Social media users are claiming that fruit juices and Coffee produce positive test results for COVID-19. However, it is not the case. They have failed to understand how Lateral Flow devices (LFD’s) work. Many of the users have tested LFDs with substances other than saliva to prove they are ineffective. They include examples of the devices showing two pink lines, indicative of a positive COVID-19 result. However, this is misleading.
Professor Mark Lorch who is the professor of public engagement and science communication and interim head of department for chemistry, biochemistry and chemical engineering at the University of Hull told that:
“ The beverages and other solutions do not COVID-19 virus”.
He explained the working of Lateral Flow devices that the positive results disclose something else instead, “Instead, the acidity of the juices, soft drinks, coffee etc. disrupt the delicate antibodies on the test devices and so corrupt the test results”, he explained.
Working of LFT devices:
It’s worth understanding how the tests work. 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. Absorbed to the red pad are antibodies that bind to the COVID-19 virus. 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. 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.
The fluid picks up the gold and antibodies and binds to the virus, if present.
How do the drinks test positive ?
The question arises here that how do the drinks test positive then, one possibility is that the drinks contain something that the antibodies recognise and bind to, just as they do to the virus.
A much more likely explanation is that something in the drinks is affecting the function of the antibodies. 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. 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. 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. Maintaining an ideal pH for the antibodies is key to the correct function of the test
