Kids will always find clever ways to get out of school, and the last trick is to simulate a positive Covid-19 lateral flow test (LFT) using carbonated drinks. [Videos of the trick have been circulating on TikTok since December and a school in Liverpool, UK, recently wrote to parents to warn them about it.] So how do juices, cola, and sneaky kids trick the tests, and is there any way to tell a false positive result from a real one? I tried to find out.
First of all, I thought it was better to check the claims, so I opened bottles of cola and orange juice, then dropped a few drops directly on the LFTs. Indeed, a few minutes later, two lines appeared on each test, supposedly indicating the presence of the virus that causes Covid-19.
It’s worth understanding how the tests work. If you open an LFT device, you will find a strip of paper-like material, called nitrocellulose, and a small red pad, hidden under the plastic casing below the T line. Absorbed on the red pad are antibody that bind to the Covid-19 virus. They are also attached to gold nanoparticles (tiny particles of gold actually appear in red), which allows us to see where the antibodies are on the device. When you perform a test, you mix your sample with a liquid buffer solution, making sure that the sample remains at optimal pH, before you drop it onto the strip.
The fluid absorbs the nitrocellulose strip and picks up the gold and antibodies. These also bind to the virus, if it is present. Higher on the strip, next to the T (for testing), there are more antibodies that bind to the virus. But these antibodies are not free to roam – they are stuck to the nitrocellulose. As the red smear of gold-labeled antibodies passes this second set of antibodies, these also take hold of the virus. The virus then binds to both sets of antibodies – leaving everything, including gold, immobilized in a line next to the T on the device, indicating a positive test.
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The gold antibodies that have not bound to the virus continue to the strip where they encounter a third set of antibodies, not designed to pick up Covid-19, stuck to the C line (for control). These trap the remaining gold particles, without having to do so via the virus. This last line is used to indicate that the test worked.