We performed bio-layer interferometry on recombinant nucleocapsid proteins (rNP analytes) for the purpose of selecting the most "native-like" rNP analyte for early LFA antibody screening. We first used the estimated R max of five different rNP analytes to quantify binding affinity against a random selection of 21 anti-nucleocapsid-protein (α-NP) antibodies from seven vendors (Rockland, Novus Biologicals, Sino Biological, Creative Diagnostics, Bioss, Fitzgerald, and MyBiosource). R max as a metric was calculated based on the theoretical saturation of 100% of the bound antibody (ligand) with the rNP analyte. In practice, analyte binding sites are not completely occupied, so the measured saturation value is typically less than R max . Moreover, because R max is proportional to analyte size, we were also able to detect aggregation or multimer formation in solution. Theoretically, the closer-and more predictable-values were to R max the more likely the analyte was to interact with antibodies as expected.