Chemiluminescent immunoassay: Application of a portable scanning luminometer for the determination of 2,4‐dichlorophenoxyacetic acid in microtiter and membrane strip format

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Abstract
A sensitive competitive immunoassay with chemiluminescent detection for the determination of 2,4‐dichlorophenoxyacetic acid (2,4‐D) was carried out in a microtiter and membrane strip format. The application of a portable scanning luminometer for the detection of light emission in polystyrene strips and from the surface of a porous membrane resulted in an increase in the sensitivity of the assay and a wider detection range when compared to conventional colorimetric detection. With the assay in microtiter strip format, 2,4‐D can be determined within the range 0.005–1 μg l‐1 with an IC50 at 0.04 p.g l‐1. Different immobilization techniques involving adsorption and covalent immobilization on different kinds of modified nylon were examined to optimize the attachment of specific antibodies to the surface of porous membranes. Photoimmobilization on positively charged nylon modified with p‐azidobenzoic acid was found to result in higher sensitivity. The application of a membrane strip format allows the quick quantitative detection of 2,4‐D at concentrations above 0.02 μg l‐1. Both tests in microtiter and membrane strip formats can be performed under field conditions for the screening of water samples.