A new photothermal therapeutic agent: Core-free nanostructured Au _xAg_1-x dendrites

A new class of Au_xAg_1-x nanostructures with dendrite morphology and a hollow interior were synthesized by using a replacement reaction between Ag dendrites and an aqueous solution of HAuCl₄. The Ag nanostructured dendrites were generated by the reaction of AgNO₃ with ascorbic acid in a methanol/water system. The dendrites resemble a coral shape and are built up of many stems with an asymmetric arrangement. Each stem is approximately 400 nm in length and 65 nm in diameter. The bimetallic composition of Au_xAg_1-x can be tuned by the addition of different amounts of HAuCl₄ to the Ag dendritic solution. The hollowing process resulted in tubular structures with a wall thickness of 10.5 nm in Au_0.3Ag_0.7 dendrites. The UV/Vis spectra indicate that the strongest NIR absorption among the resulting hollow Au _xAg_1-x dendrites was in Au_0.3Ag_0.7. The MTT assay was conducted to evaluate the cytotoxicity of Ag dendrites, hollow Au_0.06Ag_0.94 and Au_0.3Ag_0.7 dendrites, and Au nanorods. It was found that hollow Au_0.06Ag _0.94 and Au_0.3Ag_0.7 dendrites exhibited good biocompatibility, while both Ag dendrites and Au nanorods showed dose-dependent toxicity. Because of absorption in the NIR region, hollow Au _0.3Ag_0.7 dendrites were used as photothermal absorbers for destroying A549 lung cancer cells. Their photothermal performance was compared to that of Au nanorod photothermal therapeutic agents. As a result, the particle concentration and laser power required for efficient cancer cell damage were significantly reduced for hollow Au_0.3Ag_0.7 dendrites relative to those used for Au nanorods. The hollow Au_0.3Ag _0.7 nanostructured dendrites show potential in photothermolysis for killing cancer cells.