Full Name: SARS-CoV-2 NP Ab ELISA Kit
Reactivity: Human
Sample Type: Plasma, Serum, Other Specimens
Sensitivity: Qualitative


Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was responsible for causing a global treat to public safety and health. The genomic RNA for this virus is made up from four structural proteins: spike glycoprotein (S), ion channel envelope protein (E), membrane protein (M) and the nucleocapsid protein (NP).

The NP is the last protein to be synthesized and it is responsible for encapsulating and spearheading the budding process, which causes the release of infectious nucleocapsids from cells. The formation of an infectious particle contains three main parts: a lipid bilayer, a protein shell and nucleocapsid. The lipid bilayer forms a membrane around the protein shell, forming the viral envelope while viral RNA encapsidates inside this shell. Once internalized into host cells, virions are then released when nucleocapsids push their way out of cells through pores in cell membranes.

Nucleocapsid protein function to help the viral RNA to assemble into a helical ribonucleoprotein complex (this is referred to as a nucleocapsid). This is possible because the NP can link with the M protein at the c-terminal endo-domain, this is needed for the process of coronavirus replication. There is evidence to indicate that NP may have the ability to self-assembly using its dimerization domains, it is still unclear if the SARS-NP has pathogenic properties in addition to its ability to pack viral RNA.

NP is a very small protein, which has 124 amino acids. It is the only known protein of coronavirus that does not contain a signal peptide and it has no discernible N-terminal or C-terminal domains. NP’s c-terminus is connected to the M protein by an irregular β-hairpin structure and contains a series of tyrosine residues, which are phosphorylated upon coronavirus infection. The first six tyrosine residues in NP perform negative control functions while the last four are responsible for positive control functions of NP and appear to be involved in RNA binding.


Human SARS-CoV-2 NP Ab ELISA kit can be used to determine amounts of total anti-SARS-CoV-2 nucleocapsid protein (NP) present in human serum and plasma.


All reagents supplied need to be stored at 2 °C – 8 °C, unopened reagents will retain reactivity until expiration date. Do not use reagents beyond this date.

  • SARS-Co-V-2 NP Coated ELISA Plate.
  • Positive Control.
  • Blank Control.
  • 5x Assay Buffer.
  • 10x Wash Buffer.
  • 100x Detection Antibody Buffer.
  • Substrate Solution.
  • Stop Solution.


Negative Control: 0.198, 0.177 (OD450).
Positive Control: 0.868, 0.827 (OD450).
Serum From Healthy Subjects: 0.207, 0.175, 0.223 (OD450).
Serum From COVID-19 Patients: 0.754, 0.362 (OD450).

Suggested Cut-Off Values: Negative: < 0.25 (450nm). Positive: ≥ 0.25 (450nm).

It is advised that each laboratory establishes its own normal and pathological refence range for detection of anti-NP antibodies.


– Negative Result: Samples absorbance/cut-off < 0.9.
– Positive Result: Samples absorbance/cut-off > 1.1.
– Borderline Result: Samples absorbance/cut-off = 0.9 – 1.1.
– Sensitivity: 93.33%.
– Specificity: 95%.
– Inter Assay Precision: CV% 5.26, 4.95, 6.11.
– Intra Assay Precision: CV% 5.73, 4.51, 6.68.


  1. Monitoring Specific IgM and IgG Production Among Severe COVID-19 Patients Using Qualitative and Quantitative Immunodiagnostic Assays: A Retrospective Cohort Study. Front Immunol. (2021) 12: 705441. Al-Mughales et al.
  2. SARS-CoV-2 enzyme-linked immunosorbent assays as proxies for plaque reduction neutralisation tests. Sci Rep. (2022) 12 (1): 3351. Kay G.A.,et al.
  3. Early Detection of SARS-CoV-2 Seroconversion in Humans with Aggregation-Induced Near-Infrared Emission Nanoparticle-Labeled Lateral Flow Immunoassay. ACS Nano. (2021) 15 (5): 8996-9004. Chen R., et al.
  4. Sensitivity and Specificity of Anti-SARS-CoV-2 Detection Kits – Comparison and Agreement between Fifteen Different Assays. J Infect Dis. (2022) 75 (1): 16-23. Kanani F., et al.


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