Chemist Breaks Down How At-Home Covid Tests Work | WIRED

Over the past two years, you've likely taken a Covid rapid antigen test. A unique, biochemical reaction involving saline, tiny particles of gold, and paper with antibodies, is helping to give us quick and relatively accurate results. Dr. Kate Biberdorf, a chemist and author, explains the chemical process of the at-home tests (while taking one!) to explain exactly how it works.

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Twitter: @k8thechemist


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[andrewpetersen]

This is literally my Chemistry professor at the University of Texas I’m dying

[mariewesthott]

The reason false positives happen with soft drinks/ juice etc is that the low pH causes the antibodies to denature. When antibodies are denatured, they lose their structure and can become sticky. This happens because the bonds that were holding it in shape are no longer within the structure, and instead on the outer which makes the antibodies somewhat sticky.
These sticky denatured antibodies (both the ones labelled with the gold and the ones bound to the test region of the strip) bind each other at the test region and the accumulation of the bound gold particles (red/pink in colour) causes a false positive result.

In the video, she gets the false positive tests to change to negative by adding the buffer solution which returns the antibodies to their optimal pH. When the antibodies are returned to their optimal pH, they fold back into their desired structure (renaturation) and are no longer sticky. This means the antibodies that were sticking to each other at the test region become free, and the antibodies labelled with gold are washed off the test region.

Denaturation is not always reversible. If proteins are damaged beyond a certain point, they can not be returned to their optimal structure. So i wonder what would happen if a stronger acid like vinegar was used. Or alternatively, boiling/very hot water 🤔 someone test these please and let me know 😅

[timng]

if you want to know how the T line is colored, search labels lateral flow immunoassay. There are gold nanoparticles, Horseradish peroxidase+luminol, colorimetric based. The whole mechanism is actually very smart. A simple control test can be detecting a certain protein present in all human samples, if the sample is indeed legit, C line should light up. the problem with acidic samples like coca cola is probably releasing all the gold NPs regardless if there is a legit antigen, so both C and T line can light up.

[colunizator]

0:38
Aren't you supposed to first swab your throat and after that your nose ?
It's less disgusting

[jFranco]

Bold to blanket recommend swabbing the throat as none of the manufacturer’s have confirmed it will be more effective than following their known instructions which are there to prevent false positives. As you mentioned this test is highly pH sensitive and introducing a lot of saliva could throw it off depending on the test.

[CrownRider]

The nose swab shown is at the nose picking level. To get deep in the nose, one should hold the swab almost horizontal, and get at least 2 inches in. It's also better to swab the throat first and then the nose.

[xYasago]

Rapid lateral flow flu tests are already available with the same principle. They may not be sold direct to consumer but can easily seek one at a healthcare facility.

[nimatrix]

The pacing of the video was too quick for someone thats not familiar with thr field or topic. It felt very rushed

[Irishgui]

Great video and explanation!
I could NEVER swab my nose then my throat, I could almost heave at the thought 🤢
Throat>nose for me.

[casperr]

I hope we can at least replace the plastic with something else if we go forward with this massive scale use off single use items to test.

[lukas]

The buffer contains detergents that disintegrate the membrane of the virus, setting the nucelocapsidproteins free which are detected by the test.

[noodlesstyx]

Was expecting more of a ELI5 but at the fast pace and quick changes in the video, following was somewhat difficult and I still didn’t completely understand.

[onkelpappkov]

With the flerf crowd running wild on the interwebs, it might be better to make videos like these more extensive and easier to understand. Go into every detail of the subject to avoid people running around with questions and half-knowledge. Don't rush the video for budget reasons.

[whywhymusic]

0:36 did she actually put the swab in her mouth AFTER puttin it in the nose??

[KangJangkrik]

This is why my friend got positive when retake the test right after drank coca cola at train station. Thank you professor for the explanation

[noahjaybee]

What is expiring with the tests which seems to be about three months after purchase? Is the pH of the buffer or something else changing?

[MarkRLeach]

Good explanation of buffer action, but what was the gold doing? How did the color change exactly? I am a chemist and I don’t understand the “explanation”? Sorry!

[DuyTran-bbcq]

I kinda confuse on how to detect whether it is a false positive? so we grab the original buffer solution and pour it to the false result?

[mollymontana]

I wouldn’t swabbed my throat before my nose but I’m not a chemist ig

[GetOutsideYourself]

I've heard experts say don't swab the throat for tests that aren't made for it.