Physicochemical properties of GNPs in water and medium.

*- Claimed by the vendor.The concentration of Au within the GNP stock solutions was determined by Agilent Technologies 7500 ce ICP-MS, and it corresponded to the concentrations of Au reported by the vendor. The samples of GNPs (20 µg/ml) were prepared in DI 18 MEΩ water or complete medium, and sonicated for 20 s before the analysis by TEM or dynamic light scattering (DLS). The core size was analyzed on the preparations of GNPs added dropwise on the Cu-based grids and dried at room temperature, before the observation by JOEL JEM-2100 HR TEM (Tokyo, Japan) at 100 kV. The core size was similar in water and medium, so the average value from the measurements of GNPs in both solutions is shown as mean ± SD. Hydrodynamic size, polydispersion index (PDI), and z-potential in water and medium were analyzed by Zetasizer Nano ZS with non-invasive backscatter optics (NIBS). The samples were pre-warmed to 25°C for 120 s, and then analyzed for 15 min per run, for a total of 4 runs per sample, and the results are shown as mean ± SD (4).