A highly sensitive nanobody-based immunoassay detecting SARS-CoV-2 nucleocapsid protein using all-recombinant reagents

Antigen tests have been crucial for managing the COVID-19 pandemic by identifying individuals infected with SARS-CoV-2. This remains true even after immunity has widely attained through natural infection and vaccination, since it only provides moderate protection against transmission is highly permeable to emergence of new virus variants. For this reason, widespread availability diagnostic methods essential health systems manage outbreaks effectively. In work, we generated nanobodies nucleocapsid protein (NP) an affinity-guided selection identified a nanobody pair that allowed detection NP at sub-ng/mL levels in colorimetric two-site ELISA, demonstrating high value clinical samples. We further modified assay using nanobody-NanoLuc luciferase chimeric tracer, resulting increased sensitivity (detection limit = 61 pg/mL) remarkable improvement performance. The luminescent was finally evaluated 115 nasopharyngeal swab Receiver Operating Characteristic (ROC) curve analysis revealed 78.7% (95% confidence interval: 64.3%-89.3%) specificity 100.0% 94.7%-100.0%). test allows parallel large number untreated samples, fulfills our goal producing recombinant reagent-based can be reproduced low cost other laboratories expression capabilities, aiding build capacity.