pH-controllable bioelectrocatalysis of glucose by glucose oxidase loaded in weak polyelectrolyte layer-by-layer films with ferrocene derivative as mediator

Oppositely charged poly(allylamine hydrochloride) (PAH) and hyaluronic acid (HA) were assembled into {PAH/HA}n layer-by-layer (LBL) films on pyrolytic graphite (PG) electrodes. Glucose oxidase (GOD) in solution was then loaded into the films, designated as {PAH/HA}n–GOD. When the {PAH/HA}n–GOD film electrodes were placed in pH 5.0 buffers containing ferrocenedicarboxylic acid (Fc(COOH)2) and glucose, a well-defined and large cyclic voltammetric (CV) oxidation wave of glucose catalyzed by GOD immobilized in the films and mediated by Fc(COOH)2 in solution was observed. However, when the films were placed in pH 9.0 buffers containing the same amount of Fc(COOH)2 and glucose, the electrocatalytic response was quite small. The bioelectrocatalysis for the film system was at the “on” state at pH 5.0 and at the “off” state at pH 9.0. This pH-sensitive “on–off” behavior was reversible and could be repeated for several times. The possible mechanism of the pH-switchable bioelectrocatalysis was explored and discussed, and should be mainly attributed to the different electrostatic interaction between Fc(COOH)2 and the films at different pH. This work provides a novel model to realize pH-controllable bioelectrocatalysis based on the enzyme-loaded LBL assembly films, and may guide us to develop the tunable electrochemical biosensors based on electrocatalysis with immobilized enzymes.