Shape-controllable gold nanostructures and their SERS enhancement

We report a new growth mechanism for the formation of gold (Au) nanoflowers (NFs) or Au nanoplates by simply tuning the solvent compositions. An aniline derivative N-(3-amidino)-aniline (NAAN) can reduce HAuCl₄ to form AuNFs in water, while individual Au microplates were prepared in N-methyl-pyrrolidone (NMP)/water mixed solvents. Growth mechanism showed that incomplete coverage of Au (111) facets by oxidized product poly (N-(3-amidino)-aniline) (PNAAN) resulted in AuNFs, and improved coverage on Au (111) facet by NMP was favorable for individual Au microplate formation. The layered AuNFs showed 11 times SERS enhancement compared with randomly packed Au microplate film. As low as 10⁻¹² M 4-mercaptobenzoic acid (4-MBA) can be detected using AuNF as a SERS substrate. (paper)