Hybrid Au-SiO<inf>2</inf> core-satellite colloids as switchable SERS tags

Gold–silica self-assembled nanostructures are reported as multiplex surface enhanced Raman scattering (SERS) tags for bioimaging applications. These hybrid colloidal particles were obtained by heteroassembly of Au–SiO₂ Janus particles with smaller Au spheres and two Raman-active molecules that can be independently imaged by varying the wavelength of the excitation laser. The Janus structure of Au–SiO₂ not only directs the assembly but also provides physical separation of the Raman tags and colloidal stability thereby facilitating complete silica encapsulation. The bioimaging capabilities of this system are demonstrated through SERS mapping of individual cells.