Immobilization of electroactive

There are three principal approaches used for the immobilization of electroactive substances onto surfaces chemisorption, covalent bonding, and film deposition. 

Pyrene- tetrathiafulvalene Formation of flexible and medium length chains Template for immobilization of electroactive unit on CNTs surface Ehli et al. (2008)... 

For application of protein-immobilized porous materials to sensor fields, use of an electroactive substance as the framework material is important. DeLouise and Miller demonstrated the immobilization of glutathione-S-transferase in electrochemically etched porous silicon films [134], which are attractive materials for the construction of biosensors and may also have utility for the production of immobilized enzyme bioreactors. Not limited to this case, practical applications of nanohybrids from biomolecules and mesoporous materials have been paid much attention. Examples of the application of such hybrids are summarized in a later section of this chapter. 

DENs can be immobilized on electroactive substrates to prepare heterogenized homogeneous catalysts. Electrochemical grafting of hydroxyl-terminated Pt DENs... 

The lure of new physical phenomena and new patterns of chemical reactivity has driven a tremendous surge in the study of nanoscale materials. This activity spans many areas of chemistry. In the specific field of electrochemistry, much of the activity has focused on several areas (a) electrocatalysis with nanoparticles (NPs) of metals supported on various substrates, for example, fuel-cell catalysts comprising Pt or Ag NPs supported on carbon [1,2], (b) the fundamental electrochemical behavior of NPs of noble metals, for example, quantized double-layer charging of thiol-capped Au NPs [3-5], (c) the electrochemical and photoelectrochemical behavior of semiconductor NPs [4, 6-8], and (d) biosensor applications of nanoparticles [9, 10]. These topics have received much attention, and relatively recent reviews of these areas are cited. Considerably less has been reported on the fundamental electrochemical behavior of electroactive NPs that do not fall within these categories. In particular, work is only beginning in the area of the electrochemistry of discrete, electroactive NPs. That is the topic of this review, which discusses the synthesis, interfacial immobilization and electrochemical behavior of electroactive NPs. The review is not intended to be an exhaustive treatment of the area, but rather to give a flavor of the types of systems that have been examined and the types of phenomena that can influence the electrochemical behavior of electroactive NPs. 

We turn now to discussion of the specific types of electroactive NPs that have been described. The NPs are grouped according to the composition of the electroactive NP rather than the method of immobilization. In most cases, metal-oxide/ hydroxide/oxyhy dr oxides materials are grouped together using a formulation such as MO , to indicate the different compositions and redox states of the metals that may be described. 

Electropolymerizable monomers that give rise to conducting electroactive polymers (CEPs) or insulating polymer thin films provide a convenient approach for the immobilization of DNA. More importantly, this method provides an easy means to achieve spatial separation of the ssDNA sequence... 

Principally, SSLEC cells may be constructed by inserting any electroactive and luminescent materials directly between electrodes or by their immobilization in more or less inert matrixes. The immobilization of the active material in an inert matrix exhibits several attractive features allowing the variation of the emitter concentration as well as tuning the system s properties by choosing different host materials. The highest possible emitter (polymeric materials or small molecules) concentration, however, can be achieved for the emissive layer with little amount (or even without) any host material. 

There are several reasons for the appeal of polymer modification immobilization is technically easier than working with monolayers the films are generally more stable and because of the multiple layers redox sites, the electrochemical responses are larger. Questions remain, however, as to how the electrochemical reaction of multimolecular layers of electroactive sites in a polymer matrix occur, e.g., mass transport and electron transfer processes by which the multilayers exchange electrons with the electrode and with reactive molecules in the contacting solution [9]. 

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]. 

The amperometric transduction of an immunoreaction consists in the post-labeling of the detected target by an enzyme able to catalyze the production or the consumption of electroactive species. The electrochemical oxidation or reduction of the latter at a constant potential applied to the immunosensor provides thus a current, whose intensity is proportional to the amount of immobilized target. 

Fig. 5 Reversible oxidation and reduction of electroactive SAMs to generate renewable microarray surfaces for bioanalysis left). Corresponding fluorescent micrographs (right) depicting three cycles of carbohydrate and protein immobilization and release on the same substrate...

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