Anti-SARS-CoV-2 Neutralization Antibody Test Kit (Colloidal Gold)

The Anti-SARS-CoV-2 Neutralization Antibody Test Kit (Colloidal Gold) is a rapid in vitro chromatographic immunoassay, used for the qualitative detection of neutralization antibodies against SARS-CoV-2 viral spike proteins, in human whole blood, serum or plasma samples. The coronaviruses encode four major structural proteins, the spike (S), membrane (M), envelope (E), and nucleocapsid (N) proteins. The S protein contains a receptor-binding domain (RBD), which is responsible for recognizing and interacting with the cell surface receptor angiotensin-converting enzyme 2 (ACE2). ACE2 is widely expressed in the respiratory tract of the lungs, on the cell surfaces in the alveoli, trachea, and bronchi, as well as on macrophages and other cell types. The ACE2-RBD interaction is essential for SARS-CoV-2 virus particle entry into the host cells, and therefore viral replication and infection. Neutralizing antibodies secreted by B lymphocytes can bind to the RBD, blocking the interaction with ACE2, and granting the host strong immunity against the pathogen.

The test is a qualitative membrane-based immunoassay for the detection of SARS-CoV-2 neutralizing antibodies. The blood sample and a buffer solution are dropped into the sample well, and the solution migrates up the membrane by the capillary effect. If there are neutralizing antibodies in the sample, these bind to colloidal gold-labeled SARS-CoV-2 spike protein (S) contained within the membrane, and these travel up the membrane with the solution. Once the solution reaches the test (T) line, the spike protein subunit RBD-NTD-CTD that is coated to the T area is also bound by the neutralizing antibodies. The coated spike protein-neutralizing antibody-spike protein-colloidal gold complex at the T area becomes visible as a colored line, as the colloidal gold appears red when concentrated. If there are no neutralizing antibodies in the sample, the colloidal gold labelled spike proteins spread over the membrane instead, and no red line appears at the T area.

The solution also contains colloidal-gold labeled chicken IgY, which is captured by mouse anti-chicken IgY antibodies coated to the membrane at the control (C) line. If the C line does not appear after 15 minutes, the result is invalid, and the sample needs to be tested again using a new test cassette, carefully following the instructions. The C line appearing indicates the buffer solution has been applied, proper membrane wicking has occurred, and antibodies are able to bind in the test conditions. The absence of a C line helps to identify false negative test results.