Layer-by-layer self-assembly of glucose oxidase with a poly(allylamine)ferrocene redox mediator

We report the redox mediation of glucose oxidase (GOx) in a self-assembled structure of cationic poly(allylamine) modified by ferrocene (PAA-Fc) and anionic GOx deposited electrostatically layer-by-layer on negatively charged alkanethiol-modified Au surfaces. Successive PAA-Fc and GOx layers were deposited by alternate immersion of the thiol-modified Au in the respective polyelectrolyte and enzyme solutions. The uptake of thiol, redox polymer, and GOx on the surface was monitored by quartz crystal microbalance. Cyclic voltammetry shows nearly ideal surface waves of ferrocene in the polymer with charge independent of sweep rate; the redox surface concentration was obtained from integration of the ferrocene/ferricinium voltammetric peaks. The redox charge increases in step with the number of PAA-Be layers deposited. Enzyme catalysis for the oxidation of beta-D-glucose was achieved with a multilayer PAA-Fc/GOx assembly, with each GOx layer contributing equally to the catalytic response. Only a small fraction of the active assembled GOx molecules are ''electrically wired'' by the ferrocene polymer although all of the enzyme could be oxidized by soluble ferrocenesulfonate when added to solution.