*2.1. Materials*

EDTA, EDTA disodium salt, and EDTA tetrasodium salt were purchased from Samchun Chemicals (Seoul, Korea). Tetrachloroaurate trihydrate (HAuCl4·3H2O) was purchased from Strem Chemicals, Inc. (Newburyport, MA, USA). Methoxy poly(ethylene glycol)sulfhydryl (mPEG-SH, M w = 5000) was purchased from SunBio Corp. (Anyang, Korea). Water deionized by a Nano Pure System (Barnstead, Thermo Fisher Scientific, Waltham, MA, USA) was used. The chemicals used for the preparation of the solutions were purchased at the highest grade possible, and used without further purification.

### *2.2. Shape-Controlled Synthesis of Au Nanostructures*

To synthesize Au nanowires with a network structure, 15 mg of EDTA tetrasodium salt was injected into 7 mL of deionized water at room temperature, and the mixture solution was stirred for a few minutes to ensure complete dissolution of the salt. Further, 0.1 mL of 0.1 M HAuCl4 was added to the aqueous solution containing the EDTA tetrasodium salt at room temperature, and the resulting solution was vigorously stirred for 1 h. After the reaction, the mixture was washed with water by centrifugation at 14,000 rpm for 10 min. To synthesize the branched Au nanoparticles, the molar ratio of HAuCl4 to EDTA tetrasodium salt was changed to 1:6, and other conditions were kept constant. To synthesize the spherical Au nanoparticles, the molar ratio of HAuCl4 to EDTA tetrasodium salt was increased to 1:8.

To stabilize the Au nanowire networks, an mPEG-SH aqueous solution prepared by dissolving 40 mg of mPEG-SH in 2 mL of deionized water was injected into the mixture solution and further stirred for 30 min. The resulting solution was washed with water by centrifugation at 14,000 rpm for 15 min.

### *2.3. In Vitro Cytotoxicity against U87MG Cells*

U87MG human glioblastoma cells were grown as monolayer cultures in a 100-mm dish and subcultured 3 times a week at 37 ◦C in an atmosphere of 5% CO2 and 100% relative humidity. For the in vitro cytotoxicity assay, cells at a logarithmic growth phase were detached and plated (0.2 mL per well) in 96-well flat-bottomed microplates at a density of 10,000 cells per well, which were then left for 1–2 days at 37 ◦C to resume exponential growth. After washing the cells with phosphate buffered saline (PBS), 0.1 mL of the culture medium, with various concentrations of Au nanowire networks coated with mPEG-SH ligand, was added to the wells in quintuplicate. For the control wells, the same volume of culture medium was included in each experiment. Following 24 h of continuous exposure to the Au nanowire networks under 5% CO2 atmosphere at 37 ◦C, cell survival was assessed using the (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell proliferation assay.

### *2.4. In Vitro Photothermal Therapy*

The U87MG human glioblastoma cells were plated in a confocal dish and allowed to grow on the coverslip. Additionally, 150 μg Au/mL of the Au nanowire networks coated with mPEG-SH ligand were incubated with the cells for 24 h. The unbound Au nanowire networks were rinsed with the PBS buffer, and the cells were immersed in the culture medium.

Subsequently, a 980-nm continuous wave (CW) diode laser was used for irradiation and was focused to a 1-mm-diameter spot on the sample (power density: 38.2 W/cm2). The cells were irradiated for 10 min. The control cells without the Au nanowire networks with laser irradiation were also tested. Subsequently, the cells were stained with a few drops of 0.4% trypan blue to test viability. The dead cells were stained blue, while the live cells remained clear. After staining, the cells were rinsed with the PBS buffer and immersed in the culture medium for bright-field imaging.
