Antibodies the keys to immunochemical measurements

Simply put, antigens are minute substances that evoke an immune response and are generally classihed as immunogens, tolerogens and allergens, each of which stimulates antibody production. While antigens are usually proteins or polysaccharides, they can be any type of molecule, including haptens (small molecules) covalently bound to carrier proteins (which facilitate transport in blood and into tissues or cells). 

Antibodies have three major properties, which provide the basis and characteristics of immunoassays  

From this equation, a given concentration of antigen ([Ag]) interacts with a given concentration of antibody ([Ah]) to form an antigen-antibody complex ([Ag-Ab]). This is a dynamic reaction which can occur in both directions, where is the so-called association rate constant working in opposition to K, which is the so-called dissociation rate constant. 

There are several key types of antibody-antigen reaction that are important to understand, which are as follows  

Liquid-phase and solid-phase reactions Antibody or antigen reactions can occur where both components are in the same liquid phase (in solution), or one component is in the solid phase and the other is in the liquid phase (solid-liquid interface). The former liquid phase assays were the first type used but have since largely been superseded by various forms of solid-phase immunoassay. Solid-phase assays 

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