Redox hydrogels

Hydrogels are crosslinked polymer networks with entrapped solvent. In the case of hydrogels containing polyectrolytes, in addition to solvent, ions and salt can be found in the gel as determined by the Dorman partition. This arises from the exclusion of ions of the same charge that sets a membrane potential at the gel/external electrolyte interface. 

Three-dimensional wired enzyme structures, based on crosslinking the redox polymer chains and binding these to glucose oxidase lysine amines, were subsequently designed and syntesized [36, 37]. An example of a polymerization reaction is 

Redox hydrogels have provided a significant contribution to development of BFCs, particularly with application to implantable devices with implications for in vivo 

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Figure 17.6 Redox hydrogel approach to immobilizing multiple layers of a redox enzyme on an electrode, (a) Structure of the polymer, (b) Voltammograms for electrocatalytic O2 reduction by a carbon fiber electrode modified with laccase in the redox hydrogel shown in (a) (long tether) or a version with no spacer atoms in the tether between the backbone and the Os center (short tether). Reprinted with permission fi om Soukharev et al., 2004. Copyright (2004) American Chemical Society.

Heller A. 2006. Electron-conducting redox hydrogels design, characteristics and synthesis. Curr Opin Chem Biol 10 664-672. 

Mano N, Soukharev V, Heller A. 2006. A laccase-wiring redox hydrogel for efficient catalysis of O2 electroreduction. J Phys Chem B 110 11180-11187. 

Electrode surfaces can be modified by redox polyelectrolytes via a sol-gel process, yielding random redox hydrogels or by layer-by-layer self-assembly of different redox and nonredox polyelectrolytes by alternate electrostatic adsorption from solutions containing the polyelectrolytes to produce highly organized redox-active ultrathin multilayers. 

IgG (rabbit) Sandwich immunoassay upon Os redox hydrogel/ avidin-modified SPCE Amperometric HRP-mediated electrocatalytic reduction of H2O2 +0.2 V lpgml-1 to lOngml-1 7 pgml-1 Zhang and Heller [85]... 

Glutamate Brain C CME Multienzyme redox-hydrogel under Nafion [50]... 

Neuron culture Pt DME Bienzyme redox-hydrogel coating [52]... 

Linke B, Kerner W, Kiwit M, Pishko M, Heller A. Amperometric biosensor for in vivo glucose sensing based on glucose oxidase immobilized in a redox hydrogel. Biosensors Bioelectronics 1994, 9, 151-158. 

Pishko MV, Michael AC, Heller A. Amperometric glucose microelectrodes prepared through immobilization of glucose-oxidase in redox hydrogels. Analytical Chemistry 1991, 63, 2268-2272. 

Poly[(vinylpyridine)Os(bipyridine)2Cl ] derivative based redox hydrogels (A)... 

Katakis and Heller [21] also applied the redox hydrogel to construct L-lactate and L-a-glycerophosphate sensors, where they observed electro-catalytic oxidation of both lactate and glycerol-3-phosphate at electrodes coated with three-dimensional redox polymer epoxy cross-linked networks which incorporated the respective oxidases. 

Recently, Kenausis et al. reported novel glucose and lactate sensors by constructing four polymer coated layers on vitreous carbon, based on wired thermostable soybean peroxidase and redox hydrogels (A) [54]. The first layer... 

Enzyme immobilization methods other than using the hydrogels (A) Since appUcations of the redox hydrogels (A) to glucose sensors was first reported by Pishko et al. in 1991, various other methods have been reported to immobilize redox polymers to construct biosensors as indicated (see Section 3.3.3.2). Other recent examples are as follows. 

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