3D SERS Imaging of Nanoporous Gold–Silver Microstructures: Exploring the Formation Mechanism Based on Galvanic Replacement Reaction

Abstract

The potential of three-dimensional surface-enhanced Raman scattering (3D SERS) imaging has successfully been extended to investigate the transformation mechanism of metal contents in the galvanic replacement reaction of 3D nanoporous silver microstructures (AgMSs). The galvanic replacement reaction between AgMSs and Au 3+ occurs in a saturated sodium chloride solution at room temperature. The galvanized gold−silver microstructures (Au-AgMSs) with the different mole ratios of Au 3+ and AgMSs were spontaneously fabricated due to the higher reduction potential of Au 3+ than that of Ag + . 3D SERS images of AgMSs and Au-AgMSs were constructed using SERS signals of para-aminothiophenol (PATP) as a SERS probe. The Ag distribution in the microstructures was examined by microscopic and spectroscopic techniques to ensure the structural and morphological changes. 3D SERS profiles support the existence of the atomic diffusion process on the Ag template surface, corresponding to previous studies that the active site of the galvanic replacement reaction presents and forms a small hole for further replacement reaction. This process occurs simultaneously with the galvanic replacement reaction from the Ag surface to the interior of the structure. Therefore, the transformation of Ag nanoparticles inside the microstructures can be observed in the 3D SERS profile, which cannot be acquired directly from other nondestructive techniques. Furthermore, the additional information about the stability of AgMSs against the atmospheric oxidation of silver metal was discussed for a critical selection of using it as 3D SERS substrates.

Nanophotonics for Chemical Imaging and Spectroscopy

“…Two studies that are included in this VSI are 3D SERS imaging of gold–silver nanostructures by Ozaki and co-workers (left) and high resolution TERS spectral imaging of a single molecule by Dong and co-workers (right). Reproduced with permission from refs and . Copyright 2022 American Chemical Society.…”

“…The above-echoed goal of characterizing increasingly complex interfaces comprises a recurrent theme in modern SERS-based spectroscopy and imaging studies. This VSI therefore includes a variety of SERS studies covering a broad range of fundamental and applied studies. − From work aimed at better understanding the unique optical properties of a single rod on a mirror to the ultrasensitive detection of plant biomarkers and herbicides, and through 3D SERS imaging of nanoporous gold–silver microstructures, the scope of SERS work in this issue is appropriately and exquisitely diverse. An interesting contribution that analyzed SERS hotspot dynamics in dry and aqueous environments is worth singling out .…”