  Anisotropic Au nanoparticles show unique localized surface plasmon resonance
(LSPR) properties, which make it attractive in optical, sensing, and biomedical
applications. In this contribution, we report a general and facile strategy
towards aqueous synthesis of Au and M@Au (M = Pd, CuPt) hybrid nanostars by
reducing HAuCl4 with ethanolamine in the presence of cetyltrimethylammonium
bromide (CTAB). According to electron microscopic observation and spectral
monitoring, we found that the layered epitaxial growth mode (i.e., Frank-van
der Merwe mechanism) contributes to the enlargement of the core, while, the
random attachment of Au nanoclusters onto the cores accounts for the formation
of the branches. Both of them are indispensable for the formation of the
nanostars. The LSPR properties of the Au nanoparticles have been well
investigated with morphology control via precursor amount and growth
temperature. The Au nanostars showed improved surface-enhanced Raman
spectroscopy (SERS) performance for rhodamine 6G due to their sharp edges and
tips, which were therefore confirmed as good SERS substrate to detect trace
amount of molecules.
