Rapid and quantitative detection of COVID-19 markers in micro-liter sized samples

Xiaotian Tan; Cory Lin; Jie Zhang; Maung Kyaw Khaing Oo; Xudong Fan

To compare the antibody's affinity towards the S1 protein of SARS-CoV-2 and SARS-CoV, we performed a side-by-side experiment for all antibodies under test 30 . The antibodies were CR3022, D001, D006, and D003. The first three antibodies were used as calibration standards in the IgG detection experiments and D003 was used as the detection antibody in the S1 detection experiments. Thanks to the simple protocol, our assay exhibits excellent intra-assay consistencies (see Fig. S4 as an example), thus ensuring highly reliable measurements. As shown in Figure 4 (B), these four antibodies have very different affinities towards the S1 protein of SARS-CoV-2. Note that the data for 1 ng/mL are not presented because the signal is not detectable for the three antibodies except D003 (the signal for D003 is very weak, see Figure S4 ). For the points within the linear dynamic ranges, the signal intensities with the strongest antibody (D003) are 6 -10 times higher than the weakest antibody (CR3022). For example, the signal intensities for these two antibodies at 250 ng/mL are 612 and 75.9, respectively. On the other hand, the lowest detectable concentration for D003 is 1 ng/mL and the lowest detectable concentration for CR3022 is 16 ng/mL. This can be another evidence for the difference in antibody's affinity. These observations agree with several recently published experiment results and our own preliminary results 24-26 and author/funder. All rights reserved. No reuse allowed without permission.