pregnancy strip tests work/Lateral Flow Immunoassay/LFA/Rapid test strip

Welcome to Swim in Science #swiminscience #sowmyanrao #sowmyanagaraj How do pregnancy strips work? A pregnancy strip test works by measuring the amount of human chorionic gonadotropin (HCG) hormone in human urine. The hormone is produced by cells in the placenta, 6-12 days after conception. HCG is eliminated from the mother’s body through urine, and therefore urine is used as a sample during pregnancy test. The pregnancy test strips work on the principle of lateral flow immunoassay that detects the presence of a target substance in a liquid sample without the need for specialized and costly equipment. Parts of the LFA strip 1. Sample pad: An absorbent pad is present at the beginning of the strip where the sample is applied. 2. Conjugate release pad: This contains antibodies that are specific to the target analyte and are conjugated to colored particles such as gold nanoparticles. 3. Detection zone: This is a porous membrane such as nitrocellulose with specific biological components such as antibodies which are immobilized in lines called test line and control line. 4. Absorbent pad: A membrane attached at the end of the strip which absorbs excess reagents and prevents backflow of the liquid. Workflow of a pregnancy test strip A sample such as urine is applied on the sample pad which migrates through the capillary action of the membrane. As the sample migrates, it encounters the conjugate release pad where gold nanoparticle conjugated HCG-specific antibody is present. If HCG is present in the sample, it binds with the conjugate and migrates further, and enters the test line. The test line contains immobilized antibodies which are also specific to HCG. So, the HCG conjugate complex binds to the test line antibodies forming a sandwich. Increased binding at the test line results in the concentration of GNP that leads to the appearance of red color in the test line. The control line consists of immobilized antibody which is specific to HCG antibody. So the conjugate also gets concentrated in this zone resulting in red color. The control zone usually contains a sec ab specific to any IgG. So irrespective of the analyte, in both cases, that is presence or absence of pregnancy, the control line do appear indicating the proper flow of the test. So, a result is considered to be positive, red color appears in both the test and control lines. In contrast, the presence of red color only in the control zone is a negative result. References https://nanohybrids.net/blogs/nanoparticles/how-lateral-flow-assays-work https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4986465/ https://www.compoundchem.com/2018/11/09/pregnancy-tests/ BGM: Spring Flowers by Keys of Moon | https://soundcloud.com/keysofmoon Music promoted by https://www.chosic.com/free-music/all/ Creative Commons CC BY 4.0 https://creativecommons.org/licenses/by/4.0/