Fine tuning the optical properties of Au–Ag nanocages by selectively etching Ag with oxygen and a water-soluble thiol

We present a facile method for fine tuning the optical properties of Au–Ag nanocages with oxygen (from air) and a water-soluble thiol. When nanocages were dispersed in an aqueous solution containing the thiol, the pure Ag inside the cages was selectively etched away. As a result, the wall thickness of the nanocages decreased and the localized surface plasmon resonance (LSPR) peak was red shifted. We also found that the extent of etching and LSPR peak position could be both controlled by varying the concentration of the thiol solution, allowing us to tailor and tune the optical properties of nanocages without involving galvanic replacement and dealloying reactions.