View source for Immunodiffusion

Immunodiffusion reactions are diagnostic tests that use the diffusion of particles through a medium (such as agar) to measure:
*relative concentrations of antibodies/antigens
*relative purity of an antigen preparation

There are two types of immunodiffusion reaction, both being carried out on a semisolid medium:
*'''radial immunodiffusion''': also known as the Mancini method. The medium is prepared with a suitable dilution of antiserum and the antigen sample placed on top and allowed to diffuse. As diffusion takes place,  large insoluble complexes form creating a ring of precipitation (precipitin). By comparing the area of the ring with a standard curve, the concentration of the antigen sample can be determined. 
*'''double immunodiffusion''': also known as the Ouchterlony method. Antigen and antibody preparations are placed on the medium and both allowed to diffuse radially from the wells towards each other. This establishes a concentration gradient, forming an area of equivalence and line of precipitin.