Bimetallic Janus nanostructures via programmed shell growth.

We report the synthesis of compositionally asymmetric, core-Janus shell plasmonic nanostructures comprised of Au and Ag. Kinetic control was employed to achieve asymmetric shell growth on Au nanoparticles acting as cores. Subsequent differential surface functionalization of these nanostructures enabled programmed shell growth resulting in core-Janus shell nanostructures. UV/vis extinction spectra reveal that the localized surface plasmon resonance of the nanostructures depends on the composition and distribution of the components, providing additional handles to tune the optical properties of metal nanostructures. The core-Janus shell nanostructures demonstrated here are highly Raman-active making them attractive candidates for Raman-based biosensing and bioimaging applications.