The Effect of Electrodeposition Parameters and Morphology on the Performance of Au Nanostructures for the Detection of As (III)

Abstract

A series of Au nanospikes and dendrites were electrodeposited with either an inorganic (Pb 2+ ) or organic (cysteine) growth directing agent for different times to obtain varied morphology. These structures were compared with gold nanoparticles of three different shapes (Octahedral, Cubic and Rhombic Dodecahedral) for detection of As (III) by Square Wave Anodic Stripping Voltammetry (SWASV). The sensitivity and limit of detection (LOD) was dependent on the surface crystallographic orientations and the morphology, with superior sensitivity confirmed with a maximum amount of Au (111) facets on the surface for the nanoparticles. XRD studies suggested that the shape directing influence of Pb 2+ is lost on the gold nanospikes at higher deposition time, and that the size of the (111) terraces on the polycrystalline surfaces decreased, which led to a loss of performance. For gold dendrites, as the cysteine maintained shape directing behavior through hierarchical dendritic branching, deposition time did not affect the sensitivity. The study confirms that electrodeposition parameters or nanoparticle synthesis methods for Au surfaces in arsenic sensing needs to be carefully controlled, to either maximize the (111) facets, or minimize the steps on a polycrystalline Au surface, and that inorganic and organic shape directing agents will have differing effects. Arsenic (As) is a naturally occurring toxic substance associated with adverse health effects, including mutagenicity and carcinogenity.1 Contamination of groundwater by arsenic has been reported in more than 20 countries 2 with a recommended 10 ppb upper limit for drinking water set by the World Health Organization (WHO).3 Arsenite (As (III)) is considered the most toxic form in natural water, while Arsenate (As (V)) is 50 times less poisonous and generally the most stable in oxidising conditions. 4-7 Anthropogenic emissions of arsenic from industrial effluents, combustion of fossil fuels, or mining of As containing ores are a significant source, as are natural origins such as As bearing minerals. 8,9 A variety of conventional laboratory analytical techniques are available for arsenic detection including atomic absorption/fluorescence spectrometry, surface enhanced Raman scattering (SERS), high performance liquid/gas chromatography and inductively coupled plasma mass spectrometry (ICPMS).10 However, there remains a need for detection methods that are economically competitive, due to prevalent As in remote regions of the developing world, and such methods must be accurate and convenient for technicians to conduct on-site analysis. Electrochemical methods are useful to this end, 11 and a large range of materials have been developed for electrochemical detection of arsenic. Gold-based materials have been studied extensively for electrochemical detection of Arsenic (As), with the technique of Anodic Stripping Voltammetry (ASV) offering excellent sensitivity and limit of detection.12 Nanostructured Au electrodes have been shown to have a lower limit of detection (LOD) and h...

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