Precipitation test in gel

Precipitation test in gel

The gel phase precipitation test (gelphaseprecipitation) is to use soluble antigen and the corresponding antibody to diffuse in the gel to form a concentration gradient, where the antigen and antibody meet and the concentration ratio is appropriate to form a visible precipitation line or precipitation ring. Commonly used gels include agar, agarose, dextran, or polyacrylamide gels, which are prepared with physiological saline or buffer according to the test requirements. A gel with a suitable concentration is actually a solid phase buffer, with water accounting for more than 98%. The gel forms a network structure, which solidifies the water, and antigens and antibody proteins diffuse in the gel as if in a liquid Free movement. Macromolecules (with a molecular weight of more than 200,000) diffuse slowly in the gel. This feature can be used to identify differences in molecular weight. In addition, due to the limited size of the gel mesh, the molecular weight of the complex should be at least one million or more after the antigen and antibody are bound. This super-large molecule is trapped in the gel by the network, and only free antigen can be removed by immersion in saline. Or antibodies, which brings great convenience to the subsequent analysis.

According to the way and characteristics of the reaction between antigen and antibody, the precipitation test in the gel can be divided into one-way diffusion test and two-way diffusion test.

The single-diffusion test (singlediffusion test) is to mix a certain amount of antibody in the agar gel to allow the antigen solution to be tested to diffuse freely from the local area into the agar, forming a visible precipitation ring in a certain area. According to the test form, it can be divided into test tube method and flat plate method.

The double diffusion test (doublediffusion test) is to allow both antigens and antibodies to diffuse to each other in agar, forming an antigen-antibody precipitation line at an appropriate ratio. Observe the position, shape and contrast relationship of this precipitation line. Perform qualitative analysis. According to the test form, it can also be divided into test tube method and flat plate method.