For both test and control line detection conjugates, 400 nm carboxylic blue latex beads (Cat. No. CAB400NM, Magsphere, Pasadena CA, USA) were washed three times with 0.1 M MES buffer, pH 6. Then, latex beads were activated using EDC/NHS coupling reagents at 0.15 and 10 mg/mL respectively for 30 minutes. Afterwards, the blue latex particles were conjugated in 1× PBS, pH 7.2 to various antinucleocapsid antibodies at a w/w ratio of 30:1 and 10:1 (bead:antibody) for test and control line antibodies, respectively, for three hours. Finally, latex conjugates were quenched using 0.1 M ethanolamine before being washed and blocked with 6% (w/v) casein, final concentration 1.2%, overnight. The latex conjugates were stored in buffer containing 50 mM borate and 1% casein, pH 8.5. The latex conjugates were quantified using the spectrophotometer by measuring absorbance at 660 nm and comparing to absorbance of unconjugated beads.