Preparation of controllable core-shell gold nanoparticles and its application in detection of silver ions

We report a novel shell technique to prepare controllable core-shell nanoparticles. In this technique, the shell is formed when the core reacts with metal ions and Na₂S₂O₃ and the size of the core and thickness of the shell can be controlled. Transmission electron microscopy and X-ray diffraction reveal that the shell consists of insoluble complex salts comprising Au₂S, AuAgS, and Ag₃AuS₂. The resulting core-shell nanoparticles obtained at different reaction stages demonstrate that the formation of Au₂S, AuAgS, and Ag ₃AuS₂ shell proceeds from the outside. The morphological evolution of the particles changes significantly with reaction time demonstrating that formation of the shell results from diffusion in the solid shell. The coreshell nanoparticles produced by this technique can be used as nanosensors to detect Ag⁺ in aqueous media with high selectivity and sensitivity. The excellent selectivity for Ag⁺ is demonstrated by comparing the response to other metal ions. In addition, our evaluation indicates that gold nanorods offer higher sensitivity than gold nanospheres. © 2010 American Chemical Society.