pH-Controllable bioelectrocatalysis based on "on-off" switching redox property of electroactive probes for spin-assembled layer-by-layer films containing branched poly(ethyleneimine).

Weak polybase branched poly(ethyleneimine) (BPEI) and strong polyacid poly(styrenesulfonate) (PSS) were assembled into BPEI/{PSS/BPEI}(n) layer-by-layer (LBL) films on electrodes by electrostatic interaction between them with spin-coating approach. The cyclic voltammetric (CV) response of ferrocenedicarboxylic acid (Fc(COOH)(2)) at BPEI/{PSS/BPEI}(n) film electrodes was very sensitive to the pH of the testing solutions. At pH 4.0, the probe showed a well-defined CV peak pair with relatively large peak currents for the films, while, at pH 7.0, the CV response was significantly depressed. By switching the film electrodes in buffers between pH 4.0 and 7.0, the CV peak currents changed periodically between a relatively high value at the "on" state and a very low value at the "off" state, indicating that the pH-sensitive "on-off" switching function of the films toward the probe is reversible. A series of comparative experiments indicates that the electrostatic interaction between the films and the probe plays a predominant role in deciding the pH-sensitive behavior of the films. This pH-dependent property of the films could be used to control or modulate the bioelectrocatalysis of glucose by glucose oxidase (GOD) with Fc(COOH)(2) as the mediator by changing the surrounding pH. This "smart" bioelectrocatalytic film system may establish a foundation for fabricating novel pH-controllable electrochemical biosensors.