Oxidation-Resistant Ag Nanostructures for Ultrastable Plasmonic Applications

Although Ag is considered a noble metal, its surface oxidizes relatively quickly on exposure to ambient air. On the nanos- cale, this degradation is especially deleterious to applications pertaining to its plasmonic behavior, such as surface plasmon resonance (SPR) sensing. In this Communication we show that oxidation of Ag nanoparticles under ambient conditions can be significantly suppressed by contacting Ag with immis- cible Co nanoparticles. As a consequence, while the plasmonic characteristic of pure Ag degrades by 25% within 500 h, Ag-Co nanoparticles take almost ten times longer to show a similar magnitude of decay in air, thus showing ultrastable plasmonics. We attribute this oxidation-resistance to a cathodic protection arising from galvanic coupling.