A Membrane-Based ELISA Assay for the Herbicide Isoproturon in Soil Samples

Abstract

A membrane based enzyme linked immunosorbent assay (MELISA) for the detection of a common herbicide, isoproturon is described. A heterogeneous competitive ELISA was the format chosen for isoproturon detection. An immunoassay system with a horseradish peroxidase (HRP) labeled polyclonal antibody preparation was developed and characterized before suitable sensitivity and selectivity for isoproturon were attained. After development as a microtiter plate immunoassay, the system was transferred to an affinity membrane sorbent based ELISA where the isoproturon/ovalbumin conjugate was immobilized on commercial membranes. Different porosities and immobilization conditions were utilized to optimize the MELISA, including sensitivity, selectivity, and stability studies. This enabled detection of isoproturon in the range 0.5 ng ml⁻¹–20 µg ml⁻¹, with an LLD90 of 0.5 ng ml⁻¹. The use of acetonitrile extracts from soil samples was found to not overly impair the performance of the MELISA. Good correlation between ELISA and HPLC was obtained for extracts from spiked soil samples.

Keywords:

• Herbicides
• Immunoassay
• Isoproturon
• Soil analysis

Acknowledgments

The authors would like to express their gratitude to Dr Ramadan Abuknesha (Kings College London, UK) for providing the antibodies and the late Prof. Allen Walker (HRI, Wellesbourne, UK) for the soil samples, also the BBSRC (UK) for financial support through a BBSRC-Case studentship scheme.