Investigation of the effect of hapten heterology on immunoassay sensitivity and development of an enzyme-linked immunosorbent assay for the organophosphorus insecticide fenthion

Abstract

In a previous study of ours, a new synthetic method for haptens of organophosphorus (OP) pesticides, with a spacer arm (aminocarboxylic acid) attached at the thiophosphate group, was developed and applied to the synthesis of haptens for the OP insecticide fenthion. Polyclonal antibodies were obtained from the haptens that were conjugated to carrier proteins. In this study, the effect of hapten heterology on immunoassay sensitivity was investigated using the antibodies and several plate-coating haptens with different types of heterology. The findings were that the degree of hapten heterology parallels the degree of sensitivity. Using the most suitable plate-coating antigen, an indirect enzyme-linked immunosorbent assay (ELISA) for fenthion was developed. The IC 50 value of fenthion, under optimum conditions, was estimated to be 16 ng/ml with a detection limit of 1 ng/ml. The antibodies showed negligible cross-reactivity with other OP pesticides except with the insecticide fenitrothion. Recoveries of fenthion from fortified rice and vegetable samples ranged between 85 and 113%.