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 Ag3AuS2 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 core−shell 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...