Electroanalysis at discrete arrays of gold nanowire electrodes

Abstract

The development of reliable nanosensors offers a number of potential advantages in nanoscale analytical science. A hybrid electron beam-photolithography process was used to fabricate robust and reliable electrochemical nanowire array devices, with highly reproducible critical dimensions, 100±6nm. Nanowire electrode arrays were designed to permit diffusional independence at each nanowire element in an array thereby maximising limiting currents for optimised electrochemical nanosensing. The electrochemical behaviour of discrete nanowire electrode arrays was investigated using cyclic voltammetry in ferrocenemonocarboxylic acid. Single nanowire devices yielded highly reproducible steady-state sigmoidal waveforms, with typical currents of 179±16pA. Higher steady-state currents were achieved at nanowire arrays, up to ∼1.2nA for arrays consisting of six nanowire elements. At low and intermediate scan rates, sigmoidal waveforms were observed for nanowire arrays indicating very fast mass transport. However, voltammetric behaviour consistent with semi-infinite linear diffusion was observed at higher scan rates confirming the presence of overlapping diffusion profiles between neighbouring nanowires within an array. The existence of diffusion overlap between neighbouring nanowire elements was further demonstrated by deviation of measured steady-state currents from estimates, becoming more pronounced with increasing numbers on nanowire elements in the array. Finally capacitive charging of the electrodes was explored, and were found to exhibit very low capacitance typically ∼31±3nFcm−2 per device, three orders of magnitude less than that reported for conventional microelectrodes (∼20μFcm−2).