Development of Chemical Sensors Based on Redox-Dependent Receptors: N,N-Dimethyldiazapyrenium-Modified Electrodes

Electrodes modified with Nafion films containing 2,7-dimethyldiazapyrenium (DAP^2+) were prepared and characterized with voltammetry by themselves and in the presence of organic substrates. The large, planar, electron-poor aromatic surface in DAP^2+ facilitates (pi)-stacking interactions with other planar aromatic molecules, particularly those that are negatively charged or electron-rich. Previous studies showed that the reduction of DAP^2+ decreases the strength of these interactions, making the binding redox-dependent, and resulting in negative shifts in the E1/2 of DAP^2+/+. This study shows that the redox-dependent binding ability of DAP^2+ is retained in Nafion, but the selectivity is considerably different. Most significantly, the electron-rich, neutral aromatic compounds that produced small shifts in the E1/2 of DAP^2+/+ in solution cause much larger shifts, up to -110 mV, with the modified electrodes. With indole as a substrate, Nernstian behavior is observed (-60 mV shift per log[indole]) between 10 and 0.5 mM.