1. ELISA

2. What is ELISA?
ELISA is an abbreviation for "enzyme-linked immunosorbent assay.“
The Enzyme-Linked Immunosorbent Assay (ELISA) is a technique used to detect antibodies or infectious agents in a sample.

3. The ELISA test involves:
an enzyme (a protein that catalyzes a biochemical reaction).
It also involves an antibody or antigen (immunologic molecules).

4. What is the use of an ELISA test?
ELISA tests are widely utilized to detect substances that have antigenic properties, primarily proteins. The substances detected by ELISA tests include hormones, bacterial antigens and antibodies

5. How does an ELISA test work?
The most basic type consists of an antibody attached to a solid surface.
This antibody has affinity for (will latch on to) the substance of interest.

6. It uses an enzyme linked to an antibody or antigen as a marker for the detection of a specific protein, especially an antigen or antibody.
It is often used as a diagnostic test to determine exposure to a particular infectious agent, such as the AIDS virus, by identifying antibodies present in a blood sample

7. Procedure
A plate is coated with a primary antibody, which recognizes the antigen of the target molecule and bonds with it.
The antigen-antibody complex is recognized by a secondary antibody that is joined to an enzyme that catalyzes the reaction mixture, yielding a specific color.
Positive reaction is detected by the marker changing color when an appropriate substrate is added

8. By measuring the optical density of this color, the presence and number of a specific molecule can be determined; the density of color is proportional to the advancement of the reaction or disease being tested
If there are no antigen in the sample, the second antibody will not be able to stick and there will be no color change ( no reaction)

10. i: test serum is incubated with antigen immobilized on a 96-well plate or
ii: Secondary antibodies labeled with an enzyme are added
iii: After washing, any bound secondary antibodies can be detected using the marker. The label used is an enzyme which induces a colour change when the substrate is added.

12. What are the advantages of ELISA?
ELISA tests are generally relatively accurate tests.
They are considered highly sensitive and specific.
They have the added advantages of not needing radioisotopes (radioactive substances) or a costly radiation counter (a radiation-counting apparatus).