what are the types of ELISA methods?

Answer 1

The Enzyme-Linked Immuno-Sorbent Assay, or ELISA, is a biochemical technique used mainly in immunology to detect the presence of an antibody or an antigen in a sample.
It is a useful tool both for determining serum antibody concentrations (such as with the Human Immunodeficiency Virus, HIV test or West Nile Virus) and also for detecting the presence of antigen.
For full details about its types, please refer to :
http://en.wikipedia.org/wiki/ELISA

Answer 2

Enzyme-linked immunosorbent assays (ELISAs) can be used to measure almost any protein, including hormones. This test combines the specificity of antibodies with the sensitivity of simple enzyme assays. Figure 74-10 shows the basic elements of this method, which is often performed on plastic plates that each have 96 small wells. Each well is coated with an antibody (AB1) that is specific for the hormone being assayed. Samples or standards are added to each of the wells, followed by a second antibody (AB2) that is also specific for the hormone but binds to a different site of the hormone molecule. A third antibody (AB3) is added that recognizes AB2 and is coupled to an enzyme that converts a suitable substrate to a product that can be easily detected by colorimetric or fluorescent optical methods.
Because each molecule of enzyme catalyzes the formation of many thousands of product molecules, even very small amounts of hormone molecules can be detected. In contrast to competitive radioimmunoassay methods, ELISA methods use excess antibodies so that all hormone molecules are captured in antibody-hormone complexes. Therefore, the amount of hormone present in the sample or in the standard is proportional to the amount of product formed.
The ELISA method has become widely used in clinical laboratories because (1) it does not employ radioactive isotopes, (2) much of the assay can be automated using 96-well plates, and (3) it has proved to be a cost-effective and accurate method for assessing hormone levels.

Answer 3

sandwich ELISA and competitive ELISA

Answer 4

two main types: direct and indirect
for various purposes, indirect has a few variations.