Human SARS-CoV-2 S1 RBD IgG Antibody ELISA Kit

Code CSB-EL33241HU
Size 96T,5×96T,10×96T
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Trial Size 24T ELISA Kit Trial Size (Only USD$150/ kit)
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Product Details

Alternative Names
S; 2; Spike glycoprotein; S glycoprotein; E2; Peplomer protein)
Uniprot No.
Homo sapiens (Human)
Sample Types
serum, plasma
Detection Range
Assay Time
Sample Volume
Detection Wavelength
450 nm
Research Area
Infectious Diseases
Assay Principle

The measurement of this assay is based on the indirect ELISA principle, in which the immune complex pre-coated antigen/S1 RBD IgG antibody/HRP-conjugated IgG is formed and then develops color reaction after the addition of TMB substrate solution. The color intensity is directly proportional to the amount of SARS-CoV-2 S1 RBD IgG antibody bound at the initial step. This kit serves as a tool to provide performance data during SARS-CoV-2-related research and development. The OD (optical density) of the sample below 2.1x negative OD was considered negative, and equal or above 2.1x negative OD was positive. It has high throughput with 90 samples at a time (6 wells used for the control) and has been validated with excellent specificity and high precision (less than 15%).
Intra-assay Precision (Precision within an assay): CV%<15%
Three samples of known concentration were tested twenty times on one plate to assess.
Inter-assay Precision (Precision between assays): CV%<15%
Three samples of known concentration were tested in twenty assays to assess.
Typical Data
Test parameter specification test result
Positive control ≥1.0 1.256
Negative control ≤0.25 0.193
Positive rate 20,Positive 100%
Negative rate 20,Negative 100%
Materials provided
    • A 96-well Coated assay plate 1 -- This microplate has been pre-coated with human SARS-CoV-2 S1 RBD antigen.
    • Negative Control (1 x 800 μl) -- It is free of the SARS-CoV-2 S1 RBD IgG antibody and used to preclude the false positive.
    • Positive Control (1 x 800 μl) -- Used to evaluate the validity, stability, and comparability of the test results.
    • HRP-conjugated anti-Human IgG antibody (100 x concentrate) (1 x 120 μl) -- Act as the detection antibody.
    • HRP-conjugate Diluent (1 x 20 ml) -- Dilute the HRPconjugated anti-Human IgG antibody.
    • Sample Diluent (2 x 20 ml) -- Dilute the sample solution.
    • Wash Buffer (25 x concentrate) (1 x 20 ml) -- Wash the unbound regeat.
    • TMB Substrate (1 x 10 ml) -- React with HRP, eliciting a chromogenic color reaction.
    • Stop Solution (1 x 10 ml) -- Stop the color reaction. The solution turns from blue to yellow.
    • Four Adhesive Strips (For 96 wells) -- Seal the microplate when incubation.
    • An Instruction manual
Materials not provided
    • A microplate reader capable of measuring absorbance at 450 nm, with the correction wavelength set at 540 nm or 570 nm.
    • An incubator that can provide stable incubation conditions up to 37°C±5°C.
    • Centrifuge
    • Vortex
    • Squirt bottle, manifold dispenser, or automated microplate washer.
    • Absorbent paper for blotting the microtiter plate.
    • 50-300ul multi-channel micropipette
    • 100ml and 500ml graduated cylinders.
    • Deionized or distilled water.
    • Pipette tips
    • Timer
    • Test tubes for dilution.
and FAQs
Store at 2-8°C. Please refer to protocol.
Lead Time
3-5 working days after you place the order, and it takes another 3-5 days for delivery via DHL or FedEx

The product CSB-EL33241HU is an easy-to-use ELISA Kit intended for the qualitative detection of SARS-CoV-2 S1 RBD IgG antibody in human serum and plasma in vitro. SARS-CoV-2 S1 RBD IgG is an indicator of a recent or prior COVID infection. Infected patients develop IgG against SARS-CoV-2 S1 RBD 7 days post-infection, and IgG content peaks in the third week (IgM was close to vanishing at this time). IgG lasts in the blood for months or even years. After secondary infection, IgG levels in the body of patients increase rapidly and substantially in the short term and remain in the body for a long time, while IgM rarely increases. Serological testing may help to diagnose suspected patients with negative RT–PCR (real-time polymerase chain reaction) results and identify asymptomatic infections.

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What is the differences between the SARS-CoV-2 S protein and N protein?


Spike glycoprotein (S) is a structural protein that protrudes from the lipid envelop to form a typical bulbous, crown-like halo surrounding the viral particle. The S protein of SARS-CoV-2 functions to recognize the receptor, attach to and fuse with the host cell membrane during viral infection. Proteolysis by TMPRSS2 and cathepsin B/L exerts a vital role in priming SARS-CoV-2 S for entry. The S protein consists of two subunits: S1 (bulbous head region) and S2 (stalk region). The receptor-binding domain (RBD) within the S1 subunit is responsible for the recognition and binding to the host receptor ACE2. The S2 subunit is composed of fusion peptide (FP), heptapeptide repeat sequence 1 (HR1), HR2, transmembrane (TM) domain, and cytoplasmic domain fusion (CT), and is involved in the virus-cell fusion and viral entry. As the main antigen component of the SARS-CoV-2, S protein-targeted neutralizing antibodies (nAbs) can induce protective immunity against viral infection.

Nucleocapsid (N) phosphoprotein, a structural protein of SARS-CoV-2, binds to the viral RNA, a process known as RNA encapsidation, forming the nucleocapsid. The N protein of SARS-CoV-2 comprises an N-terminal domain (NTD) that captures the viral RNA genome and a C-terminal domain (CTD) that anchors the ribonucleoprotein complex to the membrane by interacting with the viral membrane (M) protein during viral assembly. As a multifunctional molecule, the N protein not only participates in the process of RNA synthesis and folding but also affects host cellular responses to viral infection, including cell cycle and translation. It also contributes to viral transcription efficiency and pathogenesis.


What is the difference between IgG and IgM?


Immunoglobulin G (IgG): It is the most common and abundant antibody in the body, accounting for about 70-80% of the total human immunoglobulins. IgG is generated in most patients within 7-10 days after symptoms develop and peaks in the third week and then declines to a lesser content level. It can be rapidly and substantially reproduced after a second exposure to the same antigen. A positive IgG test result indicates that the patient is in convalescence or prior infection. IgG test can be used for the course monitoring and retrospective diagnosis of patients (eg. COVID-19). IgG is largely responsible for long-term immunity after infection or vaccination. Unique among the immunoglobulins, IgG can pass through the placenta. IgG antibodies from the mother protect the fetus during the pregnancy and to the baby during its first few months of life. IgG is subdivided into four subclasses: IgG1, IgG2, IgG3, and IgG4.

Immunoglobulin M (IgM): It is the first antibody produced in response to new infection or a new "non-self" antigen, providing short-term protection. IgM increases for several weeks and peaks in the second week and then declines as IgG synthesis begins. The positive blood test of IgM can be an indicator of early infection. Serological tests for IgM therefore can be used for the early screening of suspected cases.


What is the assay procedure?


1. Prepare all reagents and samples as instructed.
2. Refer to the Assay Layout Sheet to calculate the number of the wells (including a blank well) to be used and put the remaining wells and the desiccant back into the pouch to seal and store at 4 °C.
3. Add 100 µl positive control, negative control, or sample (may require dilution) to each well. Seal and incubate 30 minutes at  37°C.
4. After thorough washing, add 100 μl HRP-conjugated Anti-Human IgG Antibody into each well (not to the blank well). Seal and incubate 30 minutes at  37 °C.
5. Wash the unbound reagent and add 90 µl TMB Substrate Solution to each well. Incubate for 20 minutes at 37°C.
6. Add 50 µl Stop Solution to each well and gently tap the plate to ensure thorough mixing. Take the blank well as zero and read the at 450 nm within 10 minutes using a microplate reader.

Target Background

(From Uniprot)
attaches the virion to the cell membrane by interacting with host receptor, initiating the infection. Binding to human ACE2 receptor and internalization of the virus into the endosomes of the host cell induces conformational changes in the Spike glycoprotein. Binding to host NRP1 and NRP2 via C-terminal polybasic sequence enhances virion entry into host cell. This interaction may explain virus tropism of human olfactory epithelium cells, which express high level of NRP1 and NRP2 but low level of ACE2. The stalk domain of S contains three hinges, giving the head unexpected orientational freedom. Uses human TMPRSS2 for priming in human lung cells which is an essential step for viral entry. Can be alternatively processed by host furin. Proteolysis by cathepsin CTSL may unmask the fusion peptide of S2 and activate membranes fusion within endosomes.; mediates fusion of the virion and cellular membranes by acting as a class I viral fusion protein. Under the current model, the protein has at least three conformational states: pre-fusion native state, pre-hairpin intermediate state, and post-fusion hairpin state. During viral and target cell membrane fusion, the coiled coil regions (heptad repeats) assume a trimer-of-hairpins structure, positioning the fusion peptide in close proximity to the C-terminal region of the ectodomain. The formation of this structure appears to drive apposition and subsequent fusion of viral and target cell membranes.; Acts as a viral fusion peptide which is unmasked following S2 cleavage occurring upon virus endocytosis.; May down-regulate host tetherin (BST2) by lysosomal degradation, thereby counteracting its antiviral activity.
Gene References into Functions
  1. Study presents crystal structure of C-terminal domain of SARS-CoV-2 (SARS-CoV-2-CTD) spike S protein in complex with human ACE2 (hACE2); hACE2-binding mode similar overall to that observed for SARS-CoV. However, details at the binding interface show that key residue substitutions in SARS-CoV-2-CTD slightly strengthen the interaction and lead to higher affinity for receptor binding than SARS-CoV receptor-binding domain. PMID: 32378705
  2. crystal structure of the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2 bound to the cell receptor ACE2 PMID: 32365751
  3. crystal structure of the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2 (engineered to facilitate crystallization) in complex with ACE2 PMID: 32320687
  4. Out of the two isolates from India compared to the isolates from Wuhan, China, one was found to harbor a mutation in its receptor-binding domain (RBD) at position 407 where, arginine was replaced by isoleucine. This mutation has been seen to change the secondary structure of the protein at that region and this can potentially alter receptor binding of the virus. PMID: 32275855
  5. Structural modeling of the SARS-CoV-2 spike glycoprotein show similar receptor utilization between SARS-CoV-2 and SARS-CoV, despite a relatively low amino acid similarity in the receptor binding module. Compared to SARS-CoV and all other coronaviruses in Betacoronavirus lineage B, an extended structural loop containing basic amino acids were identified at the interface of the receptor binding (S1) and fusion (S2) domains. PMID: 32245784
  6. crystal structure of CR3022, a neutralizing antibody from a SARS patient, in complex with the receptor-binding domain of the SARS-CoV-2 spike (S) protein to 3.1 A; study provides insight into how SARS-CoV-2 can be targeted by the humoral immune response and revealed a conserved, but cryptic epitope shared between SARS-CoV-2 and SARS-CoV PMID: 32225176
  7. SARS-CoV and SARS-CoV-2 spike proteins have comparable binding affinities achieved by balancing energetics and dynamics. The SARS-CoV-2-ACE2 complex contains a higher number of contacts, a larger interface area, and decreased interface residue fluctuations relative to the SARS-CoV-ACE2 complex. PMID: 32225175
  8. Interaction interface between cat/dog/pangolin/Chinese hamster ACE2 and SARS-CoV/SARS-CoV-2 S protein was simulated through homology modeling. Authors identified that N82 of ACE2 showed closer contact with receptor-binding domain of S protein than human ACE2. PMID: 32221306
  9. SARS-CoV-2 S glycoprotein harbors a furin cleavage site at the boundary between the S1/S2 subunits, which is processed during biogenesis and sets this virus apart from SARS-CoV and SARS-related CoVs; determined cryo-EM structures of the SARS-CoV-2 S ectodomain trimer. PMID: 32201080
  10. Study demonstrates that SARS-CoV-2 uses the SARS-CoV receptor ACE2 for entry and the serine protease TMPRSS2 for S protein priming. PMID: 32155444
  11. The ACE2-B0AT1 complex exists as a dimer of heterodimers. Structural alignment of the RBD-ACE2-B0AT1 ternary complex with the S protein of SARS-CoV-2 suggests that two S protein trimers can simultaneously bind to an ACE2 homodimer. PMID: 32142651
  12. study demonstrated SARS-CoV-2 S protein entry on 293/hACE2 cells is mainly mediated through endocytosis, and PIKfyve, TPC2 and cathepsin L are critical for virus entry; found that SARS-CoV-2 S protein could trigger syncytia in 293/hACE2 cells independent of exogenous protease; there was limited cross-neutralization activity between convalescent sera from SARS and COVID-19 patients PMID: 32132184
  13. study determined a 3.5-angstrom-resolution cryo-electron microscopy structure of the 2019-nCoV S trimer in the prefusion conformation; provided biophysical and structural evidence that the 2019-nCoV S protein binds angiotensin-converting enzyme 2 (ACE2) with higher affinity than does severe acute respiratory syndrome (SARS)-CoV S PMID: 32075877

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Subcellular Location
Virion membrane; Single-pass type I membrane protein. Host endoplasmic reticulum-Golgi intermediate compartment membrane; Single-pass type I membrane protein. Host cell membrane; Single-pass type I membrane protein.
Protein Families
Betacoronaviruses spike protein family
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