Effect of Mediator Spacing on Electrochemical and Enzymatic Response of Ferrocene Redox Polymers

The effect of mediator distance from the polymer backbone on the redox behavior, electron transport, electrochemical stability, and electrical communication with redox enzymes was studied with novel linear poly(ethylenimine) redox polymers. To measure these effects, we synthesized two new ferrocene redox polymers having a three-carbon (Fc-C-3-LPEI) and a six-carbon (Fc-C-6-LPEI) spacer to complement our previous synthesized polymer (Fc-C-1-LPEI) having a 1-carbon spacing. Increasing the spacer length to either three or six carbons resulted in a single peak redox behavior over the entire pH tested (3-11), which is in contrast with the multiwave redox behavior observed with a 1-carbon spacing under neutral or basic pH solutions. In addition increasing the spacer also resulted in a six-fold increase in the electrochemical stability of crosslinked redox polymer films. In contrast with previous reports of electron transport increasing with spacer length, we observed no correlation between mediator spacing and electron transport or electrical communication with the enzyme glucose oxidase. Surprisingly, the redox polymer (Fc-C-3-LPEI) with the lowest electron transport produced the highest enzymatic response (>1 mA/cm(2)), suggesting that other factors (e.g., polymer enzyme complexation) were important. These results demonstrate how small changes in the redox polymer structure can affect its properties.