Silver Nanocubes and Gold Nanocages: Fabrication and Optical and Photothermal Properties

The paper presents experimental data on fabrication, optical, and photothermal properties of silver nanocubes and gold-silver nanostructures based on silver cube templates. The silver cubes were obtained using polyol synthesis with a sulfide-mediated reduction of silver nitrate by ethylene glycol in the presence of poly(vinyl pyrrolidone). A galvanic replacement method was used to fabricate gold-silver nanoparticles of various structures, starting from silver-gold alloy particles and ending by target gold nanocages. The gold nanocages formation was controlled by shifts of the extinction and differential light scattering plasmon resonances, the transmission and scanning electron microscopy, the electronic-spectroscopy analysis (ESI), the dark-field microscope light scattering, and by visual inspection of colloid colors. The comparative experimental data on the laser heating kinetics are presented for three particle types: gold nanorods, silica/gold nanoshells, and gold nanocages. For suspensions with equal optical density at the laser heating wavelength (near plasmon resonances at 800 nm), all three particle types revealed close photothermal parameters. However, the specific photothermal efficiency per metal particle mass was maximal for gold nanocages followed by gold nanorods and silica/gold nanoshells. A coupled dipole spheres method was used to calculate the extinction and absorption spectra of randomly oriented particles by an analytical solution for random orientation averaging. The nanoparticles were modeled by arrays of interacting spheres with small intersection and polarizability calculated through the first Mie coefficient. The measured and calculated extinction spectra of silver cubes and gold nanocages are in good agreement.