Diffusion profile simulations and enhanced iron sensing in generator-collector mode at interdigitated nanowire electrode arrays

Abstract

Gold interdigitated nanowire electrode arrays (INEAs) (∼100 nm wide, ∼50 nm high, ∼45 μm long and ∼500 nm spacing) on a Si/SiO2 chip substrate were fabricated and characterised. Arrays were employed in both non-generator-collector (non-GC) mode (one array electrically connected) and in generator-collector (GC) mode (both arrays electrically connected). In non-GC mode, the individual arrays were confirmed to behave as microelectrodes arising from linear diffusion to the total area of the array. By contrast, in GC-mode, arrays displayed steady-state electrochemical behaviour arising from enhanced diffusion to the nanowires and redox cycling (RC) between adjacent electrodes. Finite element simulations were investigated to explore the effect of altering connected and non-connected electrodes on the diffusional behaviour of the arrays with 500 nm separations. They correlated well with the experimental observations for the influence of the collector electrode potential on redox reactions taking place at the generator for a range of scan rates. The suitability of the gold INEAs towards iron sensing in water is also reported. A calibration curve is obtained for 0.5–40 μM (28–2234 μg L−1) Fe2+ with a limit of detection (LOD) of 0.01 μM (0.6 μg L−1) well below the permitted level in drinking water. Finally, iron determination in tap water using a standard addition technique is presented.