Photothermal Therapeutic Nanomaterials Composed of Plasmonic Aluminum Nanostructures for Effective Killing of Cells

Nanomaterial-based photothermal therapy is a noninvasive treatment approach that selectively destroys cancer cells by utilizing the ability of nanomaterials to convert photon energy into heat. Although plasmonic gold nanoparticles are promising, this study focuses on developing cost-effective alternatives. We developed plasmonic aluminum open-shell nanostructures (AlOSNs) as symmetry-breaking structures of nanoshells for this purpose. The intrinsic low chemical stability of AlOSNs in aqueous media (water and phosphate-buffered saline) was significantly improved by coating them with thin silica layers. We successfully adjusted the localized surface plasmon (LSP) resonance wavelength of aluminum within the biological transparency window region (700–950 nm) by optimizing the morphological parameters of AlOSNs. The AlOSNs exhibited a distinctive split resonance band around 800 nm, resulting from the pronounced optical interaction between the Al LSP and the strong interband transition (IT) of the Al metal, which occurs at the same wavelength. Consequently, a significantly high photothermal conversion efficiency (71%), attributed to the notable LSP-induced IT enhancement, was achieved by using an 808 nm laser as a light source. The AlOSNs of which surface was modified with folic acid through polydopamine were efficiently internalized into HeLa cells. It was confirmed by in vitro experiments that high cell viability was maintained even when AlOSNs was internalized. Upon irradiation with an 808 nm laser (1.7 W), HeLa cells incubated with AlOSNs at a concentration exceeding 5.0 μg/mL showed an effective cell death. These results indicate that plasmonic Al nanostructures hold significant potential as low-cost and excellent photothermal therapeutic materials for establishing noninvasive and efficient cancer treatment.