Find out more, call us now: +44 (0) 1234 419430, or email info@rapivd.com
Lateral Flow and Rapid IVD
Contract Research, Development & Manufacture
Working with you when results really matter
Lateral Flow Tests - A Beginner's Guide
The simplicity of lateral flow tests are one of the reasons why they are increasingly popular as a way to test, monitor, detect and assess a huge range of biomarkers.
The simplicity hides a sophisticated blend of science and engineering that is further obscured by wall of technical vocabulary that is unfamiliar to most.
This is our attempt to simplify the science and the language to make it more accessible to more people.
Background
The Basics
Think of a lateral flow test as a small chemistry set. You put in a fluid containing your sample at one end and as the fluid flows along the test strip, it encounters a variety of chemicals (reagents) that are designed to react in different ways depending on what is in the sample. There are invisible lines on the test strip that capture some chemicals if the target substance is present – or pass if it’s not.
Easy to Use
Lateral flow tests are simple to use. They are often described as point-of-care or POC tests, because they can be used where required and can be administered by non-specialists. Other types of tests exist that require a professional to perform, often in a specialist place such as a clinic and the tests are run in a sophisticated environment such as a laboratory.
Familiar Technology
The first ‘at home’ lateral flow test was invented in the UK in the 1980’s. It is still the world’s most popular pregnancy test, Clearblue.
Lateral flow tests also played an important role in detecting signs of the covid virus during and immediately after the pandemic in the early 2020’s.
Versatility and Growing Popularity
The technology can be adapted to detect, test, measure and monitor a huge variety of biomarkers, such as:
-
Viruses
-
Proteins
-
Contaminants and pollutants
-
Hormones
-
Allergens
-
Bacteria
Best known for being helpful in diagnosing illnesses and health conditions, lateral flow tests are also used in animal health, food manufacturing, sports science, environmental monitoring, agriculture, law enforcement, defence and occupational health.
Lateral flow devices are increasingly popular because constant advances in the technology continue to improve the accuracy and reliability of the tests. They are cheap to manufacture, light to transport, easy to use and provide a result while you wait.
Strap in... this could get bumpy
Some tests are more complex than others, but a traditional lateral flow test works like this:
How it Works
The Sample
Preparation
The biomarker being detected is known as the target or analyte. This may (or may not) be present in the substance being analysed, this is the sample.
The sample could be one of several substances, the most common in humans are saliva, blood, nasal mucus and urine.
Sometimes, the sample needs to be dissolved or diluted to run effectively along the test strip, this fluid is known as the buffer.
Antibodies
Antibodies & Labels
Antibodies are central to how the test works. These need to be selected for their ability to attract and bind to some substances, but not others.
One of the antibody types is a pair, often referred to as the alpha and beta. The alpha is attached to a label which is normally a gold or polymer nanoparticle.
The label provides a visual indication of where the particles are concentrating along the test strip and the labelled antibody is known as the conjugate.
The conjugate is contained on a pad that is positioned after where the sample will be deposited, but before the test line.
Labels
The Test Strip
What looks like a piece of paper is actually several layers of different materials with a backing card at the base and a nitrocellulose strip through the middle which is overlapped by a sample pad at the start of the strip and a wicking pad at the end.
Each layer is selected for specific properties such as release rate, flow quality, printable precision and fluid retention.
Analyte Binding
Analyte Meets Conjugate
When the sample is placed onto the strip, it moves laterally and meets the conjugate (antibodies already bound to a label), where one of two things happen.
If the analyte is present in the sample, it binds to the labelled antibody and is carried along the strip to the test line.
If the analyte is not present, the conjugate moves to the test line without binding.
...or not
Test Line
The Analyte Trap
The test line contains the beta antibody and is anchored on a strip of nitrocellulose. If the analyte has attached to the labelled alpha antibody (conjugate) the beta antibody will also bind to the analyte and hold it in place. Not every labelled antibody will bind successfully and the remainder will move along to the control line.
With no analyte, there is nothing that can be trapped by the beta antibody and the conjugate will simply wash past the test line.
Keeping Control
The control line is also anchored to the nitrocellulose. It contains a different antibody (anti-species) that will bind to the conjugate, so any conjugate not already captured at the test line, will get captured at the control line.
If the control line doesn't capture anything, the test has not worked as intended and is invalidated.
Control Line
Wicking Pad
Flood Defender
The remaining fluid is soaked up by another pad at the end of the strip. This acts as a sponge or towel and makes sure that the test doesn’t get flooded by the sample.
Run Time
Compared to other diagnostic tools, lateral flow tests are rapid.
Some tests can provide a result within seconds, others take several minutes. Much depends on the sensitivity of the test and the quantity of the analyte in the sample. Most tests take between 5 and 20 minutes to provide an accurate result.
Speed
Well Done
If you made it this far and have a marginally better understanding of how lateral flow tests work, many congratulations.
The unfortunate thing is that there are very many variations and exceptions to the version described above.
Lateral flow technology looks simple - but it is incredibly complex. New materials, reagents, peripheral technologies and design techniques continue to improve the range of usage, accuracy and reliability of this neat little wonder tool.