Entrapment within electrochemically

Equations (2.14) to (2.23) were obtained on the assumption that electroactive molecules are uniformly distributed in the entire volume of the solid. However, this is an unrealistic assumption in cases where bulky guest species are entrapped within the cavities of the porous material. Here, ship-in-a-bottle synthetic procedures most likely yield a nonuniform distribution of guest species in the network of the host porous material. Electrochemical data can then be used for obtaining information on the distribution of electroactive species. 

Aspects of loading with nonrigid films have been considered by several authors [18-22]. The primary case of interest in the electrochemical context is loading with a rigid layer (the elechode), a viscoelastic film (commonly, though not necessarily, a polymer), and then a Newtonian fluid, schematically illustrated in Fig. 3. (The rigid layer component may also include material entrapped within sm-face features [23].) The characteristic mechanical impedances of the two nonrigid... 

The main strategies employed for biomolecule immobilization by electropolymerized films encompass entrapment within the polymer during its electrochemical growth, covalent binding onto polymers and non-covalent binding by specific affinity, or host-guest interactions between films and biomolecules. 

Entrapment of Enzymes within Electrochemically-Grown Conducting Polymer Films... 

Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

Similarly to the above-mentioned entrapment of proteins by biomimetic routes, the sol-gel procedure is a useful method for the encapsulation of enzymes and other biological material due to the mild conditions required for the preparation of the silica networks [54,55]. The confinement of the enzyme in the pores of the silica matrix preserves its catalytic activity, since it prevents irreversible structural deformations in the biomolecule. The silica matrix may exert a protective effect against enzyme denaturation even under harsh conditions, as recently reported by Frenkel-Mullerad and Avnir [56] for physically trapped phosphatase enzymes within silica matrices (Figure 1.3). A wide number of organoalkoxy- and alkoxy-silanes have been employed for this purpose, as extensively reviewed by Gill and Ballesteros [57], and the resulting materials have been applied in the construction of optical and electrochemical biosensor devices. Optimization of the sol-gel process is required to prevent denaturation of encapsulated enzymes. Alcohol released during the... 

Immobilisation of biomolecules on the surface of an effective matrix with maximum retention of their biological recognition properties is a crucial problem for the commercial development of a biosensor. Different methods of immobilisation have been used. One such method is electrochemical entrapment. Several conducting polymers can be deposited electrochemically and, in the process, a biological molecule can be entrapped. This process is also useful in the fabrication of microsensors in preparation of a multilayered structure with one or more enzymes/biomolecules layered within a multilayered copolymer for analysis of multiple analytes [133-135]. A number of reports have appeared on immobilisation of biomolecules using electrochemical entrapment [130, 131, 136-143]. 

Other approaches that have been used for the immobilization of tissues for the construction of tissue-based biosensor include packing of tissues materials within the micropores of a porous carbon electrode, entrapment of tissue cells into electrochemically grown polymers, and incorporation into minireactors or column for flow analysis. 

A more typical situation is obtained with an ionic conductor which can be electrochemically reduced or oxidized. When it is inserted between two electrodes, both reactions can occur simultaneously oxidation at the anode and reduction at the cathode. According to our model the material can then be regarded as a double reservoir in which electrons can be stored at a certain level and holes at another, in two different parts of the material. The voltage of the corresponding cell simply equals the distance between the two levels to within the multiplication factor F 1 93, its electrical capacity is determined by the number of electrons and electron holes which can be entrapped. The electrode reactions occurring at che phase boundary of such a cell simply imply an injection or extraction of electronic carrier and no transfer of matter. This would certainly obviate many difficulties encountered in more traditional batteries. The validity of the principle was demonstrated in our laboratory with KI. The voltage obtained was approximately 1.3 V. For practical purposes the KI cell is obviously not of interest since its electrical capacity is too small. 

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