Enzymatic redox polymer-mediated

Subsequent research on osmium-modified polymers has shown how the redox potential can be controlled by altering bipyridine ligands of the immobilized osmium complexes. The ability to reliably modulate redox potential has significantly broadened the range of enzymes with which osmium redox polymer are compatible and allows for mediation of oxidative enzymatic reactions as well as reductive enzymatic reactions. 

A general problem of the potentiometric measurement is the low exchange current density of enzymatic substrate redox couples. Therefore additional mediators have to be applied with a high exchange current densitiy and fast electrode kinetics, which can react with the enzymatic products. Most often, these mediators are soluble low molecular weight substances, e.g. hexacyanoferrate. Until now, redox polymers based containing covalently bound osmium complexes [5 ] were only used in combination with oxidases for amperometric sensors. We could show that this redox polymer (E =... 

The potentiostatic multi-pulse potentiometry described here allows the dynamic measurement of potentials. The advantages of this method are the short time required for the analysis and the low noise of the signal. The "ancestor" of this technique, enzyme chronopotentiometry [7 ], posed problems of reproducibility when it was applied to the immobilized redox polymer. The excellent reproducibility of our method is clearly shown in fig. 3b. These techniques were the fundamental developments to conceive redox-FETs for the first time. After immobilization of NAD -dependent dehydrogenases covalently on the surface of the transducer the enzymatically produced NADH would be catalytically oxidized in situ by the polymeric mediator. To this very compact combination the substrate and NAD+ as cosubstrate have to be applied externally. The coimmobilization of the coenzyme NAD+ would lead to reagentless sensors. This is a subject of forthcoming investigations... 

Improving bioanodes performances and efficiencies will be the most important task in future studies of enzymatic anodic catalysis. Based on research carried out in the past few years, trends for improving performance rely on better electron transport methods and higher enzyme loading. Electron transport could be improved, for example, by developing novel mediators and redox polymers for MET or by controlling orientation of enzymes to improve DET. Enzyme loading techniques could be improved to increase active enzyme concentration per unit of electrode area or volume. 

Sensitive detection of other pollutants is achieved by various enzymatic biosensors. Integration of tyrosinase and redox polymers assures efficient catechol recycling between the enzyme and the polymer-bound redox sites leading to a detection limit of 10 nM for catechol.Nitrate biosensors based on NaR usually employ a cofactor or mediator, such as NADH and Azure A, by either adding to the measurement solution or immobilizing. Based on this sensing mechanism, nitrate biosensors can detect as low as 0.2 pM. °° The nitrate biosensor from the... 

More recently, a new series of water dispersed anionic polymers, the AQ 29D, 38D and 55D polymers were released by Eastman Kodak. Since that time, these polymers were used as electrode modifier (12, 13), as covering membrane (14) and as support for enzyme immobilization (15, 16). AQ polymers are high molecular weights (14,000 to 16,000 Da) sulfonated polyester type polymers (17, 18). Their possible structures have been recently presented (18). The AQ polymer serie shows many interesting characteristics useful for the fabrication of biosensors. They are water dispersed polymers and thus compatible with enzymatic activity. They have sulfonated pendant groups similar to Nafion and they can act as a membrane barrier for anionic interferring substances and they offer the possibility to immobilize redox mediators by ion exchange. 

Mediated enzyme electrodes were also realized on combined microscale and nanoscale supports [300]. Bioelectrocatalytic hydrogels have also been realized by co-assembling electron-conducting metallopolypeptides with bifunctional building blocks [301]. More recently, redox-modified polymers have been employed to build biofuel cells [25, 70, 302, 303]. In 2003, an enzymatic glucose/02 fuel cell which was implanted in a living plant was introduced [147]. 

A direct electron transfer from entrapped quinohemoprotein alcohol dehydrogenase (QH-ADH) to a Pt electrode, via chains of the polypyrrole, acting as immobilization matrix, was demonstrated [152]. QH-ADH is able to translocate in a fast inner-enzymatic reaction, the electrons primarily accepted by PQQ to heme units located close to the outer protein shell, from where they can be transferred on the conducting-polymer chains (Fig. 13). A similarity between the electron-transfer pathway in multicofactor proteins and that of mediator-modified electroenzymes is apparent, if one considers that a multicofactor enzyme can be regarded as a combination of a primary redox site and protein-integrated electron-transfer relays. 

Although less frequently considered as electrode coatings, polyphenazines, polyphenothiazines, and polyphenoxazines [48, 49] are very attractive ICPs, exploitable in some electroanalytical applications. The main interest for these materials lies in their capability to simultaneously act as both conducting polymers and redox mediators [50,51]. The applications as electrode coatings are particularly focused to the development of enzymatic sensors, both involving NAD(P)H and H2O2 detectirui [52, 53]. 

Suitable redox centers can also be inserted in the electrode coating with the aim to catalyze the oxidation or reduction of the product coming from the enzymatic reaction, such as H2O2 or nicotinamide adenine dinucleotide (NADH). This approach may allow the detection of the analyte at potential values where interfering species are not electroactive [107] and, in some cases, has also been proved to improve the electrode sensitivity [119]. Redox mediators can be adsorbed in the interlayer region of the clay [103,105,106,109,118] or constitute the brucite-like layers of conductive LDHs [104, 122]. Alternatively, bi-enzymatic electrode coatings have also been proposed [53, 108]. Organic polymers, namely poly(pyrrole-... 

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