Osmium containing redox polymers

Pishko MV, Katakis I, Lindquist SE, Ye L, Gregg BA, Heller A. 1990. Direct electron exchange between graphite electrodes and an adsorbed complex of glucose oxidase and an osmium-containing redox polymer. Angew Chem 102 109-111. 

Figure 6.14 Components of an osmium containing redox hydrogel used to immobilize enzymes at electrode surfaces. Typically m = 1.2, n = 4, p = 1, and <7 = 10. Cross-links between the redox polymer chains are formed by reaction between the water-soluble diepoxide and amine groups on the polymer chains. (Adapted from [118] and [123].)...

Kang HL, Liu RG, Sun HF, Zhen JM, Li QM, Huang Y (2012) Osmium bipyridine-containing redox polymers based on cellulose and their reversible redox activity. J Phys ChemB 116 55-62... 

FIGURE 9.18. Components of an osmium containing redox hydrogel. The basic polymer is derived from Fig. 9.17, with n = 1, m = 4, and p = 1.2. The polymer is cross-linked using the water-soluble diepoxide according to the reaction shown (see Ref. 111). 

Acetylcholineesterase and choline oxidase A glassy C electrode surface was modified with osmium poly (vinyl-pyridine) redox polymer containing horseradish peroxidase (Os-gel-HRP) and then coated with a co-immobilized layer of AChE and ChO. A 22 pL pre-reactor, in which ChO and catalase were immobilized on beads in series, was used to remove choline. The variation in extracellular concentration of ACh released from rat hippocampal tissue culture by electrical stimulation was observed continuously with the online biosensor combined with a microcapillary sampling probe. Measurement of ACh and Ch was carried out by using a split disc C film dual electrode. 

A BASJ ion-exchange microbore column (45 cm x 1 mm i.d.) 0.05 Sodium phosphate buffer of pH 8.5 containing 0.1 mM EDTA [60 pL/min]. Electrochemical at horseradish peroxidase osmium redox polymer-modified vitreous C electrodes at 0 mV versus Ag/AgCl. Rat frontal cortex dialysate samples [188]... 

The examples described in this chapter clearly show the potential of modified electrodes based on redox-active osmium-containing polymers. The redox potentials of these materials can be manipulated by varying the nature of the polymer-bound redox couple, which allows us to tailor polymers to particular application, especially in the sensors area. Furthermore changes can also be made in the polymer composition both with respect to polymer loading and the nature of the polymer backbone. This will allow control of such parameters as substrate diffiision and charge transport through the layer. This flexibility allows the systematic investigation of electrochemical properties of electrodes modified with such materials. 

In the past decade, much work has been done on the exploration and development of redox polymers that can rapidly and efficiently shuttle electrons. Several research groups have wired the enzyme to the electrode with a long chain polymer having a dense array of electron relays. The polymer penetrates and binds the enzyme to the electrode. Gregg and Heller have done extensive work on osmium-containing polymers. They have made a large number of such polymers and evaluated their electrochemical characteristics [14]. Their most stable reproducible redox polymer was poly(4-vinyl pyridine) to which Os(bpy)3Cl2... 

A new type of (bio)chemical sensor, the redox-sensitive field-effect transistor is described It consists of a conventional ISFET with a noble metal added on top of the gate insulator The gate electrode is modified with a redox polymer containing osmium complexes The potentiostatic multi-puls method is introduced which allows the adjustment of the redox potential of the gate to a desired value in a stepwise way It is shown that the open circuit potential after switching off the potentiostat is a good measurement of the presence of the redox active species NADH... 

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 =... 

Figure 5. Dependence of current density on hydrogen peroxide concentration for cathodes based on different peroxidases, (open circles) NaI04 treated horseradish peroxidase (closed circles) native horseradish peroxidase (open squares) lactoperoxidase (closed squares) Aithromyces ramosus. Each electrode contains approximately 10/ g osmium redox polymer, polyethylene glycol diglycidyl ether crosslinker and 1 to 4/

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