RESUMEN
Serological assays are important tools to identify previous exposure to SARS-CoV-2, helping to track COVID-19 cases and determine the level of humoral response to SARS-CoV-2 infections and/or immunization to future vaccines. Here the SARS-CoV-2 nucleocapsid protein was expressed in Escherichia coli and purified to homogeneity and high yield using a single chromatography step. The purified SARS-CoV-2 nucleocapsid protein was used to develop an indirect enzyme-linked immunosorbent assay for the identification of human SARS-CoV-2 seroconverts. The assay sensitivity and specificity were determined analyzing sera from 140 PCR-confirmed COVID-19 cases and 210 pre-pandemic controls. The assay operated with 90% sensitivity and 98% specificity; identical accuracies were obtained in head-to-head comparison with a commercial ELISA kit. Antigen coated plates were stable for up to 3 months at 4{degrees}C). The ELISA method described is ready to mass production and will be an additional toll to track COVID-19 cases.
RESUMEN
Here we describe a novel immunogenic method to detect COVID-19. The method is a chromogenic magnetic bead-based ELISA which allows inexpensive and quantitative detection of human IgG or IgM antibodies against SARS-CoV-2 in serum or whole blood samples in just 12 minutes. As a proof of concept, we compared the performance of our new method to classical ELISA. Person correlation between optical densities obtained using the two methods was 0.98, the color intensity observed in the novel method correlated with antibody titers determined by classical ELISA. The novel magnetic bead-based ELISA correctly classified all 6 positive COVID-19 samples tested and showed 100% specificity as judged by the analysis of a cohort of 26 negative samples. The magnetic bead-based ELISA performed better than classic ELISA to discriminate COVID-19 positive serum with low antibody titer. The chromogenic magnetic bead-based ELISA method described here can be applied to both point of care and high throughput analysis. The method is readily adaptable to be used with other protein and peptide-based antigens.