Electrochemical immunosensors and monitoring environmental pollutants

A practical immunosensor for environmental monitoring should be specific, reversible, able to provide fast response time, and capable of direct detection of an immunoreaction, with minimal sequential addition of immunoreagents. Also, the sensor should be capable of continuous flow measurements and have capabilities to determine multiple analytes in complex samples, with no need for sample preparation steps. Finally, the immunosensor system should be able to process signals, and be suitable for integration into other devices that can excercise real-time feedback as required for pollution monitoring. Although a number of sensing methods for the measurement of pollutants have been reported, very few address these specific requirements. The combination of electrochemical immunosensors with flow injection analysis offers great advantages in the development of readily automated, high sample throughput, compact, and moderately inexpensive instrumentation that can satisfy (or are potentially able to satisfy) the above-mentioned criteria. The United States Environmental Protection Agency, Las Vegas, is carrying out research in the development of immunosensors to study the release of pollutants into the environment for human exposure studies. The system involves the use of an electrochemical transduction principle for measurements in liquids. The sensor consists of a portable, low-cost, electronic module which sends an electrical potential wave across a flowing sample, and a reference electrode that is sensitive to potential changes at the surface of an electronically responsive polymer membrane. Reversible analyte recognition is achieved by using antibody-protein molecules having specificity and affinity for the target analytes. The system can be used as an alarm station for early detection and full-time surveillance of pollution in groundwater, waste stream effluents, agricultural run-offs and for monitoring the effectiveness of remediation. The reversible control of the antibody-antigen interaction is particularly crucial to the development of a renewable sensor surface. First, a large number of important biological and environmental molecules can be detected in real time, as opposed to the use of a complex biochemical procedure. Secondly, there is no net degradation of the sample. As the assays are produced electrochemically, there is also a clear path to their implementation on interdigitated microelectrode arrays. This yields the advantages of improved sensitivity, multi-analyte sensing, and the possibility of integration into other devices for convenient signal processing. This paper described an overview of electroanalytical techniques employed for immunological detection, and discussed the development of an on-line immunosensing system using the detection and quantitation of polychlorinated biphenyls as a test case.