3D SERS Imaging of Nanoporous Gold-Silver Microstructures:Exploring the Formation Mechanism Based on GalvanicReplacement ReactionPublished as part of The Journal of Physical Chemistry virtual special issue"Nanophotonics for ChemicalImaging and Spectroscopy br

The potential of three-dimensional surface-en-hanced Raman scattering (3D SERS) imaging has successfullybeen extended to investigate the transformation mechanism ofmetal contents in the galvanic replacement reaction of 3Dnanoporous silver microstructures (AgMSs). The galvanicreplacement reaction between AgMSs and Au3+occurs in asaturated sodium chloride solution at room temperature. Thegalvanized gold-silver microstructures (Au-AgMSs) with thedifferent mole ratios of Au3+and AgMSs were spontaneouslyfabricated due to the higher reduction potential of Au3+than thatof Ag+. 3D SERS images of AgMSs and Au-AgMSs wereconstructed using SERS signals ofpara-aminothiophenol (PATP)as a SERS probe. The Ag distribution in the microstructures wasexamined by microscopic and spectroscopic techniques to ensure the structural and morphological changes. 3D SERS profilessupport the existence of the atomic diffusion process on the Ag template surface, corresponding to previous studies that the activesite of the galvanic replacement reaction presents and forms a small hole for further replacement reaction. This process occurssimultaneously with the galvanic replacement reaction from the Ag surface to the interior of the structure. Therefore, thetransformation of Ag nanoparticles inside the microstructures can be observed in the 3D SERS profile, which cannot be acquireddirectly from other nondestructive techniques. Furthermore, the additional information about the stability of AgMSs against theatmospheric oxidation of silver metal was discussed for a critical selection of using it as 3D SERS substrates.