Table 1.

Checkerboard titration of rSARS-CoV-2-N based IgG ELISA

	200 ng/well	100 ng/well	50 ng/well	25 ng/well	12.5 ng/well
P 1:100	2.953	2.803	2.561	2.182	1.699
N 1:100	0.326	0.318	0.279	0.242	0.204
P/N	9.058	8.814	9.179	9.0165	8.328
P 1:200	2.627	2.411	2.022	1.597	1.34
N 1:200	0.28	0.264	0.259	0.236	0.173
P/N	9.382	9.133	7.807	6.767	7.746
P 1:400	2.095	1.899	1.592	1.051	0.874
N 1:400	0.254	0.196	0.129	0.106	0.04
P/N	8.248	9.689	12.341	9.915	21.85
P 1:800	1.228	1.038	0.797	0.686	0.567
N 1:800	0.215	0.193	0.17	0.084	0.032
P/N	5.712	5.378	4.688	8.167	17.719

The determination of optimal antigen coating concentration and dilution of serum

P: positive serum; N: negative serum; P/N: The ratio of the OD value of positive serum to negative serum