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Highlights: [•] Well-defined urchin-like Au arrays were facilely prepared by one-step electrodeposition. [•] Iron(III) ions serve as catalysts and growth directing agents. [•] This approach is simple, controllable and convenient, without any template, seed or surfactant. [•] The Au nanocrystals display high electrocatalytic activity toward the oxidation of ethylene glycol and glycerol. [ABSTRACT FROM AUTHOR]

We have developed a simple, sensitive and selective colorimetric method for the detection of cadmium(II) (Cd) using gold nanoparticles modified with 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole. Organic solvents or additives are not required. It is found that Cd induces the aggregation of the modified Au-NPs via chelation, leading to a color change from red to blue. This change can be seen with bare eyes, and monitored by UV-vis spectroscopy, transmission electron microscopy and dynamic light scattering. The detection limit is 30 nM (at a signal-to-noise ratio of 3). The new approach was successfully applied to the detection of Cd in spiked samples of tap water and lake water, and the results agree well with those obtained by flame atomic absorption spectroscopy. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]