Separation of Silver Nanocrystals for Surface-enhanced Raman Scattering Using Density Gradient Centrifugation

One-dimensional silver nanocrystals (AgNCs) have been prepared by a polyol process using sodium hydroxide and nitric acid at a constant silver source concentration. Results indicate that the acidity-basicity plays an important role in silver-nanocrystal formation. Different morphologies of AgNCs were synthesized by changing the NaOH or HNO3 amount. We demonstrate that nearly monodisperse silver nanocrystals can be separated from polydisperse samples using density gradient centrifugation separation (DGCS). We also demonstrate that the separated AgNCs can be used as substrates for surface-enhanced Raman scattering (SERS) spectroscopy. The separation approach provides a method of improving the nanocrystal quality produced by large-scale synthetic methods.