pH-switchable bioelectrocatalysis based on layer-by-layer films assembled with glucose oxidase and branched poly(ethyleneimine)

Branched poly(ethyleneimine) (BPEI) and glucose oxidase (GOD) were assembled into {BPEI/GOD}_n layer-by-layer films on the surface of electrodes mainly by electrostatic interaction between them. The cyclic voltammetric (CV) response of ferrocenedicarboxylic acid (Fc(COOH)₂) at {BPEI/GOD}_n film electrodes was very sensitive to the environmental pH. The CV peak currents of Fc(COOH)₂ were quite large at pH 4.0 but greatly suppressed at pH 7.0, demonstrating reversible pH-sensitive on-off behavior. The factors influencing the pH-dependent switching behavior of the system were investigated. A series of comparative experiments supports the conclusion that the electrostatic interaction between the films and the probe plays a key role in deciding the pH-sensitive on-off behavior of the system. This smart interface could be used to realize pH-switchable electrocatalytic oxidation of glucose by GOD in the films and mediated by Fc(COOH)₂ in solution, which may establish a foundation for fabricating novel pH-controllable electrochemical biosensors based on bioelectrocatalysis with immobilized enzymes.