Evaluations of serological test in the diagnosis of 2019 novel coronavirus (SARS-CoV-2) infections during the COVID-19 outbreak

Dachuan Lin; Lei Liu; Mingxia Zhang; Yunlong Hu; Qianting Yang; Jiubiao Guo; Youchao Dai; Yuzhong Xu; Yi Cai; Xinchun Chen; Kaisong Huang; Zheng Zhang

is the (which was not peer-reviewed) The copyright holder for this preprint . https://doi.org/10. 1101 /2020 length nucleocapsid antigen was expressed in engineering E. coli BL21 (DE3) strains and purified using 105 the Ni-NTA resin (Darui Biotech, China). Magnetic beads Magnosphere™ MS300 used in this study are 106 commercially available in the JSR Corporation, Tokyo, Japan. Recombinant nucleocapsid antigens 107 were coupled to these tosyl magnetic beads using the catalytic reagent solution (3M Ammonium 108 sulfate / 0.1M Borate buffer, pH9.5) according to the manufacture's instruction, and the resultant 109 beads were further blocked by 0.05% BSA for six hours at 37 °C. The following testing and detection 110 procedure was automated on a chemical immuno-luminescence analyzer ACCRE6 (Tianshen Tech, 111 Shenzhen, China). It was comprised of those following steps. 50 microliter pure serum was firstly 112 incubated with the magnetic beads that were coupled with antigens for 5 minutes at 37 °C. 113 Subsequently, the unbound substance was gently removed and then washed by Tris buffer for three 114 times. Alkaline phosphatase labeled anti-human immunoglobulin (50µg/ml) was added and further 115 incubated for 5 minutes at 37 °C in the Mes Buffer. After three times washing to remove unbound 116 materials, the lumigen APS-5 substrate (50ug/ml) was eventually added. Ultimately, the light signal 117 was measured by the photomultiplier in ACCRE6 (Tianshen Tech, Shenzhen, China) as relative light 118 units, and the whole testing can be completed in 23 minutes. Confirmed SARS-CoV-2 positive-serum 119 and negative-serum were used as controls in each set test. CC-BY-NC 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.