Chemical modification of electrode surfaces

Chemical modification of electrode surfaces by polymer films offers the advantages of inherent chemical and physical stability, incorporation of large numbers of electroactive sites, and relatively facile electron transport across the film. Since th% polymer films usually contain the equivalent of one to more than 10 monolayers of electroactive sites, the resulting electrochemical responses are generally larger and thus more easily observed than those of immobilized monomolecular layers. Also, the concentration of sites in the film can be as high as 5 mol/L and may influence the reactivity of the sites because their solvent and ionic environments differ considerably from dilute homogeneous solutions [9]. 

Electrode modification by the attachment of various types of biocomponents holds considerable promise as a novel approach for electrochemical (potentiometric, conductometric, and amperometric) biosensors. Potentiometric sensors based on coupled biochemical processes have already demonstrated considerable analytical success [26,27]. More recently, amperometric biosensors have received increasing attention [27,28] partially as a result of advances made in the chemical modification of electrode surfaces. Systems based on... 

As shown in this symposium, interest in chemical modification of electrode surfaces has been extended in many directions, including the study of light-assisted redox reactions, and the use of modified electrodes in electrochromic devices (1,2). Our own studies have centered on the study of metal and metal oxide electrodes modified with very thin films of phthalocyanines (PC) and on the electrochromic reaction of n-heptyl viologen on metal oxide electrodes, and on the effect on these reactions of changing substrate chemical and physical composition (A,5). 

Since the pioneering work of Updike and Hicks in developing enzyme electrodes and Lane and Hubbard in direct chemical modification of electrode surfaces, a great deal of attention has been paid to developing chemically modified electrodes. The result is that virtually every substance that is electroactive, or for which its chemical reaction can be coupled to the electrode-modifying matrix and/or electron transfer mediator, can now be detected electrocheniically. Principles, techniques, and scope of application of CMEs as sensors in analytical... 

The reality is that surface electrode modification is needed to make the ultramicroelectrode material selective for NO. Therefore, the design of modified electrode surfaces using organized layers is very attractive and provides the ideal strategy. In the general case, the chemical modification of electrode surfaces with polyelectrolytes and metal complex-based polymer films has expanded the scope of appUcation of such designed electrodes and provided a lot of options for then-use in various experimental conditions. In addition to their electrocatalytic applications, such electrodes showed a great promise for electroanalysis. As far as this aspect is concerned, substantial improvements in selectivity, sensitivity, versatiUty and reproducibility can be achieved. 

Formation of monolayers by self-assembly at electrode surfaces has been widely used in recent years. How to bind molecules on electrode surfaces has been studied extensively among electrochemists since mid-1970s, and is called chemical modification of electrode surfaces [283-285]. More recently, chemisorbed ordered organic monolayers on gold, silver, and oxides have been studied extensively and are called sdfassemhled monolayers (SAMs) [286-289]. SAMs are... 

Gorton and coworkers have been particularly active in this field and produced an excellent review of the methods and approaches used for the successful chemical modification of electrodes for NADH oxidation [33]. They concentrated mainly on the adsorption onto electrode surfaces of mediators which are known to oxidise NADH in solution. The resulting systems were based on phenazines [34], phenoxazines [35, 36] and pheno-thiazines [32]. To date, this approach has produced some of the most successful electrodes for NADH oxidation. However, attempts to use similar mediators attached to poly(siloxane) films at electrode surfaces have proved less successful. Kinetic analysis of the results indicates that this is because of the slow charge transfer between the redox centres within the film so that the catalytic oxidation of NADH is restricted to a thin layer nearest the electrode surface [37, 38]. This illustrates the importance of a charge transfer between mediator groups in polymer modified electrodes. 

Additives have been routinely used in corrosion catalysis and electrodeposition (3,A),flelds In which metals Interface with electrolytic solutions. Studies In these areas are part of the field of modification of metal surfaces In order to change the rates of processes occurring at the surface. In recent years there has been a good deal of work on what Is known as chemical modifications of electrodes (. While these semipermanent modifications have Involved seme sophisticated Investigations, the additive field Is largely studied by a trial and error process. The work In our laboratories has been aimed at obtaining an understanding of the role of additives In these... 

An electrochemical OP sensor by the nonenzymatic route was reported based on chemical modification of the surface of a gold electrode with ferrocene derivative (Fc). For this purpose, the gold electrode was modified with dithioFc derivative to form an aminoFc-monolayer-modified electrode (Khan et al, 2007). The principle of operation of the aminoFc-modified electrode for OP sensing is that chloro-or cyano-substitued OP compounds covalently bind to aminoFc moieties, by which the redox potential of the surface-confined Fc can be altered. In fact, ca. 110 and 60 mV shifts in the redox potential were observed, suggesting a possible use of the sensors for detecting OPs from the potential shifts. 

Market and business issues have also slowed chemical sensor and biosensor commercialization. As often occurs with technologies encompassing many disciplines, problems with patents and proprietary technology protection have appeared. For example, one common transducer used for both chemical sensors and biosensors is the integrated electrode capacitor (see chapter 8 for a description of this transducer). Although the design for this transducer has been in the public domain for over 25 years, chemical modification of the surface characteristics of the electrodes can lead to a new patent position. This then leads to complex claims and counterclaims about the use of the basic transducer technology. 

The modification of electrode surfaces with polymer films has received considerable attention because of many advantageous properties of polymers (2,3). Polymer films are chemically stable, provide diffusional barriers that can lead to selectivity based on size or charge exclusion properties, provide a means of preconcentrating analytes by ionic or other complexation interactions, and are a convenient matrix for the immobilization of other reagents, such as enzymes. Coating electrode surfaces with polymer films takes advantage of these properties. Complexation of a specific... 

Treelike molecules are attracting increasing attention because of their unique structure and properties. Since the first report on dendrimers has been given by F. Vogtie and co-workers [1] in 1978, several synthetic pathways to dendrimers have been developed and a number of core molecules and monomers have been used to prepare different dendrimers [2]. The surface of dendrimers can be modified with many organotransition-metal complex fragments. Ferrocenyl-based dendrimers can be used in the chemical modification of electrodes, in the construction of amperometric biosensors or as multi-electron reservoirs [3]. 

The behavior of interfacial water molecules on platinmn single-crystal electrodes, under electrochemical conditions, has been characterized for the first time by means of the laser-induced temperature jump method. The fundamentals of this method and the proposed interpretation of the experimental results will be described in Section V.l and V.2. Then, recent results on the three platinum basal planes will be discussed in Section V.3. Afterwards, the application of this technique to Pt(lll) stepped surfaces will be explained in Section V.4. And finally, results on the effect of the chemical modification of the surface composition of Pt(l 11) by adatom deposition will be presented in Section V.5. 

He has pubhshed approximately 50 papers in international peer-reviewed journals and two book chapters. Dr. Terzi has been invited to hold seminars and to be Guest Editor for special issues of international journals. He visited the Laboratory of Materials Chemistry and Chemical Analysis (University of Turku, Finland) and the Department of Chemistry (University of Oxford, UK) in order to broaden his knowledge on surface characterization techniques. His main scientific interests are (i) the modification of electrode surfaces using conducting polymers, self-assembled monolayers, (nano)particles, and graphene (ii) the spectroscopic and microscopic characterization of the electrode coatings (iii) the synthesis and characterization of (nano)particles (iv) electrocatalysis applied to amperometric sensors. 

Chemical modification of diamond surfaces is a ripe area for research. Much can be learned about (1) how to control the electrode reaction kinetics and mechanisms at diamond through alterations of the surface chemistry and (2) using such modified surfaces as platforms for sensors and other devices based on the material. 

Since the nature and acidity of EGA are different from that of the conventitMial chemical acids, it is expected that EGA promotes the already known acid-catalyzed reactions more effectively with high product selectivity and, moreover, unprecedented reactions can be realized by EGA. In addition to the application of EGA to organic synthesis, the modification of electrode surface with EGA seems to grow up to be a promising area. 

Reaction control is very important in electrosynthetic chemistry. Because electron transfer takes place on electrode surface and/or vicinity, that is, electrode interface, the chemical functionality-modification of electrode surface has been intensively studied for this purpose so far [1]. On the other hand, mechanical energies such as ultrasound and centrifugal force cannot drive chemical reactifflis but control them. From this point of view, the mechanical energy modification of electrode interface has been also developed for the reaction control of electrosynthetic processes especially in the last two decades [2,3]. 

Many different procedures for modification of electrode surfaces by zeolites have been proposed (106). In practice, fabrication of zeolite modified electrodes is complicated by at least two factors first, zeolites are electrically insulating, and second, immobilization of the film by physical or chemical bonding is difficult. Most successful zeolite modification schemes employ composites, where polymers or conductive powders are used as a matrix to support the zeolite. In any successful scheme, electroactive analyte molecules and counter-ions must be able to undergo rapid mass transport within the zeolite-based film. 

Surface mobility of adsorbed hydrogen in the catalytic layer favors proton migration between membrane and electrodes and improves Pt utilization. Mobility is usually associated with proton acceptor groups in the vicinity of catalyst nanoparticles. The chemical modification of the surface of carbon supports with proton acceptors has been proposed as a promising strategy to improve the catalytic layer performance [1-4]. 

Modification of electrode surfaces with polymer is seeking the same objective as with monolayers, i.e., the improvement of the analytical performances in terms of selectivity and sensitivity. These improved performances can be achieved by the nature of the polymer itself (e.g., perfluorinated cation-exchanger Nafion ) or by the incorporation of chemical functionalities. Recognition elements (e.g., biomolecules, ligands) can be entrapped during the polymerization process (electro- or photopolymerization) or attached after polymerization by chemical grafting or by... 

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