Optical immunoprobe development for multiresidue monitoring in water

Aquifers used for drinking water production require regular monitoring for organic pollutants. Pollutant levels and pollutant patterns may change rapidly especially in surface water. Monitoring systems capable of unattended and automated operation are desirable e.g. at pumping sites. In this paper we report on a study of the application of immunoanalytical techniques for flexible and automated multiresidue testing. A solid phase fluorescence immunoassay with immobilised analyte derivate and free. fluorescence labelled antibody is used. Two optical transducers were tested: A simple 'slab'-waveguide made of sheet glass and an integrated optical (IO) waveguide. Bulk fluorophore excitation was used to estimate the performance of each transducer. Both transducers allow an antibody surface coverage of less than 1 parts per thousand of a monolayer of protein to be detected. The direct and covalent immobilisation of analyte derivates at the transducer surface for a binding inhibition assay approach is compared to a competitive assay with immobilisation of analyte derivates via an auxiliary antibody conjugate. The use of this auxiliary system allows the testing of different analytes at the same transducer surface. Atrazine was selected as a model analyte for the first trials. The ELISA type assay gives a test midpoint at 2.2 mu g/l and an estimated limit of detection of 0.3 mu g/l. The fluoroimmunoprobe with a binding inhibition assay has a test midpoint for atrazine at about 6 mu g/l. In the competitive assay with an auxiliary antibody conjugate signal levels were reduced by a factor of two and competition of free atrazine was poor. Titration with free analyte derivate (atrazine caproic acid) confirmed that this may be optimised by changing the competing derivate. (C) 1998 Elsevier Science B.V.