Here, we demonstrate the formation of porous gold nanowires with diameters <60？nm by a two-step process involving the successive electrodeposition of silver then gold into the pores of a track-etched polycarbonate filtration membrane, followed by treatment with nitric acid. The resulting nanowires possess a unique, highly porous morphology, which yields a very high accessible surface area to volume ratio compared to solid nanowires of the same dimensions. Combined with the high aspect ratio of these particles (which allows for easy isolation from solution), this makes them eminently suitable for use in catalysis and sensing applications. The formation of such porous gold nanostructures was ascertained to result from the low diffusivity of the silver species within the narrow membrane pores. 1. Introduction Gold nanoparticles, discrete ensembles of gold atoms with one or more dimensions on the submicron scale, are materials that have attracted considerable interest in recent decades owing to their unique-size-dependant electronic and optical properties as well as their high unit surface areas [1, 2]; the combination of which makes them particularly suited to use in a variety of catalytic [3–9] and chemical sensor applications [10–15]. Typically, these applications utilize small solid nanoparticles ranging between 2–50？nm in diameter, as this size range is where such nanoparticles exhibit their useful properties [3–5, 16–21]. However, the use of such small nanoparticles presents a number of difficulties. For instance, gold nanoparticles with these dimensions possess rather high surface energies [22]. Therefore, in order to maintain a high unit surface area, the implementation of methods to stabilize them against aggregation is required [23, 24]. These methods must be carefully selected so that useful (in particular surface) properties are retained [25, 26]. Such small nanoparticles are also relatively difficult to separate from solution, making their reuse in applications costly. One recent development that promises to help overcome these issues has been the preparation of porous gold nanowires. Owing to their high aspect (length to diameter) ratios, such particles can be easily isolated from solution, while their porosity yields exposed surface features (known as ligaments) with dimensions suitable for use in applications, even when the particles as a whole are relatively large [27–30]. Such porosity also ensures that these particles have much higher surface areas relative to solid nanowires with equivalent dimensions. Furthermore, unlike solid
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