pH-Controllable on-off bioelectrocatalysis of bienzyme layer-by-layer films assembled by concanavalin A and glucoenzymes with an electroactive mediator.

Mediated electrochemical biosensors consisting of two enzymes have attracted increasing interest because of their wider applicability. In this work, concanavalin A (Con A) and two glycoenzymes, horseradish peroxidase (HRP) and glucose oxidase (GOD), were assembled into {Con A/HRP/Con A/GOD}(n) layer-by-layer films on an electrode surface mainly by lectin-sugar biospecific interaction between Con A and glycoenzymes. The cyclic voltammetry (CV) response of Fe(CN)(6)(3-) at the bienzyme film electrodes was very sensitive to the environmental pH: at pH 4.0, the CV peak currents were quite large and the films were at the "on" state; at pH 8.0, however, the electrochemical response was significantly suppressed and the films were at the "off" state. By switching the film electrodes in solution between pH 4.0 and pH 8.0, the CV peak currents cycled between the on and off states, demonstrating the reversible pH-sensitive on-off switching. The pH-responsive property of the films toward the probe could be used to switch the on-off bioelectrocatalysis of glucose. That is, the electrochemical oxidation of glucose catalyzed by GOD and HRP in the films mediated by Fe(CN)(6)(3-) in solution could be controlled by changing the surrounding pH, allowing the reversible transition of bioelectrocatalysis between the on and off states. CV, electrochemical impedance spectroscopy, amperometry, and quartz crystal microbalance studies were used to characterize the {Con A/HRP/Con A/GOD}(n) films. The mechanism of pH-sensitive switchable behavior of the films was further explored by comparative experiments and should be attributed to the different electrostatic interactions between the films and the probes at different pH values. This pH-switchable bioelectrocatalysis based on the smart bienzyme interface may pave the way for designing novel controllable biosensors.