Dynamic Color-Switching of Plasmonic Nanoparticle Films

The fast and reversible switching of plasmonic color holds great promise for many applications, while its realization has been mainly limited to solution phases, achieving solid-state plasmonic color-switching has remained a significant challenge owing to the lack of strategies in dynamically controlling the nanoparticle separation and their plasmonic coupling. Herein, we report a novel strategy to fabricate plasmonic color-switchable silver nanoparticle (AgNP) films. Using poly(acrylic acid) (PAA) as the capping ligand and sodium borate as the salt, the borate hydrolyzes rapidly in response to moisture and produces OH^- ions, which subsequently deprotonate the PAA on AgNPs, change the surface charge, and enable reversible tuning of the plasmonic coupling among adjacent AgNPs to exhibit plasmonic color-switching. Such plasmonic films can be printed as high-resolution invisible patterns, which can be readily revealed with high contrast by exposure to trace amounts of water vapor.