Development of a dipstick immunoassay for quantitative determination of 2,4-dichlorophenoxyacetic acid in water, fruit and urine samples

A sensitive dipstick assay for 2,4-dichlorophenoxyacetic acid (2,4-D) detection was developed. The assay was based on the competitive reaction of 2,4-D and enzyme tracer with monoclonal antibodies immobilised on an Ultrabind^? membrane. The binding of enzyme tracer on the test strip was determined by a simple, portable reflectometer as remission at 657 nm. Using this technique, 2,4-D could be detected in a concentration range of 0.5 μg/L to 100 μg/L. The center point of the 2,4-D test was found at a concentration of 6 μg/L. Cross-reactivity with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) as determined by this dipstick assay was 2.5% and 3% by standard ELISA technique using microtiter plates. The assay was applied in the detection of 2,4-D in real water samples, and sensitivity was comparable to spiked water samples. If combined with an effective extraction procedure that results in recovery rates of 90%, the dipstick assay can be used to monitor human exposure to 2,4-D from contamination in water, from oranges and in testing urine samples. Received: 2 September 1998 / Revised: 29 January 1999 / Accepted: 31 January 1999