Homogeneous and Heterogeneous Enzyme Immunoassays Monitored with Carbon Dioxide Sensing Membrane Electrodes

Abstract

Immunochemical Potentiometric and amperometric electrodes are in the infant stages of development, yet the literature is already replete with diversified efforts to design increasingly sensitive and specific immunoelectrodes (Eggers et al., 1982; Guilbault, 1983; Boitieux et al., 1984; Keating and Rechnitz, 1984). The carbon dioxide gas-sensing probe, however, has played only a limited role in this research. Despite all the schemes designed for immunosensors, there is a conspicuous absence in the use of the carbon dioxide probe. Why this might be so is suggested by the constraints within which use of the carbon dioxide probe is practical as well as the limiting characteristics of the immunochemical reaction being studied. Additional restrictions result from the presence of the enzyme when developing an enzyme immunoassay [EIA]. Despite this, the enzyme is a favorite “transducer”, or label, which produces a signal related to the immunochemical reaction and can be recognized by the electrochemical detector. This integration of enzyme chemistry, immunochemistry and probe characteristics is a critical factor in determining, during method development, the feasibility of selecting a carbon dioxide probe as the analytical detector. These key ingredients will be discussed in this overview together with possibilities for the future of the carbon dioxide sensor in immunochemical applications. Improvements in the probe and broader applications will highlight this future.