Piezoelectric immunosensors for polychlorinated biphenyls operating in aqueous and organic phases

Abstract

The piezoelectric quartz crystal operating in the active mode was used as a transducer for construction of immunosensors for determination polychlorinated biphenyls (PCB). An apparatus for flow-through measurements with piezosensors in pure organic phase was constructed. The anti-PCB polyclonal antibody was immobilized in an oriented way via protein A on a smooth gold surface. The antibody high cross-reactivity for 2,4,4′-trichlorobiphenyl, 4,4′-dichlorobiphenyl and 3,3′,4,4′-tetrachlorbiphenyl allowed for a specific determination of these congeners in samples. PCBs were determined either directly or using competition with a tracer, synthesized from polystyrene particles by covalent attachment of 4,4′-dichlorobiphenyl (DCB). The direct piezoelectric immunosensor operated in phosphate buffer with 5% dimethylsulphoxide. It was possible to detect coplanar PCBs in the range 1–50 ppm. A higher detection limit is compensated here by the low cost and short time of analysis, below 20 min. The same immunorecognition layer can be used repeatedly. Furthermore, kinetic analysis based on a non-linear fitting of the recorded binding transients allowed for a detailed characterization of immunoaffinity interactions. For the more sensitive competitive assay, experiments were carried out directly in pure organic solvents. The most hydrophobic solvent, toluene, was selected due to the highest signal responses. The immunoreaction proceeded also quite well in the presence of dichloromethane and chloroform. However, rather low responses were obtained with acetonitrile and dimethylsulphoxide. The optimized method allowed us to detect PCBs in the range from 6 ppb to 1 ppm within 30 min using raw toluene extracts of soil samples without any purification or pre-concentration steps.