What is Enzyme-Linked ImmunoSorbent Assay (ELISA)?

Enzyme-Linked ImmunoSorbent Assay, or ELISA, is an immunoenzymatic technique that emerged following the development of immunofluorescence and radioimmunoassay technologies. Since its inception in the early 1970s, ELISA has experienced rapid growth.

ELISA is a rapid detection technique established on the basis of the specific binding reaction between antigens and antibodies. It ingeniously combines the high efficiency of enzyme-catalyzed reactions with the exceptional specificity of immune responses. This method allows for the determination of various trace organic compounds with precision.

Brief Insights into Antigens and Antibodies

Antigens are substances capable of eliciting a specific immune response within an organism. Upon entering the body, antigens can trigger cellular immunity and antibody production. The reactivity of antigens is contingent upon antigenic determinants or epitopes. A single antigen molecule may possess various determinant clusters, contributing to its diverse interactions within the immune system.

Schematic diagram of antigen-antibody binding reaction

Antibodies refer to immunoglobulins capable of specific binding to antigens.

The relationship between antigens and antibodies is analogous to that of a specific key and lock—each pair corresponds uniquely. Only when the correct key, the antigen, is found can it unlock the corresponding lock—the antibody.

02 Principle of enzyme-linked immunosorbent assay

indirect method

  1. Facilitate the binding of antigens or antibodies to the surface of a solid-phase carrier while maintaining their activity.
  2. Link antibodies or antigens with an enzyme to form enzyme-labeled antibodies or antigens.
  3. During the assay, allow the test antibodies (or antigens) and enzyme-labeled antigens (or antibodies) to react with the antigen (or antibody) on the surface of the solid-phase carrier in different steps.
  4. Employ washing methods to remove unbound enzyme-labeled antigens (or antibodies), with the final amount of enzyme bound to the solid-phase carrier being directly proportional to the quantity of the substance being tested in the sample.
  5. After adding the substrate for the enzyme reaction, the substrate is catalyzed by the enzyme to produce a colored product.
  6. The amount of the product is directly related to the quantity of the substance being tested in the sample, and qualitative or quantitative analysis can be conducted based on the intensity of the color reaction.

Classification of Enzyme-Linked ImmunoSorbent Assay (ELISA)

Indirect ELISA:
Coat known antigens onto a solid-phase carrier, and use enzyme-labeled secondary antibodies to detect unknown antibodies in the test liquid.

Schematic diagram of enzyme-linked immunosorbent assay (indirect method)

● Sandwich ELISA:

Coat known antibodies onto a solid-phase carrier, use enzyme-labeled primary antibodies, and detect soluble antigens in the test liquid.

Schematic Diagram of the Sandwich ELISA Process

Competitive ELISA:

Coat known antibodies or antigens onto a solid-phase carrier, use enzyme-labeled antigens or antibodies, and detect soluble antigens or antibodies in the test liquid.

Enzyme-Linked ImmunoSorbent Assay (Inhibitory Determination Method) Schematic

04 Advantages of Enzyme-Linked ImmunoSorbent Assay (ELISA)

  1. Fast Detection:
    • Can be prepared as dedicated test kits, allowing simultaneous testing of multiple samples and significantly reducing detection time.
  2. Strong Specificity:
    • Relies on the specific binding of antigens and antibodies, exhibiting a high level of selectivity.
  3. High Sensitivity:
    • Accuracy of results and sensitivity align with instrument analysis methods.
  4. Simple Operation:
    • No need for large equipment; test kits can be directly processed without secondary handling.
  5. Ease of Promotion:
    • Low technical requirements for personnel, facilitating easy technology dissemination.

05 Applications of Enzyme-Linked ImmunoSorbent Assay (ELISA)

Due to its characteristics of speed, convenience, and high sensitivity, ELISA is suitable for on-site testing. Its application scope continues to expand and is widely used in food and medical testing. In food testing, it is mainly employed for detecting pesticide residues in plant-based foods, veterinary drug residues in animal-based foods, mycotoxins, foodborne microorganisms, special proteins, heavy metals, and more.

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