In modified electrodes

Organic polymers are widely used in modified electrodes [220], but inorganic materials such as zeoHtes, clays or microporous solids are attractive as replacements since they have much better stability, tolerance to high temperatures and oxidizing conditions, and chemical inertness. Due to the capability of clays to exchange intercalated ions, clay modified electrodes have been extensively studied. 

Bmening, M.L. and Rnsling, J. (2006) in Modified Electrodes. Encyclopedia of Electrochemistry Vol. 10 Synthesis of Layered Polyelectrolyte Films (eds A.J. Bard, M. Stratmann, M. Fujihira, J.F. Rnsling and I. Rubinstein), Wdey-VCH, Weinheim. 

Since the pioneering work of Lane and Hubbard, there have been numerous examples of using chemisorption to modify electrode surfaces. For example, Anson and his coworkers have investigated chemisorption of various aromatic systems onto carbon electrodes [12]. In this case, n-electron density is shared between the electrode and the adsorbate molecule. Examples of electroactive molecules that have been used to modify electrode surfaces via this approach are shown in Table 13.1 [8]. It is of interest to note that from the very beginning, there was considerable interest in modifying electrode surfaces with biochemical substances (Table 13.1). This is because such modified electrodes seemed to be likely candidates for use in electrocatalytic processes and biochemical sensors (see Section V). 

Figure 5.69 The different reaction layers that are possible in the analysis of the mediation process in modified electrodes, together with the notations which relate to the rate-determining steps in each case (see text for further details). Hatched region is the electrode. The black section the reaction layer...

TABLE 14.4.1 Expressions for Plateau Currents in Koutecky-Levich Format for Various Dynamical Cases in Modified Electrode Systems"... 

The capacity to preconcentrate anions has enabled the use of chitosan and its derivatives in modified electrodes, for application in sensor and biosensor electrochemistry [233]. To facilitate improving water solubility of biologically useful chitosan derivatives, N-methylene phosphonic chitosan has been prepared using a one-step reaction that allowed homogeneous modifications [234]. 

Clearly ellipsometry has much to reconunend it for studies in modified electrodes however until recently its application to electrochemical problems was restricted by several severe problems. Firstly it is not mathematically straightforward to extract optical data from parameters measured by ellipsometers. Secondly collecting each data point used to involve tedious and slow manual determination. In the last 15 years however, two developments have overcome these problems the development of inexpensive microcomputers and automation of the data collection process. The only drawback now remaining is the capital cost of suitable equipment, and even this is declining rapidly as new and simpler types of ellipsometer become available. 

Albeiy W., Chen Z., Horrocks B., Mount A., Wilson R, Bloor D., Monkman A, and Elliott C., Spectroscopic and electrochemical studies of charge transfer in modified electrodes, Faraday discuss, Chem. Soc., 1989,88, 247-259. 

Araki, K., L. Angnes, C.M.N. Azevedo, and H.E. Toma (1995). Electrochemistry of a tetraruthenated cobalt porphyrin and its use in modified electrodes as sensors of reducing analytes. J. Electroanal. Chem. 397, 205-210. 

In this chapter, we describe the recent trends in the field of electrochemical biodevices exploring the principal strategies utilized in the last years to improve signal response of enzymatic biocatalysis and describe briefly the electrochemical characteristics of several nanomaterials when utilized in modified electrodes. The fabrication of nanoelectrodes by some techniques is also explored in this chapter. In addition, we will discuss the many efforts in order to detect specific molecules in vitro and in vivo and recent advances in the development of implantable biosensors. 

To be employed as a chemical sensor the CME must be capable of producing an electrical signal which is related to the concentration of the analyte. (An excellent study of the mechanism of electrode transport in modified electrodes... 

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