Photothermal effects from Au–Cu2O core–shell nanocubes, octahedra, and nanobars with broad near-infrared absorption tunability

Abstract

Other than the display of purely optical phenomenon, the recently-discovered facet-dependent optical properties of metal–Cu₂O nanocrystals have become useful by illuminating Au–Cu₂O nanocubes and octahedra having a surface plasmon resonance (SPR) absorption band in the near-infrared (NIR) region from octahedral Au cores with 808 nm light for heat generation. After 5 min of light irradiation, a solution of Au–Cu₂O nanocubes can reach 65 °C with their Au SPR band matching the illuminating light wavelength. Photothermal efficiency has been found to be facet-dependent. In addition, short gold nanorods were employed to synthesize {100}-bound rectangular Au–Cu₂O nanobars with a tunable longitudinal Au SPR absorption band covering a broad NIR range from ∼1050 to 1400 nm. Because the Au SPR bands can become fixed with relatively thin Cu₂O shells of less than 15 nm, ultrasmall nanobars having a size of 61 nm directly red-shift the Au SPR band to 1047 nm. And 73 nm nanobars can give a Au SPR band at 1390 nm. Truncated nanobars exposing {100}, {110}, and {111} facets give a very blue-shifted Au SPR band. The nanobars also exhibit photothermal activity when illuminated by 1064 nm light. These small Au–Cu₂O nanocrystals represent the simplest nanostructure design to absorb light covering the entire NIR wavelengths.