A direct optical immunosensor for atrazine detection

Abstract

Immunoanalytical techniques represent one of the most important applications of biomolecules in analytical procedures. Direct monitoring of immunoreactions by an analytical device is a particularly attractive approach to environmental sensing as it offers speed, a simple test scheme and does not require labelled compounds. Target limits of detection for pesticides are imposed by the EU drinking water act (0.1 μg/l for a single pesticide). A competitive test format with surface immobilised antigen is common for pesticide detection with direct immunosensors. Free pesticide binds to antibody in solution decreasing the amount of antibody binding to the transducer. As the concentration of antibody in a competitive test must be comparable to the concentration of the analyte (0.1 ppb atrazine ≈ 0.5 nM), the transducer must be able to resolve changes in antibody concentration below 1 nM. A prototype atrazine sensor based on reflectometric interference spectroscopy (RIFS) was investigated. The slope of the binding curve was used as a measure for antibody concentration. Binding curves of monoclonal anti-atrazine to an atrazine-modified surface were recorded at different concentrations. A reproducibility of 10% was found for the determination of antibody concentrations (100 to 1000 ng/ml). In competitive binding experiments with free atrazine inhibition of 50% was observed at 0.5 ppb atrazine (500 ng/ml antibody) and at 1 ppb (1 μg/ml antibody). The results are discussed with respect to the theoretical performance of the device and practical requirements. A comparison to other optical transducers and a critical discussion about the feasibility of direct optical immunosensors in pesticide detection is given.