Histidine-directed formation of Ag octopods via pseudomorphic transformation of Ag2O

In this work, we demonstrated a facile approach for the formation of Ag octopods via pseudomorphic transformation of Ag2O by using histidine as a shape-directing agent. In this approach, Ag2O octopods were firstly formed via precipitation of AgNO3 in basic solutions, and their size increased with the increased concentration of histidine introduced into the solutions. After reduction of the Ag2O octopods by hydroxylamine, the resulting Ag particles well kept the shape and size of the Ag2O ones. Such pseudomorphic transformation allowed the formation of Ag octopods with tunable size (161–260 nm) and localized surface plasmon resonance (750–1380 nm), dependent on the concentration of histidine used in the reactions. Attributed to the well-defined size and morphology, the resulting Ag octopods showed well reproducible surface-enhanced Raman scattering (SERS) signals with a relative standard derivation lower than 5%, qualified as substrates in quantitative SERS detection.