Anti-coronavirusdisease-2019 (COVID-19; anti-severe acute respiratory syndrome Coronavirus 2 (SARS-CoV-2)) antibodies against nucleoprotein (NP) were purified from pig sera. Following the separation of the antibody fraction using a protein-A column, the final yield of the purified antibodies against SARS-CoV-2 NPs was estimated to be 0.26 ± 0.05 % (absolute amount of 143.4 ± 25.2 ng, n=5) from 1 mL of pig sera. The binding activities of the isolated antibodies were confirmed using immunoassay and immunostaining. Based on the specific binding activity to NPs, a quantitative assay was performed using a surface plasmon resonance (SPR) biosensor. From the doseresponse curve, the binding constant (Kd) was calculated to be 185 pM and the limit of detection was estimated to be 1.02 pM. The SPR biosensor with the isolated antibodies against SARS-CoV-2 NPs was applied for the detection of SARS-CoV-2, MERS-CoV, and CoV strain 229E in culture fluid.
