An analytical device for on-sight immunoassay: demonstration of its applicability in detection of DDT in food samples.

A simple analytical device was developed for performing non-instrumental
immunoassay. The device consists of membrane with antibody-coated zones
and filter pad acting as an absorbent body. Very low concentrations of DDT in
food samples were estimated by using an improved catalysed reporter deposition
I-CARD method. The signal amplification involved biotinylated tyramine and
avidin�alkaline phosphatase (ALP) conjugate. 5-Bromo-4-chloro-3-indolylphosphate
in conjunction with nitro blue tetrazolium was used for colour
visualisation. Semi-quantitative results were obtained by visual comparison of the
colour intensity of the sample spot with those of reference standards. Quantitative
estimation is possible by densitometry using CCD camera. A batch of five
extracted samples could be analysed in a single kit within 30 minutes. Spiked
samples were analysed without sample cleanup. The possible matrix interference
was analysed. The results were comparable with gas chromatography and CCD
analyses. The method is well suited for visual screening of food samples for DDT
under field conditions.