Investigation of highly sensitive piezoelectric immunosensors for 2,4-dichlorophenoxyacetic acid

The improved highly sensitive piezoelectric immunosensor has been developed and evaluated using a model interaction of antibody with the model hapten- herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). For immobilization of 2,4 -D, the self-assembled layers of cystamine, 4-aminothiophenol or 3,3'-dithi o-bis(propionic acid N-hydroxysuccinimide ester) were formed on smooth and rough crystals coated with gold or silver electrodes. The immunochemical in teractions performed well in all cases, the aminothiophenol on gold was cho sen as the optimum with regard to regeneration of immunosensing surfaces. T he kinetics of interaction of surface-bound 2,4-D with free antibody provid ed significantly higher kinetic parameters (kinetic association rate consta nt) when using optically smooth crystals compared to common rough crystal. Therefore. the smooth crystal should be preferred for future kinetic studie s. The competitive assay of the herbicide 2,4-D achieved a limit of detecti on of 10 ng/l using the monoclonal anti-2,4-D antibody F6C10. Finally, a di rect assay format has been evaluated using a thicker layer of glutaraldehyd e-crosslinked antibody on the sensing surface. The direct binding of a smal l herbicide molecule was follon ed in real time. The detected concentration of 2,4-D (5 mug/l) was low enough for future direct monitoring of this her bicide in water. (C) 2001 Elsevier Science B.V. All rights reserved.