Electrical communication between

Describe various routes for facilitating the electrical communication between the redox center of glucose oxidase and an electrode surface. 

Gap junctions provide electrical communication between cells, forming a functional syncytium Myogenic... 

Skeletal and cardiac muscles also have important differences. Skeletal muscle cells are elongated and run the length of the entire muscle furthermore, these cells have no electrical communication between them. Cardiac muscle cells, on the other hand, branch and interconnect with each other. Intercellular junctions found where adjoining cells meet end-to-end are referred to as intercalated discs. Two types of cell-to-cell junctions exist within these discs. Desmosomes hold the muscle cells together and provide the structural support needed when the heart beats and exerts a mechanical... 

Y. Degani and A. Heller, Direct electrical communication between chemically modified enzymes and metal electrodes. I. Electron transfer from glucose oxidase to metal electrodes via electron relays, bound covalently to the enzyme. J. Phys. Chem. 91, 1285-1289 (1987). 

The electron-transfer rate between large redox protein and electrode surface is usually prohibitively slow, which is the major barricade of the electrochemical system. The way to achieve efficient electrical communication between redox protein and electrode has been among the most challenging objects in the field of bioelectrochemistry. In summary, two ways have been proposed. One is based on the so-called electrochemical mediators, both natural enzyme substrates and products, and artificial redox mediators, mostly dye molecules and conducted polymers. The other approach is based on the direct electron transfer of protein. With its inherited simplicity in either theoretical calculations or practical applications, the latter has received far greater interest despite its limited applications at the present stage. 

Figure 3.15 [63]. The table in Figure 3.15 also shows enhanced electron transfer rates for ferrocene attatched on aligned SWNTs as compared to ferrocene attatched on randomly dispersed SWNTs [124]. Moreover, such vertically aligned SWNTs act as molecular wires that allow efficient electrical communication between the underlying electrode and the redox enzymes [45, 123, 127[.

Enzyme biocatalyst assemblies on electrode surfaces usually do not achieve significant electron-transfer communication between the redox center and the conductive support, mostly because of the electrical insulation of the biocatalytic site by the surrounding protein matrixes. During the past four decades, several methods have been proposed and investigated in the field of bioelectrochemical technology in an effort to establish efficient electrical communication between biocatalysts and electrodes. " In general, electron transfer is classified by two different mechanisms (see Figure 2) ... 

Beny JL, Pacicca C Bidirectional electrical communication between smooth muscle and endothelial cells in the pig coronary artery. Am J Physiol 1994 266 H1465-H1472. 

Willner and coworkers have extended this approach to electron relay systems where core-based materials facilitate the electron transfer from redox enzymes in the bulk solution to the electrode.56 Enzymes usually lack direct electrical communication with electrodes due to the fact that the active centers of enzymes are surrounded by a thick insulating protein shell that blocks electron transfer. Metallic NPs act as electron mediators or wires that enhance electrical communication between enzyme and electrode due to their inherent conductive properties.47 Bridging redox enzymes with electrodes by electron relay systems provides enzyme electrode hybrid systems that have bioelectronic applications, such as biosensors and biofuel cell elements.57... 

For example, Willner and co-workers accomplished electrical communication between glucose oxidase (GOx) and a gold electrode using molecular-level assembly.5,6 Unprecedentedly effective electron transfer was observed from the FAD moiety to the electrode through the Au-nano particles (electron transfer turnover rate, 4500 s-1), derived from molecular conjugation and bioconjugation. 

A further approach to controlling electrical communication between redox proteins and their electrode support through a photo-command interface includes photo stimulated electrostatic control over the electrical contact between the redox enzyme and the electrode in the presence of a diffusional electron mediator (Scheme 12).[58] A mixed monolayer, consisting of the photoisomerizable thiolated nitrospiropyran units 30 and the semi-synthetic FAD cofactor 25, was assembled on an Au electrode. Apo-glucose oxidase was reconstituted onto the surface FAD sites to yield an aligned enzyme-layered electrode. The surface-reconstituted enzyme (2 x 10-12 mole cm-2) by itself lacked electrical communication with the electrode. In the presence of the positively charged, protonated diffusional electron mediator l-[l-(dimethylamino)ethyl]ferrocene 29, however, the bioelectrocatalytic functions of the enzyme-layered electrode could be activated and controlled by the photoisomerizable component co-immobilized in the monolayer assembly (Figure 12). In the... 

Parallel elongate cavities 13 and a layer of optical isolating material 18, surrounding each of the cavities, are formed within a substrate 10 of CdTe. The cavities each have a vertical wall 15 and a pyramidal floor 16. The wall and floor of each cavity has a body of detector material, HgCdTe, formed as a layer thereon. The body of detector material is comprised of a layer of a first type 22 and a layer of a second type 24. Individual electrical contacts 28 and a common electrical contact 29 are provided. An insulating layer 32 insulates the common contact from the substrate. A diffusion layer 34 of semiconductor material of the second type provides electrical communication between the common contact and the material of the second type formed in the cavity. The cavities may have cylindrical walls and a round floor. 

A buffer board is introduced in WO-A-8807764 which facilitates electrical communication between the detector elements and the module and conductive patterns formed on the module layers, and also enhances the structural characteristics and separate testability of the system components. 

One problem which arises when a detector array is attached to the face of a multi-layer module is the inability of the detector material to absorb forces generated by a mismatch of coefficient of thermal expansion between the detector array material and the module. Furthermore, it is difficult to isolate a fault that may be attributable to either the detector elements, module wiring or processing elements. A buffer board is introduced in WO-A-8807764 (Grumman Aerospace Corporation, USA, 06.10.88) which facilitates electrical communication between the detector elements and the module and conductive patterns formed on the module layers, and also enhances the structural characteristics and separate testability of the system components. 

Acetylcholineesterase and choline oxidase Au foil was treated with cystamine to produce a base layer of ami-nothiolate units, was derivatized by reaction of the amino group and disodium-4,4 -diisothiocyanato-trans-stilbene-2,2 -disulfonate. Enzymes were immobilized at the isothiocyanate group via thiourea link. The bifunctional sensor for ACh was prepared by stepwise immobilization of four layers of the enzyme ChO and three layers of AChE. Choline generated was detected amperometircally with the use of 2,6-dichloro-phenolindophenol as a mediator in solution. Electrical communication between the enzyme and the electrode is achieved either by the use of ferrocenecar-boxylic acid as mediator in the assay buffer or by immobilization of [(ferrocenyl methyl)amino] hexa-noic acid on the enzyme layer. [92]... 

The third generation of enzyme electrodes uses direct electrical communication between the redox centers of the enzymes and the electrode surface. This con-... 

Direct electrical communication between enzyme aetive sites and electrodes may also be facilitated by the nanoscale morphology of the electrode. The modification of electrodes with metal nanoparticles allows the tailoring of surfaees with features that can penetrate close enough to the enzyme aetive site to make non-mediated electron transfer possible. Electrodes modified by unaggregated 12 nm diameter gold nanoparticles have been found to have the eorrect morphology to allow direct electron transfer between the cytochrome c active site and the eleetrode [41]. Elec-... 

The chemical modification of redox enzymes with electron relay groups permits the mediated electron transfer and the electrical wiring of the proteins [83-85] (Figure 5A). The covalent attachment of electron-relay units at the protein periphery, as well as inner sites, yields short inter-relay electron-transfer distances. Electron hopping or tunneling between the periphery and the active site allows electrical communication between the redox enzyme and its environment. The simplest systems of this kind involve electron relay-functionalized enzymes diffusionally communicating with electrodes [83], but more complex assemblies including immobilized enzymes have also been reported. 

Photoswitchable electrical communication between enzymes and electrodes has also been achieved by the application of photoisomerizable electron-transfer mediators [195, 199]. DilTusional electron mediators (viologen or ferrocene derivatives) were functionalized with photoisomerizable spiropyran/merocyanine units. These mediators can be reversibly photoisomerized from the spiropyran state to the merocyanine state (360 < A < 380 nm) and back (A > 475 nm). An enzyme multilayer array composed of glutathione reductase or glucose oxidase was electrically contacted only when the photoactive group linked to the redox relay (viologen or ferrocene derivative, respectively) was in the spiropyran state. 

Figure 39. Electrical communication between an enzyme redox center and a photoexcited species attaining light-induced biocatalyzed transformations (A) direct electrical wiring of the protein by its chemical modification with tethered electron-relay units (B) electrical communication by the immobilization of the protein into a redox-functionalized polymer matrix.

All these bioelectrocatalytic functions of redox proteins are based on the control and enhancement of the electrical communication between the redox sites of the proteins and the electrode support. This is accomplished by the nano-engineering of the surfaces with covalently anchored proteins, the structural aligmnent of the proteins on the electrodes and the chemical modification of the proteins with redox-active units. Preliminary results suggest that two approaches will play important roles in the future development of bioelectronic systems (i) protein mutagenesis with specific functional amino acid residues that can align the protein on the electrode surface and control the electrical contact with the electrode (ii) the synthesis of de novo proteins with tailored bioelectronic and electrobiocatalytic functions. 

Redox-proteins usually lack direct electrical contact with electrodes because the redox site is embedded in the protein. This situation insulates the electrical communication between the redox-site and the electrode by the spatial separation of the protein redox-site from the electrode support. Suitable func-... 

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