Detection of SARS-CoV-2 antigen by rapid antigen test (RAT)
The RT-qPCR-characterized samples were tested with the RAT Standard ™ Q COVID-19 Ag test (SD Biosensor, Inc., Republic of Korea). The standard ™ Q COVID-19 Ag test is an immunoassay that detects SARS-CoV-2 nucleocapsid protein by lateral flow technique. The test device consists of a membrane with control and test lines that are pre-coated with mouse monoclonal anti-SARS-CoV-2 antibody and anti-chicken IgG antibody, respectively. The mouse monoclonal anti-SARS-CoV-2 antibody conjugated with color particles are used as detectors for SARS-CoV-2 antigen. A colored test line would be visible, with various intensity, if SARS-CoV-2 nucleocapsid protein were present in the specimen. The test procedure was all done under BSL-2 following the manufacturer’s instruction. Briefly, the VTM, containing the NP and OP fluids, was first vortexed for 20 seconds and only 100 μl thereof was placed into the sample port of the cassette and incubated at room temperature for 15-30 minutes until reading the results in a blinded approach (i.e. without knowing the RT-qPCR results of the samples).