For example, negatively charged parts of a protein will be attracted to positively charged areas.īut in acidic conditions, the protein becomes increasingly positively charged.
These structures are maintained by a network of many thousands of interactions between the various parts of the protein. Even a small change to the chains can dramatically impact a protein’s function. These chains fold up into very specific structures. Antibodies are proteins, which are comprised of amino acid building blocks, attached together to form long, linear chains. And this has a dramatic effect on their structure and function. So without the buffer, the antibodies in the test are fully exposed to the acidic pH of the beverages. The critical role of the buffer is highlighted by the fact that if you mix cola with the buffer – as shown in this debunking of an Austrian politician’s claim that mass testing is worthless – then the LFTs behave exactly as you’d expect: negative for Covid-19. Maintaining an ideal pH for the antibodies is key to the correct function of the test, and that’s the job of the liquid buffer solution that you mix your sample with, provided with the test. These are pretty harsh conditions for antibodies, which have evolved to work largely within the bloodstream, with its almost neutral pH of about 7.4. The citric acid in orange juice, phosphoric acid in cola and malic acid in apple juice give these beverages a pH between 2.5 and 4. A range of fluids, from fruit juice to cola, have been used to fool the tests, but they all have one thing in common – they are highly acidic. So they aren’t going to react to the ingredients of a soft drink.Ī much more likely explanation is that something in the drinks is affecting the function of the antibodies. There’s all sorts of stuff in the snot and saliva collected by the swabs you take from the nose and mouth, and the antibodies totally ignore this mess of protein, other viruses and remains of your breakfast. The reason antibodies are used in tests like these is that they are incredibly fussy about what they bind to. So, how can a soft drink cause the appearance of a red T line? One possibility is that the drinks contain something that the antibodies recognise and bind to, just as they do to the virus. This final line is used to indicate the test has worked. These trap the remaining gold particles, without having to do so via the virus. Gold antibodies that haven’t bound to the virus carry on up the strip where they meet a third set of antibodies, not designed to pick up Covid-19, stuck at the C (for control) line. The virus is then bound to both sets of antibodies – leaving everything, including the gold, immobilised on a line next to the T on the device, indicating a positive test. As the red smear of gold-labelled antibodies pass this second set of antibodies, these also grab hold of the virus.
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But these antibodies are not free to move – they are stuck to the nitrocellulose. Further up the strip, next to the T (for test), are more antibodies that bind the virus. The latter also bind to the virus, if present. The fluid wicks up the nitrocellulose strip and picks up the gold and antibodies. When you do a test, you mix your sample with a liquid buffer solution, ensuring the sample stays at an optimum pH, before dripping it on the strip.
They are also attached to gold nanoparticles (tiny particles of gold actually appear red), which allow us to see where the antibodies are on the device. Absorbed on the red pad are antibodies that bind to the Covid-19 virus. If you open up an LFT device, you’ll find a strip of paper-like material, called nitrocellulose, and a small red pad, hidden under the plastic casing below the T-line. It’s worth understanding how the tests work. Sure enough, a few minutes later, two lines appeared on each test, supposedly indicating the presence of the virus that causes Covid-19.
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So how are fruit juices, cola and devious kids fooling the tests, and is there a way to tell a fake positive result from a real one? I’ve tried to find out.įirst, I thought it best to check the claims, so I cracked open bottles of cola and orange juice, then deposited a few drops directly onto LFTs. Children are always going to find cunning ways to bunk off school, and the latest trick is to fake a positive Covid-19 lateral flow test (LFT) using soft drinks.
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