Photochemical preparation of gold nanoparticle decorated cyclodextrin vesicles with tailored plasmonic properties

We report a photochemical strategy for the preparation of plasmonic vesicles by the in situ formation of gold nanoparticles at the surface of cyclodextrin host vesicle templates decorated with photoactive guest polymers. Upon irradiation with UV light, these carefully designed polymer shells undergo a Norrish type I reaction to generate reducing radicals for the in situ reduction of gold salts and simultaneously provide a stabilizing matrix allowing for a dense decoration with discrete gold seeds. In a highly controlled growth procedure the gold particle size can be adjusted between 3 and 28 nm resulting in an increasing interparticle plasmonic coupling as revealed by a pronounced redshift of the surface plasmon resonance (SPR) band and an enhanced absorption at wavelengths above 600 nm. This unique combination of cyclodextrin vesicles capable of specifically recognizing guest molecules with a plasmonic particle shell displaying multiple interparticle gaps acting as electromagnetic hotspots shows great potential for surface-enhanced Raman scattering (SERS) applications. Plasmonic vesicles are obtained by in situ photochemical reduction of gold salts at the vesicle surface using a stabilizing photoactive polymer shell that generates reducing ketyl radicals upon irradiation.