How kids are spoofing Covid-19 tests with soft drinks

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 soft 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 fruit juices, cola and sneaky kids fool the tests, and is there a way to tell a false positive result from a real one? I tried to find out.

First, I thought it best to verify the claims, so I opened bottles of cola and orange juice, then dropped a few drops directly onto the LFTs. Sure enough, 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 testing works. 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 gold particles actually appear red), allowing us to see where the antibodies are on the device. When you perform a test, you mix your sample with a liquid buffer solution, ensuring that the sample remains at optimum pH, before pouring it onto the strip.

The fluid aspirates the nitrocellulose strip and picks up the gold and antibodies. These also bind to the virus, if present. Further up the strip, next to the T (for test), are other antibodies that bind to the virus. But these antibodies are not free to move – they are stuck to the nitrocellulose. When the red smear of gold-labeled antibodies passes this second set of antibodies, these also pick up the virus. The virus is then bound to both sets of antibodies – leaving everything, including the gold, immobilized in a line next to the T on the device, indicating a positive test.

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Gold antibodies that did not bind to the virus move up the band where they encounter a third set of antibodies, not designed to detect Covid-19, stuck at line C (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.

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