Development of a Method for Detection of SARS-CoV-2 Nucleocapsid Antibodies on Dried Blood Spot by DELFIA Immunoassay

Abstract

Antibodies against the SARS-CoV-2 nucleocapsid protein are produced by the immune system in response to SARS-CoV-2 infection, but most available vaccines developed to fight the pandemic spread target the SARS-CoV-2 spike protein. The aim of this study was to improve the detection of antibodies against the SARS-CoV-2 nucleocapsid by providing a simple and robust method applicable to a large population. For this purpose, we developed a DELFIA immunoassay on dried blood spots (DBSs) by converting a commercially available IVD ELISA assay. A total of forty-seven paired plasma and dried blood spots were collected from vaccinated and/or previously SARS-CoV-2-infected subjects. The DBS-DELFIA resulted in a wider dynamic range and higher sensitivity for detecting antibodies against the SARS-CoV-2 nucleocapsid. Moreover, the DBS-DELFIA showed a good total intra-assay coefficient of variability of 14.6%. Finally, a strong correlation was found between SARS-CoV-2 nucleocapsid antibodies detected by the DBS-DELFIA and ELISA immunoassays (r = 0.9). Therefore, the association of dried blood sampling with DELFIA technology may provide an easier, minimally invasive, and accurate measurement of SARS-CoV-2 nucleocapsid antibodies in previously SARS-CoV-2-infected subjects. In conclusion, these results justify further research to develop a certified IVD DBS-DELFIA assay for detecting SARS-CoV-2 nucleocapsid antibodies useful for diagnostics as well as for serosurveillance studies.

Stability, enrichment, and quantification of total and HPV16-specific IgG present in first-void urine

“…Since PGMB contains magnetite (Fe 3 O 4 ), and PGMB-G samples are eluted in glycine, both of which are known to interact with Eu 3+ , potential non-specific binding and contamination of exogenous lanthanides may have affected the assay's reproducibility for samples enriched using the PGMB methods [38][39][40][41] . Therefore, the results of the PGMB for HPV16-IgG DELFIA and total IgG HTRF assays are reported as invalid [42][43][44][45] . However, it is worth noting that some correlations are observed for the PGMB enrichment when citric acid is used for elution instead of glycine, suggesting that there might be less interference with this assay for the PGMB-CA method.…”