ELISA: Enzyme Linked Immuno Sorbent AssayFrom pregnancy detection kits to HIV diagnosis it is ELISA

ELISA: Enzyme Linked Immuno Sorbent Assay

From pregnancy detection kits to HIV diagnosis it is ELISA which gives us appropriate results.  

Though ELISA has got a complex name, the way in which it diagnosis is really simple!

ELISA is performed in special micro titre plates which has wells in which we add our sample and then perform ELISA.

There are 4 types of ELISA:

- Direct

- Indirect

- Sandwich

- Competitive

Direct ELISA is performed by attaching the sample antigens on a surface (walls of wells) then a specific antibody is applied so that it can bind to its corresponding antigen.

The antibodies used in ELISA are special they are known as Detection antibodies. These antibodies have an enzyme linked on its surface. The detection antibody being specific for a particular antigen it will bind only if that particular antigen is present in the sample. After applying antibodies the next step is to wash off the unbound antibodies.

Now, there are 2 possibilities

1. The sample is positive for a particular antigen: In this case it will have detection antibodies bound to it. The sample is then treated with the substrate of enzyme linked to the detection antibody. The enzyme converts the substrate into a product which will give a colour change.

Now this colour change is directly proportional to the amount of antigen present in the given sample.

2. The sample is negative for a particular antigen: In this case, all the detection antibodies will be washed off as the specific antigen is absent. The enzyme bound to the detection antibody will also be lost. Hence, when substrate is added it will not be converted into product giving us no colour change.

This is how ELISA works!

I’ll explain indirect and sandwich ELISA in my next blog. So stay tuned! :)

The image was hand-drawn and submitted to us by Komal M Kadam. You can submit your notes too by mailing it to us at [email protected]