Direct electron transfer of enzymes

Biosensors based on direct electron transfer of enzymes... 

Figure 14. Scheme of the different steps involved in the fabrication of aligned shortened SWCNT arrays for direct electron transfer of enzymes such as microperoxidase MP-11. From reference 92. 

Figure 6.7 illustrates the voltammetric response of the third-generation SOD-based 02 biosensors with Cu, Zn-SOD confined onto cystein-modified Au electrode as an example. The presence of 02" in solution essentially increases both the cathodic and anodic peak currents of the SOD compared with its absence [150], Such a redox response was not observed at the bare Au or cysteine-modified Au electrodes in the presence of 02". The observed increase in the anodic and cathodic current response of the Cu, Zn-SOD/cysteine-modified Au electrode in the presence of 02 can be considered to result from the oxidation and reduction of 02, respectively, which are effectively mediated by the SOD confined on the electrode as shown in Scheme 3. Such a bi-directional electromediation (electrocatalysis) by the SOD/cysteine-modified Au electrode is essentially based on the inherent specificity of SOD for the dismutation of 02", i.e. SOD catalyzes both the reduction of 02 to H202 and the oxidation to 02 via a redox cycle of its Cu (II/I) complex moiety as well as the direct electron transfer of SOD realized at the cysteine-modified Au electrode. Thus, this coupling between the electrode and enzyme reactions of SOD could facilitate the development of the third-generation biosensor for 02". ...

Direct electron transfer of proteins and enzymes on carbon nanotube electrodes... 

Direct electron transfer of other active enzymes... 

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. 

The enzyme-based biosensor has come through three steps (1) with oxygen for the media (2) with artificial intermediate for media and (3) without media and based for the direct electron transfer of redox proteins. The following is an example ... 

The ability of these enzymes to contact directly the electrode is attributed to the peripheral location of the redox center. A detailed kinetic study [11] of the peroxidase-catalyzed reduction of H2O2 revealed that 42 % of the enzyme molecules are aligned on the electrode surface in a configuration where the redox heme site is accessible for direct electron transfer. Other enzymes possess two redox sites, and electron transfer proceeds vectorially from a peripheral site to an inner component. For example, /7-cresol methyl hydroxylase [PCMH, a flavin adenine dinucleotide (FAD)- and heme-containing redox enzyme] affects the direct oxidation of p-cresol to -hydroxybenzaldehyde [12[ ... 

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