Development and application of a sandwich ELISA method for detection of N protein in SARS-CoV-2 inactivated vaccine

Objective: To develop a sandwich ELISA method for detection of N protein in SARS-CoV-2 inactivated vaccine, and to further validate and primarily apply it for N protein qutification. Methods: The indirect ELISA method was used to assess the affinity of different anti-N protein antibodies by coating the recombinant N protein. Then the sandwich ELISA system was set up by using antibodies rN003 and rN002 as the capture and detection antibody, respectively. Also, the method for fully lysing virus to release all the N protein was confirmed. Validation of linear range, accuracy, precision, intermediate precision, specificity and LLD were obtained, and N protein content in 6 batches of SARS-CoV-2 inactivated vaccine was determined using this method. Results: N protein content has good linearty within the concentration range of 0.018~0.75 μg•mL-1 (R2>0.98), with the recovery of 80%~120% and CV <10%. N protein concentrations for 6 batches of samples accounted for 10%~20% of the total protein. All samples showed a good uniformity. Conclusions: The sandwich ELISA method for detection of N protein in SARS-CoV-2 inactivated vaccine was successfully developed with good linearty, accuracy, precision, intermediate precision, selectivity, and sensitivity, which can satisfy the N protein detection of SARS-CoV-2 inactivated vaccine.