A "sandwich" one of these utilizes a separate mounted (*) antibody to perform specific capture, in contrast to the indirect version where the sample of interest is fixed to the surface by adsorption.  
Newer variations of it include a reverse technique and a variant based on competitive binding.  A "sandwich" one of these utilizes a separate mounted (*) antibody to perform specific capture, in contrast to the indirect version where the sample of interest is fixed to the surface by adsorption.  Detection is usually carried out through the action of an enzyme such as alkaline phosphatase or horseradish peroxidase on a chromogenic or fluorogenic substrate.  Having largely supplanted methods requiring autoradiographic detection, for 10 points, this is what biochemical technique that determines the concentration of an antigen based on its binding to antibodies?
Newer variations of it include a reverse technique and a variant based on competitive binding.  
{ELISA} or {Enzyme-Linked Immunosorbent Assay} or {EIA }or {Enzyme Immunoassay} (4) [AU]