Synthesis of gold and palladium nanoshells by in situ generation of seeds on silica nanoparticle cores

Abstract

This report describes the synthesis of silica–metal core–shell nanostructures by in situ generation of metal seeds on polyethyleneimine silane functionalized silica core surfaces eliminating the need for pre-synthesized metal seeds and a subsequent aging step, currently essential for synthesis of these materials. Specifically, gold nanoshells are generated on silica cores of two different sizes (∼150 and ∼40 nm diameter), following this in situ seed generation method. In addition, an aqueous suspension of gold nanoshells with ∼150 nm silica core and ∼18 nm shell thickness shows characteristic photo-thermal properties with ∼16 °C temperature change occurring from room temperature (25 °C) within ∼10 minutes when exposed to an 808 nm wavelength laser. This in situ seed-mediated synthesis is further extended to palladium nanoshells (on a ∼200 nm diameter silica core), and this paper reports for the first time the synthesis of palladium nanoshells from in situ generated palladium seeds on a silica core, unlike earlier reports of palladium nanoshell synthesis using solely gold nanoparticles as seeds to grow the final palladium shell. Different palladium shell thicknesses are generated by varying the concentration of seed-attached silica cores during the final synthesis step. For both gold and palladium nanoshell synthesis, ultraviolet-visible spectroscopy and transmission electron microscopy are used to follow the different steps of this synthesis process. The results demonstrate that this in situ seed generation method is effective for gold nanoshell synthesis with varying core sizes as well as being able to produce nanoshells with different metal overlays.