Formation of CdSe/CdS/ZnS–Au/SiO₂ Dual-Yolk/Shell Nanostructures through a Trojan-Type Inside-Out Etching Strategy

In this work we report the development of a rapid and selective etching strategy to synthesize a dual-yolk/shell nanostructure consisting of semiconductor–metal hybrid nanocrystals and hollow SiO₂ for the first time. By utilizing CdSe/CdS/ZnS quantum dot (CSSQD)/SiO₂ core/shell nanoparticles as the template and aurate hydroxyl complexes [Au(OH)₄^–] as the Trojan-type inside-out etching agent, rapid formation of CSSQD–Au hybrid nanocrystal dual-yolk and SiO₂ hollow shell occur during the reduction of Au(OH)₄^– on CSSQD cores accompanied by localized hydroxyl-liberation from Au(OH)₄^– at the interface between silica and CSSQD. Unlike surface-protected etching strategies, a selective as well as directional etching takes place from the silica internal surface and the thickness of the silica shell can be controlled by varying the etching time. Moreover, the size of attached Au nanoclusters can be tuned by subsequent light exposure. Consequently, the resulting platform offers a number of attractive features: (1) a new, directional, and rapid etching approach toward the formation of hollow silica nanostructures in solution; (2) semiconductor/metal hybrid nanocrystals as yolks within hollow silica nanospheres have been reported for the first time; and (3) the ability, through light exposure, to tune the size of the attached metal nanoclusters on the encapsulated CSSQD within the hollow silica nanospheres. Most importantly, the synthetic method has the capability of introducing additional guest species (e.g. metals) into a primary yolk (e.g. semiconductor) of hollow silica nanoparticles, potentially leading to many promising applications in fuel cells, photocatalysis, bioimaging, and cancer therapy.