Direct ELISA

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.

Direct ELISA

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.

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 direct ELISA works!

Written by Komal Kadam
Illustration by Immense Immunology Insight