Introduction aux Tests ELISA

Introduction to ELISA Tests

• ELISA (Enzyme-Linked Immunosorbent Assay) are widely used lab techniques to detect and quantify various substances like proteins, peptides, antibodies, and hormones.
• The technique utilizes antibodies and enzymes to produce a measurable signal, typically a color change.

ELISA Direct

• Principle: The antigen is directly attached to the plate, and an enzyme-linked antibody binds to it.
• Advantages: Faster procedure with less risk of cross-contamination.
• Disadvantages: Lower sensitivity, suitable only for high antigen levels.

ELISA Indirect

• Principle: Antigen is attached to the plate, a primary antibody binds to the antigen, followed by an enzyme-linked secondary antibody.
• Advantages: Higher sensitivity due to signal amplification; multiple secondary antibodies can bind to a single primary antibody.
• Disadvantages: Risk of cross-reactions with the secondary antibody and a longer procedure.

ELISA Sandwich

• Principle: Two capture antibodies are attached to the plate, targeting different epitopes on the same antigen. A third detection antibody with an enzyme binds to the captured antigen.
• Advantages: Enhanced sensitivity and specificity, useful for complex proteins with multiple binding sites.
• Disadvantages: More complex procedure, requiring well-characterized and compatible antibodies.

ELISA Competitive

• Principle: The sample antigen competes with a labeled antigen for binding to an antibody on the plate.
• Advantages: Suitable for low antigen concentrations.
• Disadvantages: More complex analysis, as the sensitivity depends on the competition between antigens.

General ELISA Steps

• Immobilization: Binding antigen or antibody to a microtitration plate.
• Blocking: Preventing non-specific binding with a blocking solution.
• Binding: Introduction of the sample containing the analyte.
• Detection: Adding an antibody or an enzyme-labeled antigen.
• Washing: Removal of unbound components.
• Substrate: Addition of an enzymatic substrate to produce a signal (usually colorimetric).
• Reading: Measurement of the signal using a plate reader.

Applications of ELISA

• Medical diagnosis (e.g., HIV, COVID-19, autoimmune diseases).
• Biological and immunological research
• Quality control in food and pharmaceutical industries.
• Environmental monitoring (contaminant detection).