Biofriendly Route to Near-Infrared-Active Gold Nanotriangles and Nanoflowers through Nitric Oxide Photorelease for Photothermal Applications

The development of ecofriendly synthetic protocols for the fabrication of nonspherical gold (Au) nanoobjects with localized surface plasmon resonance (LSPR) falling in the near-infrared (NIR) region is one challenging topic in modern materials science. Among others, such metallic nanostructures have intriguing applications in nanomedicine because of their photothermal properties activated by light excitation in the so-called therapeutic window (λmax = 650-1300 nm). Here we report an unprecedented, simple, and "green" methodology to prepare water-dispersible Au nanotriangles and nanoflowers with NIR LSPR (λmax = 850-1250 nm). They are obtained in a single step at room temperature and in a few minutes by using one of the most biologically relevant molecules, nitric oxide (NO), generated by visible-light irradiation of a tailored β-cyclodextrin-branched polymer, without the need of preformed seeds, external reducing and sacrificial agents, conventional surfactants, and stabilizing ligands. Biocompatibility and effective photothermal applications of these metallic nanostructures are demonstrated by a photothermally activated enzymatic reaction and photothermal-induced sarcoma cancer cell mortality using 808 nm light. This approach may pave the way for completely unexplored, facile, and bio/ecofriendly synthetic protocols based on the photogeneration of NO through biocompatible polymeric scaffolds, for the preparation of Au nanostructures directed toward bioapplications.