Fine‐tuning the Homometallic Interface of Au‐on‐Au Nanorods and their Photothermal Therapy in the NIR‐II Window

The localized surface plasmon resonance (LSPR) of plasmonic nanomaterials is highly dependent on their structures. Going beyond simple shape and size, methods of further structural modification usually involve the growth of a wetting layer on seeds, or the growth of a non‐wetting island. In general, the structural tunability is still low and it hinders the exploration of plasmonic nanostructures. Here, we provide two new dimensions of synthetic controls in Au‐on‐Au homometallic nanohybrids: the number of the Au islands and the emerging shapes. By controlling the interfacial energy and growth kinetics, a series of Au‐on‐AuNR hybrid structures are successfully obtained, with the newly grown Au domains being sphere, polyhedron, and branched wire (nanocoral). The structural variety allowed the LSPR to be fine‐tuned in full spectrum range, making them excellent candidates for plasmonic applications. Importantly, the nanocorals exhibit black‐body absorption and outstanding photothermal conversion capability in NIR II window. In vitro and in vivo experiments verified them as excellent photothermal therapy and photoacoustic imaging agents.