Enzyme-linked immunosorbent assay – ELISA

ELISA (enzyme-linked immunosorbent assay) is one of the most commonly used assays. In 1971, Perlmann and Engvall introduced this assay and explained its basic chemistry. In this technique, we quantify the antibodies, antigens, proteins, enzymes, and peptides. This technique is being used in HIV diagnosis, pregnancy tests, and cytokinesis measurement in serum. ELISA provides a vast range for testing a sample by its 96 separate polystyrene plates, in a single experiment. All of the 96 plates carry NUNC immuno-plates for attachments of antibodies and antigens. It can be used on two divide principles. 1st Wet lab techniques, which are used to identify the analyte from a liquid sample. 2nd Dry lab techniques, in this the last step of detection of analyte (Specific antigen or antibody) is “dry step” meaning provides reading on a dry stirp.

ELISA has 4 types on the base of its modifications and requirements.

Types of ELISA

1. Direct ELISA is a single-stage process, with a single antibody meaning that no second antibody is required during the whole process. This particular antibody attaches to its substrate (Antigen) and produces a detectable signal, and the antigen is identified. 
2. In Reverse ELISA two antibodies are used (primary unlabeled and secondary labeled antibody). In the first step, the primary antibody attaches to its substrate (Antigen) then secondary enzyme-linked antibody attaches to the primary antibody and produces a signal.
3. Sandwich (Collection of direct and indirect ELISA). Here an immobilized unlabeled primary antibody is used, which serves the purpose of capturing the required antigen. Then the secondary labeled antibody attaches and produces a signal for detection.
4. Competitive (inhibition ELISA). In this type unlabeled antibody binds to the target antigen and forms a complex (Ag-An). This complex is then placed in a inhibit antigen-coated plate. Now the second enzyme-labeled antibodies are introduced in the process and attaches to the target antigen and produce a detectable signal.

Oldest Neutralization Testing Techniques

Before this ELISA, Radioimmunoassay was the only method present to detect the required antibodies or antigens. It was the first time explained by R. S. Yalow and S. Berson during endogenous plasma insulin testing, in 1960. This assay is very helpful in identifying a very small quantity of antibodies or antigens in the serum. Instead of enzymes, radioisotopes are used for identifications. The limited and labeled antigens bounded with their specific antibodies are used against the unlabeled antibodies and antigens in the serum. During incubation, the number of labeled and unlabeled antigens remains directly proportional and attach to the active sites of labeled antibodies. In the end theses, unlabeled antigens are separated by using the gamma encounter. Though this an old technique, it is still very useful and widely used. If you are looking for the best COVID-19 neutralizing antibody test kit, here is what you are looking for. It is also available in lateral flow assays (a paper assay, with sample available in the device).