The main difference between competitive and noncompetitive ELISA is that competitive ELISA determines the analyte unbound sites, whereas noncompetitive ELISA determines analyte-bound sites.
Competitive and noncompetitive ELISA are two ELISA types that determine the reaction between the analyte and the excess amount of antibodies.
Key Areas Covered
1. What is Competitive ELISA
– Definition, Importance, Procedure
2. What is Non-Competitive ELISA
– Definition, Importance, Procedure
3. Similarities Competitive and Non-Competitive ELISA
– Outline of Common Features
4. Difference Between Competitive and Non-Competitive ELISA
– Comparison of Key Differences
Key Terms
Competitive ELISA, Noncompetitive ELISA
What is Competitive ELISA
Competitive ELISA is a type of ELISA that measures the analyte unbound sites. In competitive ELISA, the antigen in the sample competes with the antigen conjugated to a reporter enzyme for limited antibody binding sites. It uses a single antibody to detect a low molecular weight antigen. The molecular weight of the antigen should be less than 10,000 Daltons. Also, when the antigen content is high in the sample, it results in binding a greater amount of unlabeled antigens than the conjugated antigens during incubation. It produces color when the chromogenic substance is added to the sample. However, samples with high antigen content develop less color leading to a lower signal than those with lower antigen content. Therefore, competitive ELISA generates an inverse relationship between antigen concentration and substrate turnover.
Figure 1: Competitive ELISA
Furthermore, competitive ELISA is a method for detecting low molecular weight antigens with a smaller number of epitopes or antibody-binding sites. Therefore, small molecules, such as peptides and steroids, are suitable for competitive ELISA. Further, it measures the analyte-unbound sites. Also, it is a less sensitive ELISA type. However, it does not use excess antibodies. It has less precision and a narrower working range.
What is Noncompetitive ELISA
Noncompetitive ELISA is a type of ELISA that measures analyte-bound sites. Significantly, it is an immunometric assay or a type of sandwich ELISA which uses two antibodies to detect the antigen. Also, it has two types single antibody immunometric assay and two-site immunometric assay. The common feature of these assays is excess antibodies to detect the analyte. In addition to that, noncompetitive immunoassays are more sensitive in comparison to competitive immunoassays. There, antigen-specific antibodies are often directly labeled with a signal-generating group to measure the concentration of the antigen.
Figure 2: Sandwich ELISA
Additional advantages of the non-competitive ELISA include high precision and a wider working range.
Similarities Between Competitive and Noncompetitive ELISA
- Competitive and noncompetitive ELISA are two types of ELISA.
- They determine the reaction between the analyte and the excess amount of antibodies.
Difference Between Competitive and Noncompetitive ELISA
Definition
Competitive ELISA refers to an ELISA that can measure the concentration of an analyte through its interference in the ELISA assay signal. In contrast, non-competitive ELISA refers to an assay that measures the analyte-bound sites.
Sensitivity
Competitive ELISA is less sensitive, while non-competitive ELISA is more sensitive.
Measurement
Competitive ELISA measures the analyte-unbound sites, while noncompetitive ELISA measures the analyte-bound sites.
Excess Antibody
Competitive ELISA does not use excess antibodies, while non-competitive ELISA uses excess antibodies.
Signal Generating Group
The signal-generating group of competitive ELISA is another antigen, while the signal-generating group of noncompetitive ELISA is an antibody.
Precision and Working Range
Competitive ELISA has less precision and a narrower working range, while non-competitive ELISA has high precision and a wider working range.
Conclusion
In brief, competitive and noncompetitive ELISA are two ELISA types that determine the reaction between the analyte and the excess amount of antibodies. Competitive ELISA is less sensitive and measures the analyte-unbound sites. It does not use excess antibodies. Also, it has less precision and a narrower working range. In comparison, noncompetitive ELISA is more sensitive and measures the analyte-bound sites. However, it uses excess antibodies and has a high precision and wider working range. Therefore, the main difference between competitive and noncompetitive ELISA is their measurement.
References:
- TechNote: What are the differences between ELISA assay types?. Enzo Life Sciences. (2021, May 31).
- Noncompetitive immunoassays for small molecules with high sensitivity and specificity. Advances in Clinical Chemistry.
Image Courtesy:
- “ELISA types” By Allan.richard5093 – Own work (CC-BY SA 4.0) via Commons Wikimedia
- “Sandwich ELISA” By Cawang – Own Work (CC0) via Commons Wikimedia
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