Double-antibody separation method procedure

Heterogenous fluorescence immunoassays can be carried out with the aid of the same separation procedures used in radioimmunoassay. The more expedient homogenous fluorescence immunoassays require quenching, enhancement, polarization, or shifting of the fluorescence of the label upon binding of the labeled analyte to its antibody. Occasionally, a second antibody, directed at the anti analyte antibody, will be used in a double-antibody method to precipitate the bound labeled and unlabeled analyte or to alter the optical properties of the label in such a way as to make the analysis more sensitive. 

Solid-phase procedures are also applied for separation of free antigen (or free antibody). It is also possible to precipitate antibodies by double immunoprecipitation technique in the presence of an excess of anti-IgG. However, this method is not fully reliable since a dissolution of the complex can take place in the presence of an excess of antibodies. 

---