Abstract
An enzyme-linked immunosorbent assay (ELISA) was developed for the neonicotinoid insecticide imidacloprid, 1-[(6-chloro-3-pyridinyl)methyl]- N-nitro-2-imidazolidinimine using monoclonal antibodies (MAb). Three MAbs, designated as E6A6, E6F3 and H7F7, were raised from mice immunized with an imidacloprid hapten–ovalbumin conjugate. These MAbs performed similarly in indirect competition ELISA (icELISA), so one, E6F3, was selected for detailed study. The equilibrium constants ( K d) and association and dissociation rate constants ( k on, k off) for five neonicotinoids and one imidacloprid metabolite to E6F3 were determined by kinetic exclusion fluoroimmunoassay (KinExA). Affinities (1/ K d) of E6F3 for acetamiprid and clothianidin were similar, but 50-fold weaker than that of imidacloprid. MAb E6F3 had no measurable affinity for the other neonicotinoids. The icELISA can tolerate up to 15% (v/v) acetone or 20% (v/v) methanol. Assay sensitivity was similar at pH 4–9, 1–10-fold concentration of PBS with or without 0.05% Tween 20, and incubation times of 30–180 min. The half-maximal inhibition and the limit of detection were approximately 0.8 and 0.1 μg/l of imidacloprid in icELISA, and 0.3 and 0.03 μg/l in direct competition ELISA (dcELISA), respectively. Analysis of imidacloprid-fortified water and cucumber samples by the icELISA showed average recoveries from 70 to 120%.
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