So do you know what the “rapid antigen” test is looking for, for COVID?
I can see what PCR is, as far as replicating a testable blob of DNA. What do you do then? Run a Blot?
Antigens are what your antibodies look for on the virus. There’s no amplification, so they aren’t as sensitive.
But they also depend on the virus still matching the sample, and most cold virii are quick mutators, so the test you develop today won’t pop hot in a year. Or maybe even in months. So there’s not much point in making them, unless you know you’re gonna be able to sell a lot of them, very quickly. And normal colds just aren’t severe enough (and have too many sources) to be worth bothering with making antigen tests.