Introduction

ELISA is based on the binding of an antigen (or hapten) to a specific antibody, followed by detection of the bound complex using a second, “detection” antibody that is linked to an enzyme. The enzyme catalyzes a chemical reaction that produces a measurable signal, such as a color change, which can be quantified. There are various different types of ELISA which we will discuss in this study note.

Types of ELISA

There are several different types of ELISA, including:

Direct ELISA

• In this method, the antigen is directly coated onto the plate and the sample is added.
• The sample is added to the plate and allowed to bind to the antigen that is coated on the plate.
• The detection antibody is then added to the plate and binds to the antigen-antibody complex.
• The bound detection antibody is then detected using an enzyme-linked secondary antibody.
• This type of ELISA is useful for detecting antigens that are not easily captured by an antibody.
• It is less sensitive than the sandwich ELISA, but is still widely used.

Indirect ELISA

• In this method, the sample is added to the plate first and the antigen is then detected using a labeled (usually biotinylated) detection antibody.
• The sample is added to the plate and allowed to bind to the antigen if present.
• The primary antibody is then added to the plate and binds to the antigen.
• The detection antibody is then added to the plate and binds to the primary antibody.
• This type of ELISA is useful for detecting antibodies in a sample, such as in serological assays for infectious diseases.
• It is less sensitive than the sandwich ELISA, but is still widely used.

Sandwich ELISA

• In this method, the antigen is captured between two antibodies, one that is coated onto the plate and one that is used as the detection antibody.
• The sample is added to the plate and the antigen binds to the primary antibody that is coated on the plate.
• The detection antibody is then added to the plate and binds to the antigen, forming a sandwich complex.
• The bound detection antibody is then detected using an enzyme-linked secondary antibody.
• This is the most sensitive and specific type of ELISA, making it useful for quantifying low levels of antigen or antibody in a sample.
• It is more complex and takes more time than the direct and indirect ELISA.