Tecnai g2 20 microscope

For room temperature electron tomography, 200 nm sections were made on a Leica UCT ultramicrotome (Leica Microsystems). After collecting the sections on a 50‐mesh Cu/Pd grid (Gilder Grids, Lincolnshire, UK), previously coated with a supporting film of formvar, 10 nm gold (Aurion) was put onto both sides of the section by incubating the grid in a drop of concentrated gold solution for 3 min. Tilt series were acquired at a Tecnai G2 20 microscope (FEI) equipped with an Eagle 4k HS CCD camera (FEI) and operated at 200 kV. Tilt series were collected with a tilting range from –60° to +60° at 1° increment. For data acquisition and processing the IMOD software from the Boulder Laboratory for 3D Electron Microscopy of Cells, University of Colorado Boulder was used.

For room temperature, electron tomography sections of a nominal thickness of 200 nm were made on a Leica UCT ultramicrotome (Leica Microsystems, Vienna, Austria). The sections were collected on a 50 mesh Cu/Pd grid (Gilder Grids, Lincolnshire, UK), previously coated with a supporting film of formvar, post‐stained with 2% aqueous uranyl acetate followed by Reynold's lead citrate. For tomogram alignment, 10 nm gold (Aurion) beads were put onto both sides of the section by incubating the grid in a drop of concentrated gold solution for 3 min. Tilt series were acquired at a Tecnai G2 20 microscope (FEI, Eindhoven, The Netherlands) equipped with an Eagle 4 k HS CCD camera (FEI, Eindhoven, the Netherlands) and operated at 200 kV. Dual‐axis tilt series were collected with a tilting range from −60° to +60° each at 1° increment. For data acquisition, processing and modelling the IMOD software from the Boulder Laboratory for 3D Electron Microscopy of Cells, University of Colorado Boulder, was used.
Videos S1 and S2 result from cells prepared for TEM taking samples in 20 nm distances. By fusing all images of different microscopy heights, a densitometric model can be obtained showing the native structure of intracellular inclusion bodies. Videos S1 and S2 thus show the imaging at different heights, whereas Figure 1E,F shows the results of the densiometric model.

The morphology of PbS CQDs film was measured by scanning electron microscope (SEM, FEI NovaNanoSEM450) and atomic force microscope (AFM, SPM-9700 Shimadzu Co.,Japan). Transmission electron microscopy (TEM) images were obtained using FEI Tecnai G2 20 microscope with a LaB₆ filament operated at 200 KV. The absorption spectra were measured by Shimadzu UV-3600 plus spectrophotometer. The crystal structure of PbS CQDs film was identified by X-ray diffraction (XRD, Philips, X pert pro MRD, Cu Kα radiation) with a step of 0.013°. The Fourier transform infrared (FTIR) spectra of PbS CQDs film were investigated using VERTEX 70 ATR-FTIR spectroscope (Bruker Co., Germany). The X-ray photoelectron spectroscopy (XPS) measurements were performed on AXIS-ULTRA DLD-600W Ultra spectrometer (Kratos Co. Japan).

A drop of the aqueous suspension of nanoparticles was added onto a piece of the carbon-coated copper grid, dried under ambient conditions, and then viewed under a transmission electron microscope (TEM; FEI Tecnai G220 microscope, FEI, Netherland) to examine the nanoparticle morphology. The morphology of the samples was characterized by scanning electron microscopy (SEM; Hitachi S-4800, Japan). The structure was characterized by X-ray diffraction (XRD; MAXima_X 17-XRD6000, China). The surface chemical composition and chemical states of the HCDs were determined by X-ray photoelectron spectroscopy (XPS; Rigaku D/MAX-2400, Thermo Scientific, USA). UV–visible spectrophotometry (RF-5301, Hitachi, Shimadzu, Japan) was used for the characteristic absorption peak. The zeta potentials were determined using a Horiba SZ-100 nanoparticle analyzer (Horiba, Kyoto, Japan) at 25 °C.

For electron tomography, cells were prepared as described in the previous section, except that 150–250 nm sections were cut on a Leica UCT ultramicrotome (Leica Microsystems). After collecting the sections on a 50 mesh Cu/Pd grid (Gilder Grids), previously coated with a supporting film of formvar, the section was covered on both sides with 10 nm gold (Aurion) by incubating the grid in a drop of concentrated gold solution for 3 min. Baking for 30 min was performed before collecting the tilt series to avoid shrinkage of the sample. Tilt series were acquired at a Tecnai G2 20 microscope (FEI) equipped with an Eagle 4k HS CCD camera (FEI) and operated at 200 kV. Dual axis tilt series were collected with a maximum tilting range from −60° to +64° at 1° increments. For data acquisition, processing and modelling, the IMOD software^{80 (link)} from the Boulder Laboratory for 3D Electron Microscopy of Cells was used.