Gold nanocages for optical imaging and therapeutic applications

The galvanic replacement reaction between silver nanocubes and HAuCl4 in an aqueous solution transforms silver nanocubes of 10–200 nm in size into gold nanocages with tunable porosity. By controlling the molar ratio of silver to HAuCl4, the surface plasmon peaks of gold nanocages can be continuously tuned from the blue (400 nm) to the near infrared (1200 nm). These hollow and porous gold nanostructures have extraordinarily large cross-sections for both absorption and scattering, typically more than five orders of magnitude larger than those of conventional organic dyes. Exposure of gold nanocages to a camera flash resulted in the instant melting and conversion of gold nanocages into spherical particles due to photothermal heating. Gold nanocages can be easily bioconjugated with antibodies to target any specific cancer cells. This novel class of nanostructures is being developed as both a contrast agent for optical imaging in early-stage detection of cancer and a therapeutic agent for photothermal treatment of cancer, and as nanoscale capsules for targeted drug delivery.