Molecular aspects of design of immunoassays for drugs

An understanding of the molecular structure of the antibody binding site, the epitope complementary to the antibody, and the intermolecular forces that determine the affinity and specificity of the interaction of antibody and epitope is fundamental to the design of immunoassays. This is particularly important for haptens because their small size results in small changes in substituent functional groups, e.g., optical rotation and carboxyl substitution for amide resulting in large changes in binding affinity. It should be possible to predict the effect of haptenic structure on binding affinity by considering the resulting changes in balance between the different intermolecular forces. This information can be used in designing immunogens and modifying the reaction conditions used during assay optimization, such as pH or ionic strength, that enhance the predominant intermolecular forces to increase the binding affinity but leave minimal matrix effects. Improved understanding of the molecular aspects of the immunological interaction can facilitate more rapid and economic immunoassay development.