Selective Electrodes and Biosensors

Role of Polymeric Materials in the Fabrication of Ion-Selective Electrodes and Biosensors... 

Kuan SS, Guilbault GG. Ion selective electrodes and biosensors based on ISEs. In Turner APF, Karube I, Wilson GS, editors. Bioserisors, fundamentals and apphcations. Oxford Oxford University Press, 1987. 

Of the achievements of scientific research only those find industrial applications for which there is a demand and which are likely to provide reliable results under industrial conditions. In our opinion good new sensors and sensor arrays, like ISFETs and CHEMFETs, biosensors have great future prospects. Accordingly, remarkable efforts are being expended in sensor research and development. The wide range of compounds that can be measured with biosensors has been summarized by Mullen and Evans. Compounds that can be measured by electrochemical methods are listed in Table 1. There is a large volume of litterature on the combination of ion-selective electrodes and biosensors. 

Potcntiomctric Biosensors Potentiometric electrodes for the analysis of molecules of biochemical importance can be constructed in a fashion similar to that used for gas-sensing electrodes. The most common class of potentiometric biosensors are the so-called enzyme electrodes, in which an enzyme is trapped or immobilized at the surface of an ion-selective electrode. Reaction of the analyte with the enzyme produces a product whose concentration is monitored by the ion-selective electrode. Potentiometric biosensors have also been designed around other biologically active species, including antibodies, bacterial particles, tissue, and hormone receptors. 

For pesticide analysis, the potential of enzyme biosensors has been tested. In this field, biosensors based on the inhibition of acetylcholinesterases, acylcholinesterases, or butylrylchol-inesterases by organophosphorus compounds are widely used. Their specific activity can be monitored by electrochemical methods such as the ion-selective electrode and the ion-selective field effect transistor (ISFET). 

Lifetime. As already mentioned above, some rugged solid-state sensors have lifetimes of several years. Certain sensors can also be regenerated when their function begins to deteriorate. The shortest lifetimes are exhibited by biosensors. Ion-selective electrodes and optical sensors based on membrane-bound recognition molecules often lose their ability to function by a leaching-out effect. In optical sensors the photobleaching effect may also reduce the lifetime to less than a year. On the other hand, amperometric cells work well for many years, albeit with restricted selectivities. 

For the transducers, i.e., ion-selective electrodes and optical fiber, that do not perturb the concentration of the determining compound at the surface, the biosensor response R can be written as... 

Environmental Applications Although ion-selective electrodes find use in environmental analysis, their application is not as widespread as in clinical analysis. Standard methods have been developed for the analysis of CN , F , NH3, and in water and wastewater. Except for F , however, other analytical methods are considered superior. By incorporating the ion-selective electrode into a flow cell, the continuous monitoring of wastewater streams and other flow systems is possible. Such applications are limited, however, by the electrode s response to the analyte s activity, rather than its concentration. Considerable interest has been shown in the development of biosensors for the field screening and monitoring of environmental samples for a number of priority pollutants. 

The following set of suggested experiments describes the preparation of solid-state and liquid ion-exchange ion-selective electrodes, as well as potentiometric biosensors. 

There are also RMs which are prepared for a specific application and are used for validation of relevant methods. Cobbaert et al. (1999) made use of Ion Selective Electrode (ISE)-protein-based materials when evaluating a procedure which used an electrode with an enzyme-linked biosensor to determine glucose and lactate in blood. Chance et al. (1999) are involved with the diagnosis of inherited disorders in newborn children and they prepared a series of reference materials consisting of blood spotted onto filter paper and dried, from which amino-acids can be eluted and... 

The material is presented in 17 chapters, covering topics such as trends in ion selective electrodes, advances in electrochemical immunosensors, modem glucose biosensors for diabetes management, biosensors based on nanomaterials (e.g. nanotubes or nanocrystals), biosensors for nitric oxide and superoxide, or biosensors for pesticides. 

Composite potentiometric sensors involve systems based on ion-selective electrodes separated from the test solution by another membrane that either selectively separates a certain component of the analyte or modifies this component by a suitable reaction. This group includes gas probes, enzyme electrodes and other biosensors. Gas probes are discussed in this section and chapter 8 is devoted to potentiometric biosensors. 

Chapters 1 to 5 deal with ionophore-based potentiometric sensors or ion-selective electrodes (ISEs). Chapters 6 to 11 cover voltammetric sensors and biosensors and their various applications. The third section (Chapter 12) is dedicated to gas analysis. Chapters 13 to 17 deal with enzyme based sensors. Chapters 18 to 22 are dedicated to immuno-sensors and genosensors. Chapters 23 to 29 cover thick and thin film based sensors and the final section (Chapters 30 to 38) is focused on novel trends in electrochemical sensor technologies based on electronic tongues, micro and nanotechnologies, nanomaterials, etc. 

The potentiometric biosensor is a combination of an ion-selective electrode (ISE) base sensor with a vegetable tissue (the source of enzyme), which provides a highly selective and sensitive method for the determination of a given substrate. Advantages of such potentiometric biosensors are simplicity of instrumentation (only a pH meter is needed),... 

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