Tailored gold nanostructure arrays as catalysts for oxygen reduction in alkaline media and a single molecule SERS platform

Although plenty of functional nanomaterials are widely applied in science and technology, cost-efficient, controlled and reproducible fabrication of metallic nanostructures is a considerable challenge. Automated electrorefining by scanning electrochemical microscopy (SECM) provides an effective approach to circumvent some drawbacks of traditional homogeneous syntheses of nanoparticles, providing precise control over the amount, time and place of reactant delivery. The precursor is just a raw metal, which is the most economically viable source. This approach ensures reproducibility and the opportunity for fabrication of micropatterns, which can be rapidly analyzed by scanning probe techniques. Here, a cost-effective methodology for the preparation of naked (ligand-free) metallic nanostructures, from polycrystalline gold using a moving microelectrode, is presented. Automated micropatterning of bare gold on indium tin oxide (ITO) demonstrates the versatility of this method to tune the size and shape of the nanostructures. The morphology of the obtained materials and thus their catalytic and plasmonic properties can be tuned using the electrorefining parameters. Programmable fabrication of sample microarrays by microprinting followed by comparative SECM studies or spectroscopic analysis allows quick optimization and characterization for specific purposes. Electrocatalytic oxygen reduction in alkaline media and surface-enhanced Raman spectroscopy (SERS) of single porphycene molecules are presented as model examples.