Reversible "closing" of an electrode interface functionalized with a polymer brush by an electrochemical signal.

The poly(4-vinyl pyridine) (P4VP)-brush-modified indium tin oxide (ITO) electrode was used to switch reversibly the interfacial activity by the electrochemical signal. The application of an external potential (-0.85 V vs Ag|AgCl|KCl, 3M) that electrochemically reduced O(2) resulted in the concomitant consumption of hydrogen ions at the electrode interface, thus yielding a higher pH value and triggering the restructuring of the P4VP brush on the electrode surface. The initial swollen state of the protonated P4VP brush (pH 4.4) was permeable to the anionic Fe(CN)(6) redox species, but the electrochemically produced local pH of 9.1 resulted in the deprotonation of the polymer brush. The produced hydrophobic shrunken state of the polymer brush was impermeable to the anionic redox species, thus fully inhibiting its redox process at the electrode surface. The interface's return to the electrochemically active state was achieved by disconnecting the applied potential, followed by stirring the electrolyte solution or by slow diffusional exchange of the electrode-adjacent thin layer with the bulk solution. The developed approach allowed the electrochemically triggered inhibition ("closing") of the electrode interface. The application of this approach to different interfacial systems will allow the use of various switchable electrodes that are useful for biosensors and biofuel cells with externally controlled activity. Further use of this concept was suggested for electrochemically controlled chemical actuators (e.g. operating as electroswitchable drug releasers).