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An Introduction to ELISA

The enzyme-linked immunosorbent assay, also known by the acronym, ELISA, was created in the 1970s. This common lab test measures the concentration of an analyte, which is generally antibodies or antigens in a particular solution. With ELISA, quantitative results can be detected, which sets it apart from other similar type tests.

The basic procedure for ELISA begins with a coating step. In this step, a polystyrene plate is covered with a solution that has either antibodies or antigens. The liquid is then dumped and the plate is washed. Next, is the blocking step. In this step, a solution that is protein-based and unrelated to the first solution covers the unbound sites on the plate. Once again, the liquid is removed and the plate is washed off. In the detection step, the enzyme-conjugated antigen or antibody binds to the target antigen or antibody. The plate is then drained and washed again. Finally, a substrate is placed in the plate and the signal given by the reaction of the enzyme and substrate is what is measured.

Typical components of an ELISA Kit
• Typical components of an ELISA Kit

There are four different types of ELISA tests:
• Direct: This method is the fastest and has fewer steps. It is also less prone to an error.
• Indirect: This method has increased sensitivity and it costs less as fewer labeled antibodies are required.
• Sandwich ELISA: With this method, there are more steps involved. However, the results are highly specific.
• Competition or Inhibition ELISA: This method is usually used when only one antibody is available or when the analyte is small.

In addition to these different methods to perform ELISA, there are also different detection methods; direct and indirect.

The results of an ELISA test can be quantitative, qualitative, or semi-quantitative. Results are usually graphed to compare it with other results and come to a definitive result. Quantitative results are read in comparison to a standard curve. Qualitative results simply give a yes or a no as to whether or not an antigen is present. Semi-quantitative results are compared in relative levels.

This test is one of the most sensitive immunoassay tests available today. The sensitivity will depend upon the characteristics of the antibody-antigen reaction. To improve the results, the lab can add a substrate, such as those that give an enhanced chemiluminescent or fluorescent signal.
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- Introduction - Section 1 ↣ Section 2
rightarrow An Introduction to ELISA
    - Brief introduction to basic procedures, different types of ELISA tests...
rightarrow Overview Of The Basic ELISA Procedure
    - ELISA procedures, features, benefits, improvements...
rightarrow Understanding The ELISA Assay Types
    - ELISA's advantages, Direct, Sandwich, Competitive ELISA...
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Section 3 Section 4 Section 5
rightarrow Defining ELISA Detection Options
    - The two ELISA detection options: Direct and Indirect...
rightarrow ELISA Results
    - Testing Data: Quantitative, Qualitative, Semi-quantitative...
rightarrow Information On ELISA And ELISA Sensitivity
    - ELISA: The most sensitive immunoassays available...

  • enzyme linked immunosorbent assay
  • elisa
  • antibodies
  • MyBioSource
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