One-step synthesis of highly dispersed gold nanocrystals on silica spheres.

Highly dispersed gold nanocrystals decorating silica spheres were prepared from HAuCl4 and NaOH via a deposition-precipitation (DP) process, in which the isoelectric point (IEP) of the substrate was adjusted during sphere synthesis by interaction of the surface with ammonia molecules. Through the systematic variation of pH (4-8), reaction temperature (65-96 degrees C), and time (10-30 min), a superior product with small (2-5 nm), homogeneously distributed gold crystals was obtained at pH 7 and a reaction temperature of 96 degrees C. These materials will offer enhanced performance as catalysts and contrast enhancers in biomedical imaging.