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) detec tion was developed. The assay was based on the competitive reaction of 2,4- D and enzyme tracer with monoclonal antibodies immobilised on an Ultrabind( R) membrane. The binding of enzyme tracer on the test strip was determined by a simple, portable reflectometer as remission at 657 nm. Using this tech nique, 2,4-D could be detected in a concentration range of 0.5 mu g/L to 10 0 mu g/L. The center point of the 2,4-D test was found at a concentration o f 6 mu g/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 t echnique using microtiter plates. The assay was applied in the detection of 2,4-D in real water samples, and sensitivity was comparable to spiked wate r samples. If combined with an effective extraction procedure that results in recovery rates of 90%, the dipstick assay can be used to monitor human e xposure to 2,4-D from contamination in water, from oranges and in testing u rine samples.