Tecnai tem

PtNPs were prepared following a previously reported seed-mediated synthesis.^{39 (link)} Briefly, 7.76 mL of a 0.2% (w/v) solution of H₂PtCl₆ were added to 100 mL of gently boiling H₂O. After 1.0 min, 2.37 mL of a solution containing sodium citrate (1%, w/v) and citric acid (0.05%, w/v) were added and the solution was allowed to boil for an additional 30 s. Next, 1.18 mL of a solution containing NaBH₄ (0.08%, w/v), sodium citrate (1%, w/v), and citric acid (0.05%, w/v) were added, and boiling was continued for 10 min. After cooling to room temperature, 3–4 nm Pt seed NPs were obtained.
A 1.0 mL aliquot of the PtNP seed solution was added to 29.0 mL of H₂O at room temperature. With stirring, 0.023 mL of a 0.40 M H₂PtCl₆ solution and 0.50 mL of a solution containing 1% sodium citrate and 1.25% l-ascorbic acid was added. The solution was then heated to boiling at the rate of 10 °C min^–1. The total reaction time was 30 min. After cooling to room temperature, the solution was transferred to a 35 mm dialysis sack (12 000 Da MWCO, Sigma-Aldrich) and submerged in 4 L of DI H₂O for 24 h to remove excess salts. The PtNPs were characterized by transmission electron microscopy (TEM, FEI Tecnai TEM), and found to have an average diameter of 22 ± 4 nm. A representative TEM image and a histogram showing the NP size distribution are provided in the ESI (Fig. S1†).

BEAS-2B cells infected with HCoV-OC43 for 72 hours were fixed in 2.5% glutaraldehyde followed by osmium tetroxide. After fixation, the cells were processed through ascending grades of ethanol, propanol and EMbed 812 epoxy resin. Ultrathin sections were cut and stained with Reynold’s lead citrate and 5% uranyl acetate. The sections were imaged using an FEI Tecnai TEM (Hillsboro, Oregon). Mitochondrial diameter was measured in control and infected cells (n = 40 each) using Gatan DigitalMicrograph 3.4 software and analyzed using Welch’s two sample T-test.