Chemist Breaks Down How At-Home Covid Tests Work

[Narrator] Over the past two years

you've likely taken a COVID rapid antigen test

and you probably know what to do.

Swab.

Swirl.

And wait for results.

A unique biochemical reaction involving saline,

tiny particles of gold

and paper with antibodies

is helping to give us quick and relatively accurate results.

Never felt more attractive in my life.

Okay. Three, four Mississippi, five. [laughs]

[Narrator] Today, Kate is taking a COVID test

while explaining the biochemical reactions.

[calm music]

15 Mississippi.

I'm gonna go the other way.

Okay, now I'm gonna do the disgusting thing,

and stick this in the back of my throat.

Ugh.

Okay, okay, okay, that's all I can do.

So an epidemiologist named Michael Mina,

he is strongly suggesting

for this particular variant, for Omicron,

that you swab in the back of your throat

and your nose if you're gonna do the rapid test.

And so we're just looking for the highest viral load.

Some people are swabbing their nose and getting a negative

and then they swab their throat and getting a positive.

And that is just supporting the fact

that Omicron is definitely living in our throat.

We are having a high viral load there

and it's more easily detected if you swab there.

[Narrator] Once we've collected our sample

the chemistry starts to begin

and molecular forces take our sample in a buffer solution.

So the buffer solution is almost entirely salt water.

And so it's like 99.7% salt water,

which really sodium chloride in water.

On top of that

we have a conjugate acid and a conjugate base.

And so these are two different versions

of a phosphate molecule.

One is called sodium hydrogen phosphate

and the other one is called potassium dihydrogen phosphate.

And they lock the solutions pH into about a pH of 7.4.

[Narrator] This is where the chemistry comes in.

The acid and the base and the buffer solution

create a conjugate acid-based pair.

A conjugate acid and base are two different molecules

that are almost identical except for one hydrogen atom.

So one piece has the hydrogen atom.

One piece does not.

And buffer solutions are resistant to big changes in pH.

So if an acid comes along

the conjugate base is going to eat that up

and keep it at a pH of 7.4.

If a base comes in

the conjugate acid is gonna eat that part up

and again lock the pH at 7.4

[Narrator] That pH of 7.4.

The same pH as our blood,

helping to mimic the conditions of the human body.

One, two, three, four.

Beautiful.

[Narrator] Now that our sample is locked in

with a pH of 7.4

we can see whether we are positive or negative.

And that tiny spot where it says S,

that's where nano particles of gold reside.

Such a tiny amount of gold in there.

You couldn't sell it.

You cannot see it.

You can't turn it into a necklace or anything.

It is absolutely minuscule.

The gold is connected to an antibody.

And so there's kind of like a chunk of gold

and an antibody right here.

And if that end protein from the COVID virus

is present in the specimen,

Antibody 1 is gonna reach out and grab it.

[Narrator] Those antibodies are immune responses

to a specific antigen.

An antigen is the part of the virus

that is easily distinguishable.

So technically pollen could be an antigen.

Any foreign body that comes

into your body could be an antigen.

But a lot of times we talk about it

in the context of a virus.

And so if gold nano particle,

plus Antibody 1, plus COVID virus,

goes up to that T level,

Antibody 2 now reaches out

and grabs onto that COVID virus

and locks it into place.

So you've got gold, Antibody 1, COVID,

and then Antibody 2 stuck on that T line.

And now, boom, you've got a color change.

So a positive test is gonna happen right away.

As soon as that gold nano particle reaches that T level

and the antibody grabs onto the COVID virus

you're going to see that color change.

Now a negative test is essentially

a lack of a positive test.

And so what we're doing is just making sure

that in that allotted time

that T level never changes colors.

[Narrator] Now, there are some caveats

as to how accurately your test results come in.

Number one would be, if you swabbed correctly.

Lab scientists are getting the best results

because they know exactly how to perform these tests.

Followed by healthcare workers, they're second.

And then the third is the regular,

the rest of us that are just at home doing that.

Second thing that could detect your test

is your viral load.

So how much of that virus is actually sitting in your body.

[Narrator] And there's also ways people cheat the test.

In fact, a few TikToks have shown tests

with Coca-Cola's Zero Sugar,

strawberry juice or Monster Energy get a positive result.

These rapid tests are very pH sensitive.

That's why we use the buffer

to lock our sample into a pH of 7.4.

If we start introducing something like soda

which has a pH around 3,

or something like juice which has a pH around 4,

you're going to immediately mess with the pH of your sample

and that's going to completely negate

the result of the test.

And you might get a false positive.

You might get a false negative,

but it's just definitely not accurate.

So parents out there,

if your kid is cheating by using soda or something

to get a false positive, to get outta class,

the best way you can figure that out

is grab that original buffer solution,

shake it over that T line,

and if it was messed with, if soda or juice was used,

you're going to immediately see it switch back

and you'll get the accurate result

which would likely be a negative.

Now for the first time,

everybody, no matter who you are,

what your look like, what your gender is,

you are actually going through these at home tests.

And I think that's really valuable

and kind of neat that we're all at home scientists.

I truly hope we use this technology

to move forward to the flu.

That would be my goal.

If we could use this every single season,

if you think you have the flu,

test yourself before you go outside,

wear a mask still.

I would love to see that moving forward

cause' that's just gonna be incredibly helpful

for our public health.