ELISA Purpose And Procedure

ELISA is something that we are all starting to hear more about, and now we are looking forward to a future where ELISA is capable of more, and ELISA kits are becoming more developed, available and useful. 

But, to those who are new to the concept of ELISA, it is important to understand the purpose and procedure of ELISA overall. Let’s open up a greater understanding of ELISA tests to you.

What Is ELISA?

ELISA is a basic assay technique. It is a form of testing using enzyme-linked immunosorbent assays. It is done to detect and measure hormones, peptides, antibodies, and the proteins in our blood. 

Antibodies, specifically, are blood proteins which are made by our bodies in response to a specific type of antigen entering our bodies. It helps to do this to examine the presence of antibodies in someone’s body in the case of detecting infectious diseases. 

ELISA is a very distinguished analysis in comparison to other antibody-assays. It takes out rather quantitative results and the separation of non-specific and specific interactions which can occur in the serial binding to a solid surface, which is typically a polystyrene multiwell plate.

Types Of ELISA Tests

There are several types of ELISA tests. Direct, indirect, sandwich, and competitive, we will look into each of these before we explore more. 

Direct ELISA testing. 

  • A specific labeled primary antibody will bind to a specific target.

Indirect ELISA testing.

  • This is the most common. 
  • Said target will be bound by the primary antibody, and it will then be detected when a secondary labeled antibody binds to the primary one. 
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Sandwich ELISA testing. 

  • This technique is used to detect sample antigens. 
  • The target will be absorbed into the assay plate, and then it will be bound by 2 primary antibodies after. 

Competitive ELISA testing. 

  • This is often used for much smaller targets, which may possibly only have a single binding site. 
  • Detection is made via competitive binding. 

Principle Of ELISA

ELISA testing works on the simple principle that some specific antibodies will bind the targeted antigen, and thus detect the presence and amount of antigens which are binding. 

To be able to increase the sensitivity and preciseness of the specific assay, the plate will need to be properly coated with antibodies that have a high affinity. 

ELISA is able to provide a useful measurement of antigen to antibody concentrations. 

Procedure Of ELISA 

So, how does all this work? It sounds a bit complex right? It really is not. All you need to know is that ELISA is one of the best ways of testing, and it is used a massive amount in testing today. 

Blood tests are a type of ELISA test in a way. But, let us explain it for you in a little more detail. 

ELISA tests are one of the easiest and most efficient blood tests that can be done in the medical field. It is extremely quick and rapid, and all it needs is a blood sample from the specific patient

Let’s look at the entire procedure with ELISA testing…

  1. Firstly, an antibody will be attached to a polystyrene plate, as a solid surface, and will then be attracted to, or even have an affinity to bacteria, hormones, or other antibodies. 
  2. Then, a microtiter that is coated with antigens is filled with this created antigen-antibody mix, after these antibodies will then be removed by washing. 
  3. Next, a second antibody which is specific to the primary antibody will be added in, usually conjugated with an enzyme. 
  4. Then free enzyme-linked secondary antibodies will be removed by washing this plate. 
  5. Then, finally, the substrate will be added in. This substrate will be converted by the aforementioned enzyme to form a colored product. This can then be measured by spectrophotometry. 
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HCG proteins which will indicate pregnancy are also indicated by an ELISA test. So, yes, pregnancy tests are technically ELISA tests in a sense. Or at least the ones that use a combination of blood or urine sample, as well as purified HCG which is linked to an enzyme, which then gets added into the system. 

If HCG is not present in the specific testing sample, then only the specially linked enzyme will bind to the solid surface. 

Therefore, the more of the interesting substance is present, the more of a reaction will occur, and less of a linked enzyme will bind to the specified solid surface. 

These reactions will often be indicated with a change of color inside the solution. I.e. pregnancy tests, ovulation tests… These are common ones.

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