The best-known example of a lateral flow test is the home pregnancy test kit. A specified sample is collected and mixed with an extraction buffer (to be able to analyse the sample).
The sample is then applied to the sample well. In the presence of the correct amount of sample applied to the test cassette, the first red line ‘C’ will be visible.
In the presence of Covid-19 proteins (antigens) a red line would appear next to the ‘T’ also.