SG Diagnostics

SG Diagnostics Nucleoprotein Antibody Detection Kit

The SG Diagnostics COVID-19 Nucleoprotein Antibody Detection Kit (Colloidal Gold-Based) is intended for the in vitro qualitative detection of antibody that binds the nucleoprotein of SARS-CoV-2 in human serum or plasma. It is is intended for use by medical professionals or trained operators who are proficient in performing rapid lateral flow tests.

Coronaviruses are a large family of viruses which may cause illness in animals or humans. SARS-CoV-2 is an enveloped, single-stranded RNA virus of the β genus. The virus can cause mild to severe respiratory illness and has spread globally. The most common symptoms of COVID-19 include fever, dry cough and tiredness. The incubation period for COVID-19, which is the time between exposure to the virus (becoming infected) and the onset of symptoms, is on average 5-6 days, however can be up to 14 days. 

The window period for COVID-19, which is the time between exposure to the virus (becoming infected) and the appearance of detectable antibodies to the virus can be up to 24 days. The virus encodes 4 main types of structural protein, which includes spike (S) protein, envelope (E) protein, membrane (M) protein and nucleocapsid (N) protein. The nucleoprotein is mainly responsible for RNA replication. It is often being tested for in a coronavirus diagnostic testing tool and it is a core component of rapid immunological diagnostic reagents.

The SG Diagnostics COVID-19 Nucleoprotein Antibody Detection Kit is an immunochromatographic membrane assay that uses nucleoprotein to detect nucleoprotein antibody in sample (human serum or plasma) via the double antibody sandwich method. After loading, the sample will diffuse upwards from the charging end by capillary action, and then the nucleoprotein antibody in the sample will combine with the nucleoprotein in the marker pad to form colloidal gold antibody-antigen complex; the complex continues to diffuse upwards to the nitrocellulose membrane with the sample, and then blocked by Test (T) Line packed with antibody to form colloidal gold labeled antibody-antigen-immune complex. The rest unblocked colloidal gold complex continues to move upwards and combine with Control (C) line (quality control line), indicating that the reaction is completed.

  • The assay time is shorter (within 10 minutes as compared to around 24 hours for enzyme-linked immunosorbent assay (ELISA))
  • The cost is cheaper than ELISA
  • The test can be carried out at the point-of-care
  • It is a one-step assay that requires no special skills or instrumentation to achieve the result(s)
  • It has a long shelf life and assay reagents do not require refrigeration or freezer storage
  • The samples do not need to be pre-treated before applying to the assay

Note: The test cassette must be at room temperature before use, and the test must be operated at room temperature.

  1. Apply 1 drop (~ 20μL) of serum or plasma with the disposable Pasteur pipette that is provided by the kit onto the charging hole of the Test Cassette. 
  2. Apply 3 drops (~ 60μL) of sample eluent onto the charging hole of the Test Cassette. 
  3. Start and timer and read the results after 10 minutes. The result is invalid after 15 minutes.
  4. Dispose the Pipette and Test Cassette in the appropriate biohazard waste.

Note: In a valid, tested device, a red line appears at the Control Line position, confirming that the sample has flowed through the test strip and the reagents are working.

The test results are analyzed as follows:
A negative specimen will give a single red colored Control Line in the top half of the window, indicating a negative result. This Control Line means that the detection part of the test was done correctly, but no COVID-19 Nucleoprotein antibody was detected. 

A positive specimen will give two red colored lines. This means that COVID-19 Nucleoprotein antibody was detected. Specimens with low levels of antibody may give a faint Sample Line. Any visible red colored Sample Line is positive. 

If no lines are seen, if just the red Test Line is seen, or if the red Control Line is not seen, the assay is invalid. Invalid tests should be repeated. 

Coming soon

  • Huang, Chaolin, Yeming Wang, Xingwang Li, Lili Ren, Jianping Zhao, Yi Hu, Li Zhang et al. “Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China.” The lancet 395, no. 10223 (2020): 497-506.
  • Astuti, Indwiani. “Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2): An overview of viral structure and host response.” Diabetes & Metabolic Syndrome: Clinical Research & Reviews 14, no. 4 (2020): 407-412.
  • Jiang, Shibo, Christopher Hillyer, and Lanying Du. “Neutralizing antibodies against SARS-CoV-2 and other human coronaviruses.” Trends in immunology 41, no. 5 (2020): 355-359.
  • World Health Organization (WHO). URL: https://www.who.int/emergencies/diseases/novel-coronavirus-2019. Accessed on 1st December 2020.

Coming soon

Test Kit Specifications Materials Provided

Test Cassettes (10/20/25/30/40/50)
A test cassette consists of test strip, packed individually in a sealed desiccant foil pouch.
Disposable Pasteur Pipettes (10/20/25/30/40/50)
Sample Eluent (1)
Product Insert (1)

Test Kit Characteristics

Assay format
Lateral flow test / immunochromatographic
Testing Time
10 – 15 mins
Type of Analyte
Anti-Nucleocapsid protein IgG antibody that binds the Nucleocapsid protein of SARS-CoV-2
Sample material
Serum or plasma

External Clinical Evaluation

Coming soon

For more information, you can download the file below.