Nanoelectrum across the Visible Spectrum: Tailored Ag–Au Alloy Nanoparticles with Glutathione-Enhanced Stability

Nanoelectrum (Ag-Au alloy nanoparticles, Ag-Au NPs) combines the unique nanoscale characteristics of silver and gold into a single bimetallic system exhibiting synergistic properties distinct from those of individual metals. Despite their significant potential and enhanced performance in applications such as catalysis and surface-enhanced Raman spectroscopy (SERS), the use of Ag-Au NPs remains limited due to challenges in achieving controlled and reproducible synthesis. Here, we present surfactant-assisted and surfactant-free approaches for the synthesis of both hollow and solid Ag-Au NPs from AgNP seeds across a wide range of Ag to Au ratios and AgNP sizes. We highlight the synergistic role of Cl^- ions and reducing agents in controlling the extent of galvanic replacement and minimizing the loss of Ag. In addition, we demonstrate for the first time the use of glutathione (GSH) as a postsynthetic capping agent to preserve structural integrity and ensure long-term colloidal stability of hollow Ag-Au NPs. These findings provide a much needed versatile and practical framework for fine-tuning the size, shape, and composition of Ag-Au NPs, facilitating the rational design of plasmonic bimetallic systems across the visible spectrum.