Something to think about the next time you get a RAT test.
Everyone has seen one and there’s a good chance you’ve even used one yourself. In fact, I used a rapid antigen test (RAT) just the other day.
I said to my wife, “What a simple and ingenious little device”. And she said, “They’re not that special, they work just like the device for a home pregnancy test.”
And, of course, she’s absolutely right!
I just hadn’t made the mental connection that they’re based on the same technology. Naturally, this piqued my curiosity and I had to find out how RATs work.
I’ve left out a lot of the technical jargon, so here’s a simple explanation.
The key component (or the “magic”) in a RAT kit is the lateral flow device (LFD). That’s the plastic device you squeeze your liquid sample into and wait for the lines to appear. The device is completely self-sufficient and it has all the required reagents in the device to do the test.
Once you add your sample to one end of the device (via the hole), a porous material wicks the sample along the strip to the other end of the device.
Sandwich assay and two line LFDs
A sandwich assay is probably the most common method used to test for COVID-19 and the LFD will have two result lines: a test (T) and a control © line.
As the liquid sample flows across the device, it encounters three different capillary pads, each doped with different reactive molecules. A fourth and final pad at the very end of the device acts as a sponge to hold any excess fluid.
The conjugate pad (the first pad) is laced with very specific antibodies. If the targeted antigen (viral molecule) is present, it’ll be tagged with a colour laced antibody. The analyte (a solution whose chemical constituents are as yet unidentified) will continue to flow along the strip onto the next pad.