ELISA, short for Enzyme-Linked Immunosorbent Assay, is a very sophisticated method for detecting various targets. One of the advantages of ELISA is that it is fast and easy to perform, therefore it is widely used for both diagnostic and research purposes.

As the name suggests, ELISA involves the use of enzymes and the specific binding of antibodies and antigens. You can also get the Amyloid Beta/APP ELISA from various online sources. Depending on how it works, ELISA can be divided into four main types: direct, indirect, sandwich, and competitive. Let's look at them one by one.

Direct ELISA

Direct ELISA uses only one enzyme-labeled primary antibody, which means that a secondary antibody is not required. The enzyme-labeled primary antibody binds "directly" to the target (antigen), which is immobilized on the plate (hard surface).

The enzyme bound to the primary antibody then reacts with its substrate to produce a visible signal that can be measured. In this way, the desired antigen is detected.

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Indirect ELISA

Both primary and secondary antibodies are used in indirect ELISA. However, in this case, the primary antibody is not labeled with the enzyme. In contrast, secondary antibodies are labeled with enzymes.

The primary antibody binds to the immobilized platelet antigen, and then the enzyme-labeled secondary antibody binds to the primary antibody.

ELISA sandwich

In direct and indirect ELISA, the antigen is immobilized on the plaque. However, in sandwich ELISA, the antibodies are immobilized on the plate and these antibodies are called capture antibodies.

In addition to the capture antibody, sandwich ELISA also includes the use of detection antibodies, which typically include an unlabeled primary detection antibody and an enzyme-labeled secondary detection antibody.

Competitive ELISA

Compared to the three types of ELISA above, competitive ELISA is relatively complex because it involves the use of inhibitory antigens, so competitive ELISA is also known as inhibitory ELISA.

In fact, any of the three formats, direct, indirect, and sandwich, can be adapted to the racing format. In competitive ELISA, the inhibitory antigen and the desired antigen compete for binding to the primary antibody.