How Does the New Coronavirus Test Work?

Derek Lowe's commentary on August 27, 2020, discusses the newly authorized Abbott “BinaxNOW”, which is a lateral flow assay, that should be familiar to anyone who’s seen a pregnancy test, but a flipped version. In this case, a nasal swab is taken, and several drops of solvent are used to put that sample onto the beginning of the absorbing strip inside the card. As it soaks up along the length of the strip, the sample will encounter a zone of antibodies that recognize the Np antigen, and these antibodies are also attached to nanoparticles of gold.

This gold-antibody-Np complex is carried along in solution further along the strip until it runs into another antibody zone, one that’s immobilized on the solid support and which will bind the gold-antibody-Np complex molecules tightly. That stops them in their tracks and allows the gold nanoparticles to pile up enough to be visible as a pink or purple line. Along the way, the sample has also crossed a zone containing another soluble gold conjugate species as a control, which gets carried along until it runs into another separate zone of immobilized antibodies specific to it.

The presence of a pink control line means that the test has been performed correctly; the absence of such a control line means that the whole test has been messed up somehow and needs to be run again.