Lateral flow test
It is a simple device intended to detect the presence of a target substance in a liquid sample without the need for specialized and costly equipment.
In essence, these tests run the liquid sample along the surface of a pad with reactive molecules that show a visual positive or negative result.
The control line contains affinity ligands which show whether the sample has flowed through and the bio-molecules in the conjugate pad are active.
After passing these reaction zones, the fluid enters the final porous material, the wick, that simply acts as a waste container.
[19] As the sample migrates through the assay it first encounters a conjugate, which is an antibody specific to the target analyte labelled with a visual tag, usually colloidal gold.
The majority of sandwich assays also have a control line which will appear whether or not the target analyte is present to ensure proper function of the lateral flow pad.
[2] The rapid, low-cost sandwich-based assay is commonly used for home pregnancy tests which detect human chorionic gonadotropin, hCG, in the urine of pregnant women.
Handheld diagnostic devices known as lateral flow readers are used by several companies to provide a fully quantitative assay result.
By utilizing unique wavelengths of light for illumination in conjunction with either CMOS or CCD detection technology, a signal rich image can be produced of the actual test lines.
Using image processing algorithms specifically designed for a particular test type and medium, line intensities can then be correlated with analyte concentrations.
Reducing variations in the capillary pumping of the sample fluid is another approach to move from qualitative to quantitative results.
Recent work has, for example, demonstrated capillary pumping with a constant flow rate independent from the liquid viscosity and surface energy.
[28][29] Lateral flow assays have a wide array of applications and can test a variety of samples including urine, blood, saliva, sweat, serum, and other fluids.
The broad applications of rapid test can be realized because of their simplicity accompanied by high quality analytical production.
[30] Other uses for lateral flow assays are food and environmental safety and veterinary medicine for chemicals such as diseases and toxins.
[31] The systematic evaluation of lateral flow assays during the COVID-19 pandemic[32] was initiated at Oxford University as part of a UK collaboration with Public Health England.
A study that started in June 2020 in the United Kingdom, FALCON-C19, confirmed the sensitivity of some lateral flow devices (LFDs) in this setting.
