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The nanosheets were further analysed using a TEM. A drop of dispersion was casted on holy carbon grid (400 mesh) for the measurement. Low-resolution TEM imaging was conducted using FE-TEM manufactured by JEOL Ltd. with the acceleration voltage of 200 kV. The upper row of Supplementary Fig. 5 shows the typical images of 2D materials. We can observe monolayer, folded mono- or bi- layer, and few layers. In addition, thickness distributions of sheets were plotted through the investigation in TEM results as shown in the lower row of Supplementary Fig. 5. Overall, about 10% of the flakes were monolayer, and about 87 % of observed flakes were thinner than 5 layers. In fact, we can know that the dispersions prepared by present method contain very thin nanosheets.

TEM images of alum and PGA/Alum were obtained using a field-emission transmission electron microscope (FE-TEM; JEOL Ltd.). For visualization, alum and PGA/Alum (100 μg/ml) solutions were dropped and dried on a formvar- and carbon-coated copper grid (Ted Pella, Inc).

After rAAV infection, all cell media were removed by aspiration, and immediately add 250 μL of a warm (30–37 °C) 2% (vol/vol) glutaraldehyde solution by gentle pipetting. The cells were incubated at room temperature for 5 min and then placed on ice for 60 min. The cells were washed three times for ~ 1 min each time in 250 μL of cold (0–4 °C) 1 × sodium cacodylate, and then washes were performed gently, removing the liquid from the cells by aspiration. 250 μL of cold (0–4 °C) 20 mM glycine solution was added to cells for 5 min on ice and then removed by gentle aspiration and washed three times for 1 min each time in a cold buffer. After removing the buffer, 250 μL of 1 × DAB solution with 10 mM H₂O₂ was added for 5–45 min until a light brown stain was visible under a stereo light microscope, and then the DAB solution was removed and washed three times for 1 min each time in 1 × sodium cacodylate. Cells were pelleted via centrifugation at 1,000 rpm for 5 min and fixed with 2.5% glutaraldehyde (Sigma) for 1 day at 4 °C. The pellet was then incubated in 1% osmium tetroxide (OsO4, Sigma) for 1 h, dehydrated in a series of alcohol, and substituted with 100% propylene oxide. The cells were then embedded in the solution comprising propylene oxide and Epon812 for 24 h and solidified at 70 °C. Finally, the cells are sliced to a thickness of 70 nm and imaged by TEM (FE-TEM, JEOL).