Dual-Plasmonic Yolk–Shell Au Nanoplate@Cu_2–<i>x</i>Se Hollow Spheres for Enhanced Near-Infrared II Photothermal Conversion

We report the design and synthesis of a dual-plasmonic yolk-shell nanostructure containing Au nanoplate@Cu_2-<i>x</i>Se hollow spheres with tunable selenium (Se) content, engineered to enhance NIR-II photothermal conversion performance. The fabrication process begins with the high-yield synthesis of Au nanoplates, which serve as both a structural template and a plasmonic core. A conformal Cu₂O layer is then grown on the Au nanoplate surface, followed by controlled selenization to convert Cu₂O into Cu_2-<i>x</i>Se, concurrently forming a yolk-shell architecture with a hollow interlayer. The Se content in Cu_2-<i>x</i>Se is systematically adjusted by varying the selenization conditions, enabling precise control over the shell composition, morphology, and optical absorption in the NIR-II region. The resultant products exhibit synergistic plasmonic responses from both the Au core and Cu_2-<i>x</i>Se shell, further validated by finite-difference time-domain (FDTD) simulations that confirm enhanced electromagnetic field confinement and broadened NIR absorption due to the dual-plasmonic coupling and hollow structural design. Spectroscopic and thermal characterization shows that the optimized products with tailored Se content achieve a high photothermal conversion efficiency of 45.32% under 1064 nm laser irradiation, attributed to their unique dual-plasmonic coupling, tunable composition, and hollow structure that enhances heat retention. This work demonstrates a facile strategy to engineer multicomponent plasmonic nanocomposites with tunable compositions, offering a promising platform for advanced NIR-responsive photothermal therapies.