Phage-borne peptidomimetics accelerate the development of polyclonal antibody-based heterologous immunoassays for the detection of pesticide metabolites

Competitive immunoassays for the detection of small analytes, such as pesticides and their metabolites, use haptens that compete with the target compounds for binding to the antibody. This competing hapten can be either the same as the immunizing hapten (homologous assay) or structurally modified mimics of the immunizing hapten (heterologous assay). Polyclonal antibody-based heterologous immunoassays have shown superior sensitivities to homologous ones, butthe synthesis of heterologous haptens may be time-consuming, requiring expertise in synthetic chemistry. In this work we demonstrate that phage display peptide libraries can be used as a source of phage-borne peptidomimetics to facilitate the development of sensitive heterologous assays. Different strategies for the isolation of these peptides were explored using two metabolites of pyrethroid insecticides. The sensitivities of the best competitive phage heterologous enzyme-linked immunosorbent assays were 13 fold and 100 fold better than the homologous assay, for the glycine conjugate of trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid and 3-phenoxybenzoic acid, respectively. The phage particles were highly versatile as tracer reagents, allowing the use of enzymatic, chemiluminescent, or immuno-polymerase chain reaction detection. The data presented here shows a new systematic procedure that enables the fast generation of several competing haptens for the rapid development of sensitive heterologous immunoassays.