Affinity patterns of enzyme tracers for triazine immunoassays

Cross-reactivities are one of the most important characteristics of immunoassays. Nevertheless most cross- reactivity studies are only performed with small molecules, which are similar to the target analyte. The complex mechanism of the binding event of an antibody makes it likely that the orientation of the hapten plays a critical role. Therefore cross-reactivities of hapten-derivatives with spacers may be quite different compared to the simple compound, especially when the spacer has been coupled to a large molecule, like a marker enzyme (e.g. peroxidase). We examined the relative affinity patterns of 17 enzyme tracers to 16 monoclonal and polyclonal antibodies for the analysis of triazine herbicides (atrazine, terbuthylazine, etc.). This allows interesting discussions about the structure of the antibody binding site and the comparison of antibodies generated with different immunogens. In addition, some general rules for the selection of immunogen structures could be derived from the data. The figures shown in this paper facilitate to find suitable tracer haptens for one of the tested antibodies and support for instance the optimization of immunosensor regeneration, as tracer affinity is closely correlated to the dissociation rate constant of an antibody-tracer complex.