In simple terms the test cassette contains specially-engineered proteins (antibodies) that attach to the SARS-CoV-2 nucleoprotein (if it’s present in the sample) and these antibodies have a light-emitting chemical bonded to them that is read by the AFS-1000.
The more technical version is the reagent the swab goes into breaks the virus apart so the test can get at the part of the virus it’s looking for (the nucleoprotein).
After treatment with the reagent in the dripper, the sample is added to the sample well in the cassette. If the virus is present, its nucleoprotein and a labelled antibody in the cassette (monoclonal antibody against SARS-CoV-2 nucleoprotein) form an immune complex. This complex moves with the liquid along the nitrocellulose membrane in the cassette.
Further along the cassette there are other antibodies bound to the membrane. These attach to the n-protein / immunofluorescent antibody complexes thereby trapping them – but they do NOT trap any unbound antigen.
When the sample contains SARS-CoV-2 antigen it (along with the fluorescent marker that has bound to it) concentrates in the detection area of the cassette – and the AFS-1000 can read if the signal there is higher than the background. If it is the test is positive, if not it’s negative.
The reagent consists of test card, ID chip card, sample preservation solution (optional), dripper and swab. The test cassette consists of reagent strip and plastic case. The main components of the test strip are fluorescence labelled SARS-CoV-2 nucleoprotein monoclonal antibody and another nucleoprotein monoclonal antibody adsorbed to the detection area of the nitrocellulose membrane.
Anti-mouse immunoglobulin G polyclonal antibody is fixed in the quality control area of the nitrocellulose membrane. This proves that the cassette is working properly and ensures a faulty cassette cannot be misinterpreted as a negative test.
The main preservation solution is phosphate buffer (PBS, 50mM, ph7.2).