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Compared to bulk gold, highly reactive mesoporous gold film deposits are prepared on a boron-doped diamond electrode surface. An electroaggregation process causing 5 nm diameter gold nanoparticles to deposit cathodically from aqueous solution is implemented to control the amount of mesoporous gold at the electrode surface. The resulting electrode surface is characterized by electron microscopy and by cyclic voltammetry. The reactivity of the electroaggregated gold deposit towards arsenite is investigated in nitric acid media and in neutral phosphate buffer media. Three processes consistent with (i) cathodic deposition of arsenic metal (As(III) -> As(0)), (ii) anodic stripping (As(0) -> As(III)), and oxidation of arsenite (As(III) -> As(V)) are observed and shown to shift in potential with approximately 58 mV per pH unit (Nernstian at 20 degrees C). Improved anodic stripping voltammetry responses for solutions of arsenite(III) in 0.1 M HNO3 and in 0.1 M phosphate buffer solution are observed as the gold nanoparticle deposition time is increased. Typical detection limits of LOD(3 sigma) = 30 ppb in nitric acid and LOD(sigma) = 1 ppb in phosphate buffer (pH 7) are observed.