Long tethers binding redox centers to polymer backbones enhance electron transport in enzyme "wiring" hydrogels

A redox hydrogel with an apparent electron diffusion coefficient (D-app) of (5.8 +/- 0.5) x 10(-6) cm(2) s(-1) is described. The order of magnitude increase in D-app relative to previously studied redox hydrogels results from the tethering of redox centers to the backbone of the cross-linked redox polymer backbone through 13 atom spacer arms. The long and flexible tethers allow the redox centers to sweep electrons from large-volume elements and to collect electrons of glucose oxidase efficiently. The spacer arms make the collection of electrons from glucose oxidase so efficient that glucose is electrooxidized already at -0.36 V versus Ag/AgCl, the reversible potential of the redox potential of the FAD/FADH(2) centers of the enzyme at pH 7.2. The limiting current density of 1.15 mA cm(-2) is reached at a potential as low as -0.1 V versus Ag/AgCl. The novel redox center of the polymer is a tris-dialkylated N,/\r-biimidazole Os2+/3+ complex. Its redox potential, -0.195 V versus Ag/AgCl, is 0.8 V reducing relative to that of Os(bpy)(2+/3+), its 2,2'-bipyridine analogue.