Diagnostic Performance of Three ELISAs for Detection of Antibodies against SARS-CoV-2 in Human Samples

Figure 1

Flowchart of the in-house ELISAs developed. ELISA plates were coated with 50 μL of the different antigens (N, S, or RBD fraction) at 2 µg/mL. After 16 hours, the plates were washed with PBS and blocked with a solution of PBS containing 3% non-fat milk and 0.05% Tween 20 for 1 hour. Next, the serum samples were diluted 1 : 50 in PBS containing 1% nonfat milk and 0.05% Tween 20 and added to plates coated with SARS-CoV-2 antigens. Following 2 hours of incubation, the plates were washed and incubated with horseradish peroxidase-labeled anti-human IgG secondary antibody (1 : 5000 dilution in PBS containing 1% nonfat milk and 0.05% Tween 20). The plates were then washed following 60 min incubation at 37°C, and 3,3′,5,5′-tetramethylbenzidine substrate was added. Two min later, stop buffer was added, and the absorbance values were measured at 450 nm wavelength using a microplate reader.