Full Name: SARS-CoV-2 S1RBD IgM ELISA Kit
Reactivity: Human
Sample Type: Serum, Plasma
Sensitivity: Qualitative


SARS-CoV-2 is composed from four different structural proteins: spike (S), E envelope (E), nucleocapsid protein (NP) and membrane (M). The spike protein can be cleaved to form a S1 sub-unit that is the approx. 700 amino acids N-terminal and the S2 sub-unit which is approx. 600 amino acids C-terminal. The S1 is important for viral attachment whereas the S2 is vital for membrane fusion. There are two structural proteins found in the genome of SARS-CoV-2: spike (S) and E envelope (E). The S protein has a molecular weight of approx. 125,000 daltons and is composed from three different structural subunits: the N-terminal A1, A2, and C1; the middle B1; and the C-terminal D1. The N-terminal A2 is important for viral fusion. The E protein has a molecular weight of approx. 22 kDa with an N terminus which can be anchored either to the membrane or N terminus of the S protein.

The nucleocapsid shell contains a negative-strand RNA genome capped by an external phospholipid membrane, with a hydrophobic “head” and a hydrophilic “tail” which are connected through the viral envelope. The head is lined with spikes called glycoprotein spikes. Entry into cells occurs via fusion with either host cell membranes or endosomal membranes. The spike glycoprotein present on the viral surface binds to specific receptors on the target cell plasma membrane and fuses it with the viral membrane, forming a tube through which the nucleocapsid enters the host cell.

Within the S1 sub-unit there is a receptor binding domain (RBD), this plays a critical role in binding the extracellular peptidase domain of SARS-CoV-2 to the cell surface. There are two binding domains within the S1 sub-unit, the receptor binding domain (RBD) and a transmembrane protein, previously referred to as membrane binding domain. The RBD is characterized by a core of hydrophobic amino acids surrounded by basic residues that bind to various cell surface receptors such as neutralizing antibodies or ligand molecules. The membrane binding domain is estimated to be approximately 25 kDa in size and have a hydrophilic core with eight conserved serine/threonine residues that form six sulfido-arginine repeats.


Human SARS-CoV-2 S1RBD IgM ELISA kit is intended for analysing IgM class antibodies in anti-SARS-CoV-2 spike protein S1 receptor-domain (S1RBD) using human samples of plasma and serum.


Each kit contains the following components and is sufficient for 96 tests.

  • One Aluminium Pouch: Containing microwell plate bound with SARS-CoV-2 S1RBD protein.
  • 10x Wash Buffer.
  • 5x Assay Buffer.
  • 100x Detection Antibody Solution: HRP coated anti IgM monoclonal antibody.
  • 10x Standard.
  • Substrate Solution.
  • Stop Solution.


Serum From Healthy Subjects: 0.404, 0.965, 0.675, 0.358, 1.148, 1.353, 0.293, 0.88, 1.591, 3.814 (OD450).
Serum From COVID-19 Patients: 0.116, 0.203, 0.148, 0.102, 0.072, 0.155, 0.08, 0.197, 0.064, 0.092 (OD450).

It is advised that each laboratory establishes its own normal and pathological refence range for detection of anti-S1RBD IgM antibodies.


– Inter Assay Precision: CV = Less than 10%.
– Intra Assay Precision: CV = Less than 8%.


  1. Anti-spike S1 receptor-binding domain antibodies against SARS-CoV-2 persist several months after infection regardless of disease severity. J Med Virol. (2021) 93 (5): 3158-3164. Bavaro D.F., et al.
  2. Serology Testing Demonstrates That Antibodies to SARS-CoV-2 S1-RBD Correlate with Neutralization of Virus Infection of Vero E6 Cells. J Appl Lab Med. (2021) 6 (5): 1386-1389. Freeman J., et al.
  3. Antibody signature induced by SARS-CoV-2 spike protein immunogens in rabbits. Sci Transl Med. (2020) 12 (550): eabc3539. Ravichandran S., et al.
  4. Antigenic Cross-Reactivity Between SARS-CoV-2 S1-RBD and Its Receptor ACE2. Front Immunol. (2022) 13: 868724. Lai Y.C., et al.


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