Characterisation of Nanoporous Gold for Use in a Dissolved Oxygen Sensing Application

A nanoporous gold (NPG) microdisc array in a three-electrode electrochemical cell arrangement has been fabricated and characterised for a dissolved oxygen sensing application. The device will be used for monitoring of drinking water quality in rural communities in India, where there is a need for a miniaturised, low-cost dissolved oxygen sensor. The NPG microdisc array exhibits improved electrochemical responses compared to a planar gold microdisc array, owing to its extended surface area. In 1 mM ferrocene carboxylic acid, the experimental limiting currents obtained are twice as large as the theoretical limiting current for a planar gold microarray. A 252-nm-thick NPG layer resulted in a limiting current of 627 nA (compared to the estimated current of 295 nA). The voltammetric behaviour in water samples from a pilot site in India was investigated for increasing oxygen content, and a comparison was made with a macrodisc gold electrode and an unmodified microdisc array. The NPG microdisc array demonstrated improved characteristics over both devices and exhibited a higher correlation (average value 0.925) compared with the unmodified array (0.819) and macrodisc (0.870). An improvement in signal-to-noise ratio was also observed to be 12.349 versus 5.259 (microelecrode array) and 5.604 (macroelectrode). The response time for the NPG microdisc array versus a commercial dissolved oxygen sensor showed a faster response time of 20 versus 40 s.