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pH-Sensitive “On−Off” Switching Behavior of Layer-by-Layer Films Assembled by Concanavalin A and Dextran toward Electroactive Probes and its Application in Bioelectrocatalysis

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journal contribution
posted on 10.12.2009, 00:00 authored by Huiqin Yao, Naifei Hu
Concanavalin A (Con A) and dextran (Dex) were assembled into {Con A/Dex}n layer-by-layer films on electrodes by the biospecific interaction between them. At {Con A/Dex}n film electrodes, the cyclic voltammetric (CV) response of different electroactive probes, such as Fe(CN)63−, Ru(NH3)63+, ferrocenecarboxylic acid (Fc(COOH)), and ferrocenedicarboxylic acid (Fc(COOH)2), was very sensitive to the solution pH. For example, in pH 4.0 buffers, the films showed good permeability toward Fe(CN)63−, leading to a well-defined CV peak pair of Fe(CN)63− with large peak currents at about 0.17 V vs SCE. In pH 9.0 buffers, however, the CV response of Fe(CN)63− was significantly depressed or even could hardly be observed. This pH-sensitive “on−off” switching property of the films toward the probe should be attributed to the different electrostatic interaction between Fe(CN)63− and the Con A constituent in the films at different pH and could be further used to control the electrocatalytic reduction of H2O2 by horseradish peroxidase (HRP) with Fe(CN)63− as the diffusional electron transfer mediator. Fc(COOH)2 showed the similar pH-dependent “on−off” behavior at {Con A/Dex}n film electrodes, and the corresponding pH-sensitive electrocatalytic oxidation of glucose by glucose oxidase (GOD) with Fc(COOH)2 as the mediator was also realized. This work provides a new interface system that has the pH-sensitive “on−off” CV property, and the better understanding of the interactions involved in this model system may guide us to develop the novel kind of controllable biosensors based on enzymatic electrocatalysis.