Affinity
Definition
The binding strength of a single antigen-binding site for one epitope, expressed as the equilibrium dissociation constant (Kd). A lower Kd indicates tighter binding. High-affinity antibodies are preferred in forensic immunoassays because they maintain binding at low antigen concentrations.
- Measured by
- Equilibrium dissociation constant Kd
- Relationship
- Lower Kd means tighter binding
- Scope
- Single binding site to single epitope
- Forensic preference
- High-affinity antibodies for immunoassays
Common questions
Why do forensic immunoassays specifically need high-affinity antibodies?+
Forensic samples such as bloodstains or trace residues often contain very little antigen, and a high-affinity antibody stays bound and detectable at those low concentrations where a weaker antibody would dissociate and give a false negative.
How does affinity differ from avidity, a related term?+
Affinity describes the strength of one binding site to one epitope, while avidity describes the combined strength of an antibody's multiple binding sites acting together, which can be much higher than any single site's affinity alone.
Related terms
- Complementarity-Determining Regions (CDRs)
- Six hypervariable loops, three in the heavy-chain variable domain and three in the light-chain variable domain, that together form the antigen-binding site....
- 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...
- Fab Fragment
- The antigen-binding fragment of an antibody, consisting of one complete light chain paired with the variable and first constant domain of a...
- Fc Region
- The crystallisable fragment of an antibody, formed by the paired constant domains of the two heavy chains. The Fc region mediates effector...
- Monoclonal Antibody (mAb)
- An antibody produced by a single hybridoma clone, so that every molecule in the preparation is identical, targets the same epitope, and...