Supra 40vp system

Scanning electron microscopy was carried out using a Zeiss SUPRA 40VP system. Samples were prepared by spreading 2 μL of the nanoparticle suspension in water on a silicon substrate. The sample was dried under ambient conditions and then sputter-coated with a gold-platinum alloy (15 s, 20 mA). Micrographs were acquired using the InLens mode with an accelerating voltage of 10 kV. Particle sizes were measured on micrographs acquired at a magnification of 200 000× using the Olympus Analysis software package. To ensure size measurement accuracy, at least 250 measurements were made per sample. For transmission electron microscopy measurements, a 4 μL aliquot of sample was adsorbed onto a holey carbon-coated grid (Lacey, Tedpella), blotted with Whatman 1 filter paper and plunge-frozen into liquid ethane at −180 °C using a vitrobot (FEI). Frozen grids were transferred onto a Talos electron microscope (FEI) using a Gatan 626 cryo-holder. Electron micrographs were recorded at an accelerating voltage of 200 kV using a low-dose system (50 e⁻ Å⁻²) and keeping the sample at −175 °C. Defocus values were −3 μm. Micrographs were recorded on a 4 × 4 K Ceta CMOS camera.