"On-off" switchable bioelectrocatalysis synergistically controlled by temperature and sodium sulfate concentration based on poly(N-isopropylacrylamide) films.

In this work, poly(N-isopropylacrylamide) (PNIPAm) films were synthesized on a Au electrode surface through the electrochemically induced free-radical polymerization method. The "coil-to-globule" phase transition of PNIPAm films was sensitive to both environmental temperature and sodium sulfate (Na(2)SO(4)) concentration in solution and was detected by cyclic voltammetry (CV) of ferrocenecarboxylic acid (Fc(COOH)) probe. For example, in solutions containing no Na(2)SO(4) at 25 degrees C, the probe demonstrated a well-defined CV peak pair with large peak currents, showing the "on" state; at 35 degrees C, the CV response was significantly suppressed, showing the "off" state. By switching the film electrodes in solution between 25 and 35 degrees C, the CV peak currents cycled between the on and off states, demonstrating the reversible thermosensitive switching function of the films. Similarly, the reversible Na(2)SO(4)-concentration-sensitive "on-off" property of PNIPAm films toward Fc(COOH) was also observed. In particular, the influence of temperature and Na(2)SO(4) concentration on the on-off behavior of the films was not independent or separate, but synergetic or cooperative. The dual-responsive property of the films could also be used to switch the on-off bioelectrocatalysis. That is, the electrochemical oxidation of glucose catalyzed by glucose oxidase (GOx) and mediated by Fc(COOH) in solution could be controlled or modulated by changing the surrounding temperature, Na(2)SO(4) concentration, or both. This dual- and synergetic-triggered bioelectrocatalysis based on the "smart" PNIPAm interface system may establish a foundation for fabricating novel multiple factor-controllable biosensors.