Mediated electron transfer from microbial systems to electrodes represents a promising alternative to Clark electrodes. Electron mediators perform a special function in whole cell biosensors; their role is to replace the electron transfer performed by oxygen, thus preventing the process from the problem of having a low oxygen concentration [1]. Since the first applications of osmium redox polymers for enzyme based reagentless mediated biosensing were described, polymeric mediators still attract attention due to the efficient electron shuttling properties combined with the polymeric structure promoting a stable adsorption as well as a possibility for multiple layers of both immobilised enzymes [2] and microbial cells [3] on the electrode surface.
In the present study applications of flexible Os^2+/3+ functionalised polymers such as poly(1-vinylimidazole)₁₂-[Os(4,4'-dimethyl-2,2'-dipyridyl)₂Cl₂]^2+/3+ and poly(vinyl- pyridine)[Os(N,N'-dimethyl-2,2'-biimidazole)₃]^2+/3+ for efficient electrical wiring of bacterial cells is described. The methylated biimidazole complex was recently reported as a fast redox mediator due to its long tethering to the polymer backbone through a 13-atom-long flexible spacer [4] and also shown to more efficient than other Os-polymers having redox potential values 250-300 mV more positive. Gluconobacter oxydans and Pseudomonas putida DSM 50026 were used as the biological components serving both as model bacteria but also for possible future applications in biosensing and biofuel cells.

[1] P. Skladal, N. O. Morozova, A. N. Reshetilov, Biosens. Bioelectron., 17 (2002) 867.
[2] A. Heller, J. Phys. Chem., 96 (1992) 3579.
[3] I. Vostiar, E. E. Ferapontova, L. Gorton, Electrochem. Commun., 6 (2004) 621.
[4] F. Mao, N. Mano and A. Heller, J. Am. Chem. Soc., 125 (2003) 4951.