Immobilized Biomolecules for Detection of Environmental Pollutants

Abstract

Biosensors which incorporate immobilized enzymes, receptors, antibodies or microbes have been used to measure compounds of environmental significance as diverse as phenolics, ammonia, formaldehyde, benzo(a)pyrene, PCBs, and pesticides. Although a variety of biosensor assay formats have been reported, there are two basic mechanisms for operation: detection of a substrate or product of biocatalysis, and detection of a stoichiometric binding event. Most reported biosensors use one or the other of these mechanisms. Herein reported, however, are two unique biosensors which use both mechanisms to detect organophosphate (OP) and carbamate pesticides. Most OP and some carbamate pesticides bind stoichiometrically to, and inhibit acetylcholinesterase (AChE) activity. Consequently, biosensors using this enzyme are able to catalytically amplify the binding event. Two AChE-based biosensors were developed using different enzyme immobilization and signal transduction schemes. The fiber-optic biosensor uses a fluorescein isothiocyanate (FITC) label to report AChE activity. Signal transduction was accomplished by catalysis-induced pH changes in the local environment of the enzyme which changed the optical properties of the FITC probe. The AChE-based light addressable Potentiometrie (LAP) biosensor measures AChE immobilized to a nitrocellulose membrane. Signal transduction in this case was accomplished using the LAP transducer which is sensitive to small changes in surface potential resulting from AChE-induced pH changes in solution. Both of these biosensors responded similarly to various OP and carbamate pesticides despite the use of dramatically different enzyme immobilization and signal transduction schemes.