pH-switchable bioelectrocatalysis of hydrogen peroxide on layer-by-layer films assembled by concanavalin A and horseradish peroxidase with electroactive mediator in solution.

The lectin protein concanavalin A (Con A) and the glycoenzyme horseradish peroxidase (HRP) were assembled into {Con A/HRP}(n) layer-by-layer films on electrodes mainly by biospecific affinity between them. The cyclic voltammetric (CV) response of ferricyanide (Fe(CN)(6)(3-)) at {Con A/HRP}(n) film electrodes was very sensitive to the environmental pH. The peak currents of Fe(CN)(6)(3-) were quite large at pH 4.0 but greatly suppressed at pH 9.0, demonstrating reversible pH-sensitive "on-off" behavior. This property could be used to realize pH-controlled electrochemical reduction of H(2)O(2) catalyzed by HRP immobilized in {Con A/HRP}(n) films and mediated by Fe(CN)(6)(3-) in solution. The modulation of the solution pH was also realized by in situ biochemical reactions with various enzymes in solution and was used to tune the pH-switchable bioelectrocatalysis. The possible mechanism of the pH-responsive on-off behavior of the films toward the probe was explored, and the electrostatic interaction between the films and the probe is believed to play a key role in deciding the pH-sensitive behavior of the films. This "smart" interface may be used to establish a foundation for fabricating novel pH-controllable electrochemical biosensors based on bioelectrocatalysis with immobilized enzymes.