Fig. 1.

(A) Schematic of Neutralization LFA. Below each graphic is a representative image of a lateral flow strip demonstrating actual line density. Addition of non-COVID19-immune serum or plasma (top) does not block binding of RBD-beads (green particles) to ACE2 resulting in the RBD-bead–ACE2 complex creating a visible line. Addition of patient serum with moderate titer NAbs to the sample pad creates a weak line (middle). Addition of patient serum with high titer NAbs (> 1:640) blocks binding of RBD-beads to ACE2 such that no line is observed at the test location on the strip (bottom). Red control line represents capture of a mouse monoclonal antibody coupled to red beads. (B) Scorecard for measuring levels of NAbs . Red control line across from the “C” on the cassette indicates that the test ran properly and the green test line across from the “T” can be used to measure the ability of plasma or serum to block RBD on gold nanoshells from binding to ACE2. (0) represents patient serum producing a visually non-existent line with density units of 10,095 and an IC₅₀>500 (IC₅₀=1151); (1) represents patient serum with a line density of 132,503 and an IC₅₀ of 396; (2) represents patient serum with a line density of 317,156 and an IC₅₀ of 243; (3) represents patient serum with a line density of 645,040 6 and an IC₅₀ of 96.