Green synthesis of Au@Ag nanostructures through a seed-mediated method and their application in SERS

• A facile green synthesis is developed to fabricate well-dispersed Au@Ag nanostructures.
• The sizes of Au@Ag nanostructures can be tuned through adjusting the amount of Au seeds.
• The first formed Au-seeds acts as nucleation sites for the formation of Au@Ag nanostructures.
• The Au@Ag nanostructures have the remarkable SERS effect on the probe molecule rhodamine 6G.

A facile bottom-up “green” synthetic route is reported by using epigallocatechin gallate (EGCG) extract from tea leaves as a reducing and stabilizing agent in aqueous solution to produce silver nanostructures through a seed-mediated method at room temperature. The obtained gold core silver shell nanostructures (Au@Ag), whose sizes can be tuned through adjusting the amount of seeds, present polygonal morphologies. Meanwhile, the formation mechanism of Au@Ag nanoparticle has been investigated, in which Au-seeds act as nucleation sites for the formation of silver nanoparticles. The as-prepared Au@Ag nanostructure deposited on the glass plate can become the substrate of surface-enhanced Raman scattering (SERS), which has the obvious SERS effect when rhodamine 6 G (R6G) is used as the probe molecular. The above results indicate that the more irregular the shape of Au@Ag nanostructure becomes and the larger the size of nanoparticle gets, the stronger the SERS signal is.

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