Single-step synthesis of various distinct hierarchical Ag structures

We introduce a convenient single-step approach for controlled synthesis of unique two- and three-dimensional hierarchical assemblies of silver nanoparticles by utilizing binary and ternary mixtures of capping agents. The binary mixtures comprise of trisodium citrate mixed with either cysteamine or mercaptopropionic acid while the ternary mixtures feature the addition of glucose. We observed the gradual evolution of silver nanoparticle assemblies from a closed-packed arrangement to a flower-like superstructure by simply adjusting the amount of trisodium citrate relative to a fixed amount of cysteamine. The addition of glucose to this binary mixture drastically changes the growth mechanism and instead resulted in nanodisc stacks; this is the first observation of such hierarchical silver nanodisc stacks. On the other hand, the addition of glucose to the binary mixture of mercaptopropionic acid and trisodium citrate produced belt-shaped ensembles with adjustable length. Interestingly, with increasing length, a secondary assembly of silver nanoparticles into petal-shaped structures occurred on the belt surface. While we show that all the structures we prepared can amplify surface enhanced Raman scattering signals, primarily due to their rough morphology, we believe our method can also be extended to other applications, since it provides a simple means to obtain both tuneable and drastically different predefined silver nanoensembles.