Ag-Au Bimetallic Nanocubes with Enhanced SERS Property and Chemical Stability
Surface-enhanced Raman scattering (SERS) relies on the localized surface plasmon resonance and enhancement of electromagnetic fields around metal nanostructures to drastically increase the Raman scattering cross sections of molecules in close proximity to the nanostructures. It has been documented that Ag nanocubes embrace SERS properties with enhancement factors up to 106 at visible excitation wavelengths for highly sensitive detection of chemical or biological species.
Unfortunately, elemental Ag is highly susceptible to oxidation under conditions that involve oxidants, halide ions, acids, water, UV-irradiation, and heating. Such chemical instability often results in changes to the morphology of Ag nanostructures, particularly at corners and edges with high surface free energies, and ultimately compromise their performance in SERS. One potential solution to improve the chemical stability of Ag nanostructures is to form alloy with a more stable metal such as Au. In this talk, I will report an approach to complementing the galvanic replacement reaction between Ag nanocubes and HAuCl4 with co-reduction by a reducing agent for the formation of Ag-Au hollow nanostructures with enrichment of Ag to greatly enhance SERS activity. Additionally, I will report our latest development in the replacement-free seeded growth of Au on Ag nanocubes with excellent SERS property and chemical stability.