Sandwichimmunoassays

Sandwich immunoassays are a type of immunoassay used to detect and quantify the presence of a specific antigen. This assay utilizes two antibodies that bind to different epitopes of the target antigen. The assay is typically performed in a solid phase, such as a microplate well or a membrane strip. In the most common format, the first antibody, often referred to as the capture antibody, is immobilized onto the solid phase. The sample containing the antigen is then added to the well. If the antigen is present, it will bind to the capture antibody. Following a washing step to remove unbound substances, a second antibody, known as the detection antibody, is added. This detection antibody is conjugated to a detectable label, such as an enzyme, fluorescent molecule, or radioactive isotope. The detection antibody binds to a different epitope on the captured antigen, forming a "sandwich" complex of capture antibody, antigen, and detection antibody. After another washing step, the signal generated by the label on the detection antibody is measured. The intensity of this signal is proportional to the amount of antigen present in the sample. Variations of the sandwich immunoassay include direct sandwich, indirect sandwich, and capture sandwich formats, differing in how the antibodies are labeled and detected. Sandwich immunoassays are widely used in clinical diagnostics, research, and food safety testing due to their high sensitivity and specificity.