Symmetry-Breaking Effects of Near-Infrared II Thermoplasmonics of Gold–Silica–Cuprous Selenide Hybrid Nanoshells

This study presents a numerical investigation of the plasmonic and photothermal properties of Au-silica-Cu2–xSe hybrid nanoshells (Cu2–xSe HNSs) consisting of a silica-Cu2–xSe core–shell nanoshell embedded with a spherical Au core at varied core offsets. The plasmon modes in the symmetry-broken Cu2–xSe HNSs are explained by plasmon hybridization theory in combination with charge density distribution. Results unveil that the hybridized plasmon modes in a symmetry-broken Cu2–xSe HNS arise from the interaction of the primitive plasmon modes of the same angular momentum on the Au core and the Cu2–xSe nanoshell. An increase in the core offset redshifts and weakens the near-infrared II (NIR-II) plasmon band corresponding to the low-energy bonding dipolar mode but redshifts and enhances the low-energy bonding quadrupolar mode. At the NIR-II plasmon resonance wavelengths, the temperature increase distribution is uniform on the Au core but inhomogeneous on the Cu2–xSe nanoshell. The variation of the temperature increase with the core offset suggests spectral tunability of NIR-II thermoplasmonic properties in the Cu2–xSe HNSs through varying the core offset. Our work provides a paradigm for rational design of NIR-II plasmonic materials with optimal photothermal performances for in vivo biomedical applications through symmetry breaking.