Microelectrochemical Transistors Based on Electrostatic Binding of Electroactive Metal Complexes in Protonated Poly(4-Vinylpyridine): Devices That Respond to Two Chemical Stimuli

摘要

This article reports the fabrication and characterization of a microelectrochemical transistor derived from coating and connecting two closely spaced (< 1.7 micrometers) microelectrodes ( 80 micrometers thick) with poly (4-vinylpyridine ), (4-VPy)n. The transistor turns on only when two chemical criteria are met: the pH of the medium in contact with the (4-VPy)n must be sufficiently low to protonate the polymer to give (4-VPyH+)n and an anionic redox couple must be present to be electrostatically bound into the polymer, e.g. ferrie cyanide. By using conventional redox species as the mechanism for transporting charge from one microelectrode (source) to the other microelectrode (drain) the device shows a narrow region of gate voltage, VG, where the source-drain current, ID, is non-zero: ID (peak) occurs at VG E (ferrie cyanide) for a small difference (<50 mV) in potential between source and drain, VD. The temperature dependence of ID shows an Arrhenius activation energy of 50 kJ/mole, consistent with previous results for the (4-VPyH+ . 1/3 Fe(CN)63-)n polymer. The transistor can be turned alternately on and off in a reproducible manner by alternate exposure of the device to pH = 3 Fe(CN)63-/4- and pH = 3 cobalt cyanide, respectively, at VG= +0.2 V vs. SCE, consistent with dynamic exchange in and out of the (4-VPyH+)n by electroactive (Fe(CN)63-/4-) and non-electroactive (Co(CN)63-) anions. At pH's above the pka of the (4-VPy)n exposure of the device to Fe(CN) 63-/4- does not turn on the device.