[1] This assay makes use of two component fragments of an enzyme which are each individually inactive.

Under the right conditions in solution these fragments can spontaneously reassemble to form the active enzyme.

For use in biochemical assays, one of the enzyme fragments is attached to an analyte of interest.

To determine the quantity of analyte in a sample, an aliquot of sample must be added to a solution containing enzyme-fragment-analyte-conjugate, the other enzyme fragment, antibody directed against the analyte and substrate for the enzyme reaction.

Conversely, low concentrations of analyte in the sample lead to a relatively large amount of the enzyme-fragment-analyte-conjugate being prevented from forming active enzymes and therefore low enzyme activity.