Question

Which of the following types of ELISA contain the following steps? Antigen binding, Blocking, Primary antibody. An enzyme-linked antibody, substrate, colorimetric reading (Represented in the diagram).

(A)Direct ELISA
(B)Indirect ELISA
(C)Competitive ELISA
(D)Sandwich ELISA

Answer 1

Hint: It can be seen that the sample is present in between and antibodies are present on both sides of the samples. This type of ELISA is very efficient in sample antigen detection.

Complete answer:
A Sandwich ELISA measures the concentration of antigen between two layers of the antibody. The vessel is first coated with a primary antibody, then with the sample in which antigen is to be detected and then coated with a detecting antibody. After that enzyme-linked secondary antibody is added which binds to the detecting antibody. Now substrate is added which is converted to detectable form with the help of an enzyme.

Additional Information: In sandwich ELISA, it quantifies antigens between two layers of antibodies. The antigen which is to be measured must contain at least two antigenic epitopes capable of binding to antibody because a minimum of two antibodies functions in the sandwich model. Monoclonal or polyclonal antibodies can be either used as the capture and detection antibodies in the Sandwich ELISA model. Monoclonal antibodies are used to detect a single epitope which allows fine detection and quantification of small differences in antigen. A polyclonal antibody is often used as the capture. The advantage of Sandwich ELISA is that the sample which is to be used does not have to be purified before analysis, and the assay can be very sensitive.
So, the correct answer is ‘Sandwich ELISA’

Note: ELISA ( Enzyme-Linked Immunosorbent Assay ) is used to detect the antigen concentration in an unknown sample. It is used for the diagnosis of HIV infection, pregnancy tests, rotavirus, and many more diseases.