Surface plasmon resonance as a probe of interactions between a thin‐film gold electrode and an aqueous supporting electrolyte containing 1‐ethyl‐3‐methyl‐imidazolium ethyl sulfate ionic liquid

Surface plasmon resonance (SPR) and electrochemical measurements are combined in this work to study the interactions of a gold film electrode with aqueous electrolytes of an ionic liquid (IL), 1‐ethyl‐3‐methyl‐imidazolium ethyl sulfate. The optical response of the bulk electrolyte strongly affects the SPR angles, and the critical angle data help to separate these bulk effects from those arising strictly from the electrode surface. The optical parameters of the Au‐electrolyte system are determined by fitting the SPR angle‐spectra to calculated results of a multilayer reflectivity model. Both in the absence and in the presence of externally applied voltages, the SPR signal of the experimental interface is dominated by the dielectric behavior of the bulk electrolyte. No significant chemisorptions are detected for the IL contents (0.036–0.087 mole fraction) of the electrolytes used. The results demonstrate how angle resolved SPR measurements can be employed to determine the suitability of specific ILs as solutes for aqueous background electrolytes in electrochemical SPR sensing experiments. Copyright © 2011 John Wiley & Sons, Ltd.