Development of a double-antibody sandwich ELISA for detection of SARS-CoV-2 variants based on nucleocapsid protein-specific antibodies

The COVID-19 pandemic, driven by the SARS-CoV-2 virus, has posed a severe threat to global public health. Rapid, reliable, and easy-to-use detection methods for SARS-CoV-2 variants are critical for effective epidemic prevention and control. The N protein of SARS-CoV-2 serves as an ideal target for antigen detection. In this study, we achieved soluble expression of the recombinant SARS-CoV-2 N protein using an Escherichia coli expression system and generated specific monoclonal antibodies by immunizing BALB/c mice. We successfully developed 10 monoclonal antibodies against the N protein, designated 5B7, 5F2-C11, 5E2-E8, 6C3-D8, 7C8, 9F2-E9, 12H5-D11, 13G2-C10, 14E9-F6, and 15H3-E10. Using these antibodies, we established a sandwich ELISA with 6C3-D8 as the capture antibody and 5F2-C11 as the detection antibody. The assay demonstrated a sensitivity of 0.78 ng/mL and showed no cross-reactivity with MERS-CoV, HCoV-OC43, HCoV-NL63, and HCoV-229E. Furthermore, this method successfully detected both wild-type SARS-CoV-2 and its variants, including Alpha, Beta, Delta, and Omicron. These findings indicate that our sandwich ELISA exhibits excellent sensitivity, specificity, and broad-spectrum applicability, providing a robust tool for detecting SARS-CoV-2 variants.