Artificial mediators offer the possibility for an enhanced electron transfer between microbial cells and electrodes. The important role of these electron shuttles in whole cell biosensors and microbial fuel cells is to replace the natural electron acceptor (oxygen in case of aerobic bacteria, Fe(III) oxides/complexes in case of anaerobic organisms), thus preventing the problem of limiting concentrations. The polymeric mediators proved to exhibit efficient electron shuttling properties for multiple layers of microbial cells. They promote a stable binding on the electrode surface; therefore the problem of releasing possible human-toxic compounds in the environment is reduced. In the present study the application of two different flexible osmium redox polymers; poly(1-vinylimidazole)₁₂-[Os-(4,4′-dimethyl-2,2′-di'pyridyl)₂Cl₂]^2+/+ (osmium redox polymer I) and poly(vinylpyridine)-[Os-(N,N′-methylated-2,2′-biimidazole)₃]^2+/3+ (osmium redox polymer II) were investigated for efficient electrical wiring of gram-positive bacteria Bacillus subtilis. Their efficiency in wiring gram-negative bacteria was previously investigated [1,2]. The two Os-polymers differ in redox potential and the length of the side chains, where the Os^2+/3+-functionalities are located. The analytical characteristics of the microbial sensors were evaluated for determination of succinate, fumarate and glucose as substrates in both batch analysis and flow analysis mode using both gold and graphite electrodes. The influence of oxygen presence in the buffer on the current response was evaluated. The efficiency of the electron transfer with the osmium redox polymer was compared with that of a soluble mediator (ferricyanide).

[1] I. Vostiar, E. E. Ferapontova, L. Gorton, Electrochem. Commun. 6 (2004) 621.

[2] S. Timur, B. Haghighi, J. Tkac, N. Pazarlioglu, A. Telefoncu, L. Gorton, Bioelectrochemistry 71 (2007) in press.