Effects of ferrocene methylation on ferrocene-modified linear poly(ethylenimine) bioanodes

Linear poly(ethylenimine) (LPEI) was modified by attachment of 3-(tetramethylferrocenyl)propyl groups to ca. 17% of its nitrogen atoms to form a new redox polymer, FcMe4-C3-LPEI, for use as an anodic mediator in glucose/O2 biofuel cells. Electrochemical properties of this polymer were compared to those of 3-(dimethylferrocenyl)propyl-modified LPEI (FcMe2-C3-LPEI). When FcMe4-C3-LPEI was complexed with glucose oxidase (GOx) and cross-linked with ethylene glycol diglycidyl ether (EGDGE) to form hydrogels on planar, glassy carbon electrodes, limiting catalytic bioanodic current densities of up to ∼1.4 mA/cm2 at 37 °C were produced. The use of tetramethylferrocene moieties in place of dimethylferrocene moieties lowered the E1/2 of the films by ca. 85 mV. FcMe4-C3-LPEI was shown to be the more effective polymer for use in biofuel cells and, when coupled with a stationary O2 cathode comprised of laccase and cross-linked poly[(vinylpyridine)Os(bipyridyl)2Cl2+/3+] (PVP-Os) as a mediator, produced power densities of up to 57 μW/cm2 at 37 °C. Power density increased to 126 μW/cm2 when a rotating biocathode was used. The power densities of biofuel cells made with either FcMe2-C3-LPEI or FcMe4-C3-LPEI were comparable. The FcMe2-C3-LPEI biofuel cells gave somewhat higher maximum currents, but the operating voltage and the stability of biofuel cells constructed with FcMe4-C3-LPEI was higher than that of cells using FcMe2-C3-LPEI. These polymers have immediate applications as amperometric glucose sensors as well as in biofuel cell materials and have the potential to be used in a wide range of small implantable electronic devices.