Electrical wiring of Shewanella oneidensis MR-1 with osmium polymers of different redox potentials

Abstract: The results of studies have shown that the several applications such as microbial electrochemical system (MES), bio-electrochemical systems (BESs) and production of beneficial chemicals are due to electrochemical connection among electrodes and microorganisms. The following two factors are important in choosing the microbe mediated electrochemical biosensors: I) Binding of bacterial cells on the electrode, II) Efficient electron transfer (EET) between the electrode and the cells by a mediator. In this study, gram-negative bacterium Shewanella oneidensis MR-1 was used in MES due to its unique characteristic features such as metal ion-reducing bacterium and direct ET capability. Osmium redox polymers (ORPs) were acted as efficient electron transfer (EET) mediators to direct the electrochemical flow of biomaterials to electrods. In the present study, the effect of the formal potential (E0') of three flexible osmium redox polymers was investigated: [Os(4,4'-dimethoxy-2,2'-bipyridine)2(PVI)Cl]+ ([Os-DMOPVI]); [Os(4,4'-dimethyl-2,2'-bipyridine)2(PVI)Cl]+ ([Os-DMPVI]); and [Os(4,4'-dichloro-2,2'- bipyridine)2(PVI)Cl]+ ([Os-DCPVI]). The electron donating or withdrawing ability of the functional group on the bipyridyl ligands coordinated to the osmium redox center can greatly affect the Os (II/III) redox potential. Our results demonstrated that out of the three polymers, Os-DMPVI with E0' of +121 mV vs Ag|AgCl|KCl(sat.) had the greatest ability to produce electrical energy in the presence of lactate as a substrate because of the methyl functional group. Os-DMPVI polymer modified graphite electrode connected with S. oneidensis MR-1 exhibited a current density of 13.62 μA cm2 with a significant decrease in the start-up time for electrocatalysis.