The discovery could help fine-tune nanoparticle alloys for specific uses. Gold-silver alloys are useful catalysts that degrade environmental pollutants, facilitate the production of plastics and chemicals, and kill bacteria on surfaces, among other applications. In nanoparticle form, these alloys could be useful as optical sensors or to catalyze hydrogen evolution reactions. The team, from Rice University and the University of Duisburg-Essen in Germany, employed sophisticated microscopy to show how gold might retain enough silver to stabilize the nanoparticle. Their study appears in the journal The researchers used a hyperspectral dark-field imaging microscope to study gold-silver alloy nanoparticles containing an excess of silver in an acidic solution. The technique allowed them to trigger plasmons, ripples of energy that flow across the surface of particles when lit. These plasmons scatter light that changes with the alloy’s composition.