ELISA for semicarbazide and its application for screening in food contamination

The development of a direct competitive enzyme-linked immunosorbent assay (ELISA) based on polyclonal antibodies specific for semicarbazide (SEM) is described. Molecular modelling of the hapten mimics and other key components of the assay system was conducted to explain antibody properties in relation to hapten design. The small aliphatic molecule SEM was coupled to 3-carboxybenzaldehyde to produce carboxyphenyl-SEM (CPSEM), for the generation of specific antibodies. Five rabbits produced antibodies against NPSEM (used in direct and indirect ELISA formats) exhibiting a 50% binding inhibition level (IC₅₀ values) of 0.06-2.28 μg L⁻¹ in assay buffer for SEM. The most sensitive indirect assay based on the antibody MVK39 showed a high dynamic range providing a linear readout in the range of 0.01-0.2 μg L⁻¹. Antibody MVK31 (IgG) allowed specific SEM detection at an IC₅₀ = 0.14 μg L⁻¹ in direct ELISA and was evaluated using solvent extracted SEM-spiked porcine and baby food samples. Recovery levels determined from fortified samples (0.5, 1.0, 1.5, 5, 10 and 20 μg kg⁻¹) of porcine and baby food ranged from 82.9 to 105.3%, respectively, with a coefficient of variation less than 15.5%. Respective detection capability and threshold of the assay for porcine muscle, set on the basis of acceptance of no false negative results, was 0.3 and 0.11 μg kg⁻¹.