A magnetic bead immunoassay to detect human IgG reactive to SARS-CoV-2 Spike S1 RBD produced in Escherichia coli

Immunological assays to detect SARS-CoV-2 Spike receptor binding domain antigen seroconversion in humans are important tools to monitor the levels of protecting antibodies in the population in response to infection and/or immunization. Here we describe a simple, low cost and high throughput Ni2+ magnetic bead immunoassay to detect human IgG reactive to Spike S1 RBD Receptor Binding Domain produced in Escherichia coli. A 6xHis tagged Spike S1 RBD was expressed in E. coli and purified by affinity chromatography. The protein was mobilized on the surface of Ni2+ magnetic beads and used to investigate the presence of reactive IgG in the serum obtained from pre-pandemic and COVID-19 confirmed cases. The method was validated with a cohort of 290 samples and an area under the receiver operating characteristics curve of 0.94 was obtained. The method operated with>82% sensitivity at 98% specificity and was also able to track human IgG raised in response to vaccination with Comirnaty with 85% sensitivity. The IgG signal obtained with the described method was well correlated with the signal obtained when pre fusion Spike produced in HEK cell lines were used as antigen. This novel low-cost and high throughput immunoassay may act as an important tool to investigate protecting IgG antibodies against SARS-CoV-2 in the human population.

Magnetic bead-based ELISA allow inexpensive, rapid and quantitative detection of human antibodies against SARS-CoV-2

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.