ELISA, which stands for Enzyme-Linked Immunosorbent Assay, is a foundational technique in biomedical research and diagnostics. Its core principle leverages the highly specific binding reaction between an antigen and its antibody, amplifying and visualizing this interaction through an enzymatic colorimetric reaction. This allows for the qualitative or quantitative detection of extremely trace amounts of a target substance (antigen or antibody).
Enzyme-labeled antibody technology is a labeling technique that involves covalently conjugating enzyme molecules to specific antibodies. Its core principle is: utilizing the antibody's high specificity for antigen recognition as a "targeting system" to precisely locate the target molecule; then, leveraging the enzyme's highly efficient catalytic "amplification effect" on its substrate to convert an invisible immune reaction into a visible or instrument-detectable signal (such as a color change, luminescence, etc.). This enables the qualitative, locational, or quantitative analysis of the target antigen or antibody.
ELISA is one of the fundamental experiments in immunology, and most researchers in the life sciences field are familiar with it. Owing to its characteristics of strong specificity, high sensitivity, and accurate quantitation, ELISA technology is widely applied in both basic scientific research and clinical diagnosis. It is believed that many of our followers who pay attention to us have also performed ELISA experiments. We have compiled a list of common issues that may arise during ELISA experiments for your reference.
The most commonly used solid-phase carrier in ELISA is the microplate made of polystyrene. Its adsorption of proteins forms the basis of the entire detection system, and the core principle behind this lies in the non-covalent interactions between the surface of the solid-phase material and protein molecules.
Coating is the process of immobilizing specific antibodies or antigens on the surface of a solid-phase carrier. Its quality directly affects the sensitivity, specificity, and reproducibility of the experiment. It is equivalent to building an "exclusive reaction platform" for subsequent antigen-antibody reactions.
These three techniques(RIA,ELISA,Westernblot) are fundamental immunoassay techniques in biomedicine, used to detect specific biomolecules (such as proteins, hormones, antibodies). Their core differences lie in their detection principle, target molecule, sensitivity, specificity, throughput, and application.
There are different opinions on the detection and classification of ELISA, and different literatures have different classification opinions in terms of principle or operation. Here we divide ELISA into the following four categories, and then explain each category in detail: (1) direct ELISA; (2) indirect ELISA; (3) Sandwich ELISA; (4) Competition inhibits ELISA. Other ELISA are affiliated with, or derived from, a combination of these four types of ELISA.
Depending on the detection purpose, common types of ELISA include the indirect method (for measuring antibodies), the double antibody sandwich method (for measuring antigens), and competitive methods. Among these, the double antibody sandwich method and the indirect method are the most widely used. The following example will detail the standard operating procedures and key considerations for the double antibody sandwich method.
High background No signal Too much signal - whole plate turned uniformly blue Standard curve achieved but poor discrimination between points Poor duplicates Poor assay to assay reproducibility No signal when a signal is expected, but standard curve looks fine Samples are reading too high, but standard curve looks fine Very Low Readings Across the Plate Green color develops upon addition of stop solution when using streptavidin-HRP Edge Effects
