Many immunoassays make use of enzymes as labels. Following antibody binding of target a suitable substrate is added to the reaction vessel. The signal arising from enzyme activity on this substrate can then be recorded. To stop enzyme activity a volume of stop solutiong specific for the enzyme/substrate pair is added to the reaction vessel. This will stop the reaction by altering the conditions within the vessel away from the optimal conditions of enzyme activity. Synonyms: Stop Solution, Elution Reagent.