Enzyme Linked Immunosorbent Assay: A Powerful Tool for Biomedical Research and Diagnostics

 

Enzyme Linked Immunosorbent Assay

The enzyme linked immunosorbent assay, commonly known as ELISA, is a widely used analytical biochemistry technique used primarily to detect the presence of a substance in a liquid sample. Since its development in the 1970s, the ELISA technique has revolutionized biomedical research and diagnostics due to its high sensitivity and specificity.

What is ELISA?
ELISA is an antibody-based biochemical technique used to detect the presence of antigens or antibodies in a liquid sample using a colorimetric technique. The word ‘enzyme’ refers to the use of an enzyme conjugate as a marker to trace the antibody or antigen. ‘Linked’ implies the linking or attachment of the enzyme to the antibody or antigen. ‘Immunosorbent’ denotes that an immunological reaction, in the form of antigen-antibody binding takes place between immobilized capture antibodies on the solid support and the antigen or antibodies in the fluid phase. The addition of substrate to the enzyme conjugate results in a color change that can be easily detected. The intensity of the color developed is proportional to the quantity of antigen or antibody present in the original sample. This forms the basis of the ELISA technique.

Types of ELISA
There are four basic types of ELISA techniques:

1. Direct Enzyme Linked Immunosorbent Assay: Used for detection of antigens where antigen is directly coated onto the microwell plate and enzyme-conjugated primary antibody is used for detection.

2. Indirect ELISA: Used to detect antibodies where primary antibody is coated and antigen linked to enzyme-conjugated secondary antibody is used for detection.

3. Sandwich ELISA: Both capture and detection antibodies bind to different epitopes on the target antigen. Used to detect antigens directly from samples.

4. Competitive ELISA: Uses labeled antigen that competes with unlabeled antigen present in the sample for binding to capture antibodies. Used to quantify small molecules.

Applications of ELISA
Due to its high sensitivity and specificity, ELISA has found widespread applications in various fields like infectious disease diagnosis, food safety, environmental monitoring, endocrinology and cancer research. Some key applications include:

- Diagnosis of HIV, hepatitis B & C, STD infections like syphilis.
- Detection of hormones, cytokines and tumor markers.
- Screening of blood, plasma and serum donations for infectious agents.
- Detection of pesticide and antibiotic residues in food and water.
- Quantitative measurement of hormones, proteins, antibodies and other biomolecules.
- Detection of allergens in food and environmental samples.
- Detection of biomarkers for cancer diagnosis and prognosis.

Future Prospects
The ELISA technique is constantly being improved upon and new variations are being developed to address emerging analytical needs. Some promising future areas include:

- Multiplex/Array ELISA for simultaneous detection of multiple analytes in a single well or panel.

- Paper-based and 3D printed microfluidic ELISA devices for point-of-care diagnostics in resource limited settings.

- Lateral flow strip ELISA for simple visual detection of analytes without need for instrumentation.

- Digital/quantitative ELISA using novel optical or electrochemical detection schemes for better quantification.

- Single molecule ELISA for ultra-sensitive detection at sub-attomole levels.

- Protein microarray-based ELISA for high-throughput protein expression profiling and biomarker discovery.

 

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