Introduction to Lateral Flow Rapid Test Diagnostics

Lateral flow assays (LFAs) are simple to use, disposable diagnostic devices that can test for biomarkers in samples such as saliva, blood, urine, and food. The tests have a number of advantages over other diagnostic technologies including:

❆ Simplicity: The simplicity of using these tests is unmatched – simply add a few drops to the sample port and read your results by eye a few minutes later.
❆ Economic: The tests are inexpensive - typically less than one dollar per test to manufacture at scale.
❆ Robust: The tests can be stored at ambient temperature and have a multi-year shelf life.

Billions of test strips are produced each year for the diagnosis of sexually transmitted diseases, mosquito-borne diseases, tuberculosis, hepatitis, pregnancy and fertility testing, cardiac markers, cholesterol/lipid testing, drugs of abuse, veterinary diagnostics, and food safety, amongst others.
A LFA is made up of a sample pad, a conjugate pad, a nitrocellulose strip that contains test and control lines, and a wicking pad.  Each component overlaps by at least 1–2 mm which enables unimpeded capillary flow of the sample.


To use the device, a liquid sample such as blood, serum, plasma, urine, saliva, or solubilized solids, is added directly to the sample pad and is wicked through the lateral flow device. The sample pad neutralizes the sample and filters unwanted particulates such as red blood cells. The sample can then flow unimpeded to the conjugate pad that contains strongly colored or fluorescent nanoparticles that have an antibody on their surface. When the liquid reaches the conjugate pad, these dried nanoparticles are released and mix with the sample. If there are any target analytes in the sample that the antibody recognizes, these will bind to the antibody. The analyte-bound nanoparticles then flow through a nitrocellulose membrane and across one or more test lines and a control line. The test line (labeled T in the image above) is the primary read-out of the diagnostic and consists of immobilized proteins that can bind the nanoparticle to generate a signal that is correlated to the presence of the analyte in the sample. The fluid continues to flow across the strip until it reaches the control line. The control line (labeled C in the image above) contains affinity ligands that will bind the nanoparticle conjugate with or without the analyte present in solution to confirm that the assay is working properly. After the control line, the fluid flows into the wicking pad which is needed to absorb all of the sample liquid to ensure that there is consistent flow across the test and control lines. In some tests, a chase buffer is applied to the sample port after sample introduction to ensure that all of the sample is transported across the strip. Once all the sample has passed across the test and control lines, the assay is complete and the user can read the results. 


The analysis time is dependent on the type of membrane used in the lateral flow assay (larger membranes flow faster but are generally less sensitive) and is typically complete in less than 15 minutes. 

Post time: Nov-27-2021