Field emission gun

High-resolution
transmission electron microscopy (HR-TEM) images of the FGQD samples
were captured using a JEM-2100F transmission electron microscope equipped
with a field emission gun (200 kV; JEOL). XPS profiles were recorded
for both the samples using a VG ESCALAB 220i-XL system (Thermo Fisher
Scientific, Waltham). XPS and high-resolution scans were performed
at pass energies of 100 and 20 eV, respectively, and at an X-ray beam
size of approximately 100 μm. FGQD samples for XPS measurement
were prepared on a silicon substrate by the spin-coating method with
the rotation speed adjusted to 2000 rpm. The samples were dried overnight
in a vacuum oven at 80 °C prior to the measurements. Room-temperature
PL spectra were recorded using a PL spectrophotometer (FluoroMax Plus
fitted with 150 W xenon arc lamp, HORIBA, Kyoto, Japan) in the wavelength
range of 300–800 nm. The PL emission spectra were recorded
at excitation wavelengths of 400, 450, and 500 nm. The above experimental
details are as per our previously published work.^{31 (link)}

Two different types of pristine (non-functional) SWCNT fibers (Lot No. HT0209-DA000 and HT0209-SA001, called SWCNT1 and SWCNT2, respectively) were obtained from Zeon Corporation (Tokyo, Japan). The surface areas were 1,100 and 650 m³/g, respectively. For transmission electron microscopy analyses, SWCNTs suspended in ethanol via vigorous sonication were spread directly over a copper grid with a plastic mesh and a carbon coat (Cat. No. 653; Nisshin EM). After drying, the fibers were analyzed. High-resolution transmission electron microscopy (HRTEM) images were obtained with a JEM-2100F high-resolution transmission electron microscope with a field emission gun (JEOL, Japan) operated at 80 keV under a pressure of <10⁻⁶ Pa at room temperature.
MWCNTs were also used as positive (MWCNT-50) and negative (MWCNT-tngl) controls. These fibers were previously fully characterized.^{13 )} Briefly, MWCNT-50 has a diameter of 50 nm and is highly inflammogenic and highly carcinogenic, whereas MWCNT-tngl has a diameter of 15 nm, is scarcely inflammogenic and induces no MM.^{14 )}