Gold nanowire electrodes in array: Simulation study and experiments

Recent developments in nanofabrication have enabled fabrication of robust and reproducible nanoelectrodes with enhanced performance, when compared to microelectrodes. A hybrid electron beam/photolithography technique is shown that permits discrete gold nanowire electrode arrays to be routinely fabricated at reasonable cost. Fabricated devices include twelve gold nanowire working electrode arrays, an on-chip gold counter electrode and an on-chip platinum pseudo reference electrode. Using potential sweep techniques, when diffusionally independent, these nanowires exhibit measurable currents in the nanoAmpere regime and display steady-state voltammograms even at very high scan rates (5000 mV s^-1) indicative of fast analyte mass transport to the electrode. Nanowire electrode arrays offer the potential for enhancements in electroanalysis including increased signal to noise ratio and increased sensitivity while also allowing quantitative detection at much lower concentrations. However, to achieve this goal a full understanding of the diffusion profiles existing at nanowire arrays is required. To this end, we simulate the effects of altering inter-electrode separations on analyte diffusion for a range of scan rates at nanowire electrode arrays, and perform the corresponding experiments. We show that arrays with diffusionally independent concentration profiles demonstrate superior electrochemical performance compared to arrays with overlapping diffusion profiles when employing sweep voltammetric techniques. By contrast, we show that arrays with diffusionally overlapping profiles exhibit enhanced performance when employing step voltammetric techniques.