Chemically modified electrode sensors

DURST AND BLUBAUGH Chemically Modified Electrode Sensors... 

Durst, R. A. "Chemically Modified Electrode Sensors for Biocomponents," Presented at the Fourth Scientific Session on Ion-Selective Electrodes, Matrafilred, Hungary, October 10, 1984. 

Carballo, R., V.C. DaH Orto, A. Lo Balbo, and I. Rezzano (2003). Determination of sulfite by flow injection analysis using poly[Ni-(protoporphyrin DC)] chemically modified electrode. Sensor Actuators B Chem. 88,155-161. 

Durst, R.A. and Blubaugh, E.A. (1986) Chemically modified electrode sensors. ACS Symp. Ser. (Fundam. Appl Chem. Sens.), 309, 245-255. 

The historical development of chemically electrodes is briefly outlined. Following recent trends, the manufacturing of modified electrodes is reviewed with emphasis on the more recent methods of electrochemical polymerization and on new ion exchanging materials. Surface derivatized electrodes are not treated in detail. The catalysis of electrochemical reactions is treated from the view of theory and of practical application. Promising experimental results are given in detail. Finally, recent advances of chemically modified electrodes in sensor techniques and in the construction of molecular electronics are given. 

J. Pei and X. Li, Amperometric glucose enzyme sensor prepared by immobilizing glucose oxidase on CuPtC16 chemically modified electrode. Electroanalysis 11, 1266-1272 (1999). 

R.M. Ianniello and A.M. Yacynych, Immobilized enzyme chemically modified electrode as an amperometric sensor. Anal. Chem. 53, 2090-2095 (1981). 

J.H. Pei and X.Y. Li, Xanthine and hypoxanthine sensors based on xanthine oxidase immobilized on a CuPtCl6 chemically modified electrode and liquid chromatography electrochemical detection. Anal. Chim. Acta 414, 205-213 (2000). 

Figure 3.12 — Interfacing of a fermenter to an FI system. The fermenter medium is continuously recycled by a pump to the filter unit, from which the filtrate is guided to a small reservoir (500 /xL). The sample solution is aspirated through a dialyser, the acceptor stream of which is fed to the injector of the FIA system. The analyte content is assayed amperometrically by using the glucose sensor incorporating the enzyme-containing chemically modified electrode. (Reproduced from [86] with permission of Elsevier Science Publishers).

One of the goals in the chemically modified electrode research area has been to develop new types of electrochemical sensors. Several review articles have recently been published on this subject [86,87], Our intent is not to provide another review of this voluminous literature. Rather, we would like to introduce the reader to the concepts behind the use of chemically modified electrodes as electrochemical sensors. As we will see, the key to developing new sensors is... 

We begin by pointing out that this concept of covering an electrode surface with a chemically selective layer predates chemically modified electrodes. For example, an electrode of this type, the Clark electrode for determination of 02, has been available commercially for about 30 years. The chemically selective layer in this sensor is simply a Teflon-type membrane. Such membranes will only transport small, nonpolar molecules. Since 02 is such a molecule, it is transported to an internal electrolyte solution where it is electrochemically reduced. The resulting current is proportional to the concentration of 02 in the contacting solution phase. Other small nonpolar molecules present in the solution phase (e.g., N2) are not electroactive. Hence, this device is quite selective. 

Glucose sensors based on this electrochemistry are now commercially available. Furthermore, it seems likely that this concept will soon be expanded to other types of enzyme-based sensors. Hence, sensor development is proving to be one of the great success stories of the chemically modified electrode research area. 

Electroanalytical sensors based on amperometric measurements at chemically modified electrodes are in the early stages of development. The modes of modification can take many forms, but the most common approach at the present time is the immobilization of ions and molecules in polymer films which are applied to bare metal, semiconductor, and carbon electrodes. Such surface-modified electrodes exhibit unique electrochemical behavior which has been exploited for a variety of applications. 

Gorton, L, Bremle, G., Gsoregi, E., Jdnsson-Pettersson, G., and Persson, B. (1991) Amperometric glucose sensors based on immobilized glucose-oxidizing enzymes and chemically modified electrodes. Analytica Chimica Acta, 249, 43-54. 

Mediator-chemically modified electrodes have been coupled either with ADH membranes to give enzyme electrodes (Cenas et al. 1984) or with ADH reactors, e.g., in an FIA device (Huck et al. 1984). Quinoidic groups, Meldola s Blue, and Nile Blue have been used as mediators. Albery et al. (1987b) employed an electrode containing NMP+ and TCNQ" in a PVC carrier for NADH oxidation. ADH was entrapped on the sensor surface by a dialysis membrane. 

In this chapter, we discuss voltammetric methods and associated electrochemical sensors, including chemically modified electrodes. Voltammetric techniques use a microelectrode for microelectrolysis. Here, the potential is scanned and a dilute solution of the analyte produces, at a given potential, a limiting current (microampere range or less), which is proportional to the analyte concentration. Am-perometry is the application of voltammetry at a fixed potential to follow, via the current, changes in concentration of a given species, for example, during a titration. Amperometric measurements also form the bases of electrochemical sensors. 

Amperometric electrodes are a type of electrochemical sensor, as are potentiometric electrodes discussed in Chapter 13. In recent years there has been a great deal of interest in the developmenfoTv ious types of electrochemical sensors that exhibit increased selectivity or sensitivity. These enhanced measurement capabilities of amperometric sensors are achieved by chemical modification of the electrode surface to produce chemically modified electrodes (CMEs). 

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