ND and NG were purchased from SkySpring Nanomaterials (Houston, TX, USA). nGO were obtained from the Institute of Electronic Materials Technology through a modified Hummers method from NG as previously described.19 (link) The nanopowders were dispersed in ultrapure water to prepare a 1.0 mg/mL solution. Immediately prior to exposure to cells, hydrocolloids of nanoparticles were sonicated for 30 min and diluted to different concentrations with supplemented Dulbecco’s Modified Eagle’s culture Medium (DMEM, Thermo Fisher Scientific, Waltham, MA, USA).
Transmission electron microscopy (TEM) images of nanoparticles were acquired with a JEM-1220 microscope (JEOL, Tokyo, Japan) at 80 kV, with a Morada 11 megapixel camera (Olympus Soft Imaging Solutions, Münster, Germany) (Figure S1 ). Samples were prepared by placing droplets of hydrocolloids onto formvar-coated copper grids (Agar Scientific Ltd, Stansted, UK) and air dried before observations.
Zeta potential measurements were carried out with Nano-ZS90 Zetasizer (Malvern Instruments, Malvern, UK) at 25°C, using the Smoluchowski approximation. Each sample was measured after 120 s of stabilization at 25°C (20 replicates). Hydrodynamic diameter of nanoparticles in water was measured with dynamic light scattering (DLS) using a Nano-ZS90 Zetasizer (Malvern).
Nanoparticles were examined by vibrational spectroscopy. Raman scattering was studied at 2.33 eV (532 nm visible [VIS] laser) for the NG and nGO powders. The ND powder was analyzed at 4.66 eV (266 nm ultraviolet [UV] laser) due to the strong fluorescence of ND in the VIS spectrum. An argon laser was used as the source of the VIS laser, whereas a Crylas FQCW266-50 diode pumped continuous wave solid-state laser (Berlin, Germany) was used as the source of UV. The scattered light was dispersed by a Jasco NRS 5100 (Easton, PA, USA) spectrometer working in back-scattering mode. During the measurements, the laser beams were focused onto 10 μm spots. Nanoparticles were placed on a silicon substrate. For NG and nGO, spectral resolutions were fixed at 8.4 cm−1 and 3.5 mW laser power. In the case of ND, the spectral resolution was fixed at 20 cm−1 and 5 mW laser power.Figure S2 shows the registered Raman spectra of ND, and Figure S3 presents the comparison of the NG and nGO Raman spectra.
Transmission electron microscopy (TEM) images of nanoparticles were acquired with a JEM-1220 microscope (JEOL, Tokyo, Japan) at 80 kV, with a Morada 11 megapixel camera (Olympus Soft Imaging Solutions, Münster, Germany) (
Zeta potential measurements were carried out with Nano-ZS90 Zetasizer (Malvern Instruments, Malvern, UK) at 25°C, using the Smoluchowski approximation. Each sample was measured after 120 s of stabilization at 25°C (20 replicates). Hydrodynamic diameter of nanoparticles in water was measured with dynamic light scattering (DLS) using a Nano-ZS90 Zetasizer (Malvern).
Nanoparticles were examined by vibrational spectroscopy. Raman scattering was studied at 2.33 eV (532 nm visible [VIS] laser) for the NG and nGO powders. The ND powder was analyzed at 4.66 eV (266 nm ultraviolet [UV] laser) due to the strong fluorescence of ND in the VIS spectrum. An argon laser was used as the source of the VIS laser, whereas a Crylas FQCW266-50 diode pumped continuous wave solid-state laser (Berlin, Germany) was used as the source of UV. The scattered light was dispersed by a Jasco NRS 5100 (Easton, PA, USA) spectrometer working in back-scattering mode. During the measurements, the laser beams were focused onto 10 μm spots. Nanoparticles were placed on a silicon substrate. For NG and nGO, spectral resolutions were fixed at 8.4 cm−1 and 3.5 mW laser power. In the case of ND, the spectral resolution was fixed at 20 cm−1 and 5 mW laser power.
