Fig. 3.

Indirect LFIA results showing specific interactions between the scFv-Fc antibodies and SARS-CoV-2 NP. (a) Schematic diagram of the indirect LFIA using SARS-CoV-2 NP as a capture probe. Protein A-conjugated CNB c bound strongly to all antibodies in the sample buffer. The antibody-protein A-conjugated CNB complex binds to the pre-immobilized SARS-CoV-2 NP on the test line in a manner dependent upon the affinity between the antibody and SARS-CoV-2 NP. (b) Bar graph showing the intensities of the test lines. After 20 min of sample flow, the intensity of the test line was measured using a portable LFIA reader, and the line intensities were normalized using the following equation: Relative intensity = (I_L– I₀)/I₀, I_L: Line intensity in the presence of antibodies, I₀: Line intensity in the absence of antibodies. (c) Results of the indirect LFIA. Three different NPs (derived from SARS-CoV-2, SARS-CoV, and MERS-CoV) were used for the test lines, and each scFv-Fc antibody was introduced onto the LFIA strip. After 20 min, the line intensities were measured using the portable LFIA reader (I_L: line intensity) and the LFIA strips were photographed with a smartphone.