Electrodes bioelectrocatalytic

Morozov SV, Vignais PM, Coumac L, Zorin NA, Karyakina EE, Karyakin AA, Cosnier S. 2002. Bioelectrocatalytic hydrogen production by hydrogenase electrodes. Int J Hydrogen Energy 27 1501 -1505. 

Moreover, it has been demonstrated that CNTs promote the direct electrochemistry of enzymes. Dong and coworkers have reported the direct electrochemistry of microperoxidase 11 (MP-11) using CNT-modified GC electrodes [101] and layer-by-layer self-assembled films of chitosan and CNTs [102], The immobilized MP-11 has retained its bioelectrocatalytic activity for the reduction of H202 and 02, which can be used in biosensors or biofuel cells. The direct electrochemistry of catalase at the CNT-modified gold and GC electrodes has also been reported [103-104], The electron transfer rate involving the heme Fe(III)/Fe(II) redox couple for catalase on the CNT-modified electrode is much faster than that on an unmodified electrode or other... 

S.M. Chen and S.V. Chen, The bioelectrocatalytic properties of cytochrome c by direct electrochemistry on DNA film modified electrode. Electrochim. Acta 48, 513-529 (2003). 

In DET, the enzymatic and electrode reactions are coupled by direct (mediatorless) electron transfer. In this case, the electron is transferred directly from the electrode to the substrate molecule (or vice versa) via the active site of the enzyme. In such a system, the coupled overall process is the redox transformation of the substrate(s), which can be considered as an enzyme-catalyzed electrode process. According to this mechanism, the electrode surface acts as the enzyme cosubstrate, and the enzymatic and electrode reactions cannot be considered as separate, but as formal stages of the bioelectrocatalytic reaction mechanism. The catalytic effect of the enzyme is the... 

Metallic nanoparticles and single-walled carbon nanotubes (SWCNTs) exhibit nanoscale dimensions comparable with the dimensions of redox proteins. This enables the construction of NP-enzyme or SWCNT-enzyme hybrids that combine the unique conductivity features of the nanoelements with the biocatalytic redox properties of the enzymes, to yield wired bioelectrocatalyts with large electrode surface areas. Indeed, substantial advances in nanobiotechnology were achieved by the integration of redox enzymes with nanoelements and the use of the hybrid systems in different bioelectronic devices.35... 

A further approach to electrically wire redox enzymes by means of supramolecular structures that include CNTs as conductive elements involved the wrapping of CNTs with water-soluble polymers, for example, polyethylene imine or polyacrylic acid.54 The polymer coating enhanced the solubility of the CNTs in aqueous media, and facilitated the covalent linkage of the enzymes to the functionalized CNTs (Fig. 12.9c). The polyethylene imine-coated CNTs were covalently modified with electroactive ferrocene units, and the enzyme glucose oxidase (GOx) was covalently linked to the polymer coating. The ferrocene relay units were electrically contacted with the electrode by means of the CNTs, and the oxidized relay mediated the electron transfer from the enzyme-active center to the electrode, a process that activated the bioelectrocatalytic functions of GOx. Similar results were observed upon tethering the ferrocene units to polyacrylic acid-coated CNTs, and the covalent attachment of GOx to the modifying polymer. 

Several electrical aptamer biosensors implemented the biocatalytic hydrolytic activities of thrombin, or the fact that proteins (e.g., thrombin) often include several binding sites for the formation of supramolecular complexes with different aptamers. The bioelectrocatalytic detection of thrombin by an electrical aptasensor was demonstrated by formation of an aptamer-thrombin complex on the electrode, followed by a thrombin-mediated hydrolysis of the nitroaniline-functionalized peptide, (22), yielding the redox-active product nitroaniline, (23), which was analyzed electrochemically76 (Fig. 12.20b). A further bioelectrocatalytic aptasensors configuration is depicted in Fig. 12.20c, where the multidentate formation of aptamer-protein supramolecular complexes was used to analyze thrombin.76 Thrombin includes two different binding sites for aptamers.77 One of the thrombin aptamers... 

Scheme 8 Assembly of a photoisomerizable glucose oxidase monolayer electrode and the reversible photoswitchable activa-tion/deactivation of the bioelectrocatalytic functions of the enzyme electrode.

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... 

Raitman OA, Katz E, Biickmann AF et al (2002) Integration of polyaniline/poly(acrylic acid) films and redox enzymes on electrode supports an in situ electrochemical/surface plasmon resonance study of the bioelectrocatalyzed oxidation of glucose or lactate in the integrated bioelectrocatalytic systems. J Am Chem Soc 124 6487-6496... 

Sensors have also been constructed from some oxidases directly contacted to electrodes to give bioelectrocatalytic systems. These enzymes utilize molecular oxygen as the electron acceptor for the oxidation of their substrates. Enzymes such as catechol oxidase, amino acid oxidase, glucose oxidase, lactate oxidase, pyruvate oxidase, alcohol oxidase, xanthine oxidase and cholesterol oxidase catalyze the oxidation of their respective substrates with the concomitant reduction of O2 to H2O2 ... 

Many examples of polymer-embedded enzyme bioelectrocatalytic electrodes exist [91-93]. The electrical contacting of enzymes immobilized in polymer matrices is achieved either by virtue of a conducting polymer, or by incorporating electron relay groups within the polymer, providing electron hopping between the enzyme and the electrode support. 

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