Enzyme Conjugate
Definition
An antibody (or antigen) chemically linked to a reporter enzyme, most commonly horseradish peroxidase (HRP) or alkaline phosphatase (AP). The enzyme catalyses a colour-generating reaction in the detection step, linking the immunological binding event to a measurable optical signal.
- Common enzymes
- Horseradish peroxidase (HRP), alkaline phosphatase (AP)
- Function
- Links antibody binding to a measurable colour signal
- Attached to
- An antibody or antigen
Common questions
Why is an enzyme rather than a direct label used to detect the binding event?+
The enzyme amplifies the signal by continuously converting many substrate molecules into coloured product for as long as the reaction runs, producing a stronger and more measurable readout than a single fixed label attached to each binding event.
Does the choice between HRP and AP conjugates affect assay sensitivity?+
Yes. The two enzymes use different substrates and kinetics, and a laboratory selects one over the other based on the required sensitivity, substrate stability, and any interference expected from the sample matrix.
Related terms
- Competitive ELISA
- An ELISA format in which sample antigen competes with a fixed quantity of labelled antigen for a limited number of antibody binding...
- Cross-Reactivity
- The capacity of an antibody raised against one analyte to bind structurally related compounds. In RIA, cross-reactivity is the main driver of...
- Sandwich ELISA
- An ELISA format in which a capture antibody immobilised on the plate binds one epitope of the target antigen, and a separate...
- Solid Phase
- The inert surface to which an antigen or antibody is adsorbed at the start of an ELISA. Usually the well walls of...
- Substrate
- The compound converted by the reporter enzyme into a coloured product. For HRP, 3,3',5,5'-tetramethylbenzidine (TMB) is the standard substrate, producing a blue...