Visualization of OSA-HA Nanogels by TEM

OSA-HA nanogels were visualized using negative stain transmission electron microscopy (TEM). In short, 200 mesh formvar and carbon coated copper EM grids (Agar Scientific, Stansted, UK) were glow-discharged by 0.2 mbar air for 1 min using the glow discharger unit of an EMITECH K950X (Quorum Technologies, Lewes, UK). Three µL of OSA-HA nanogel solution (containing 150 µg/mL SAAP-148 and 500 µg/mL OSA-HA) was applied per glow-discharged grid for 1 min and the grids were blotted to remove excess of sample. Subsequently, the grids were stained on droplets of 2% (w/v) uranyl acetate in water for 1 min, after which excess staining solution was removed with blotting paper. Imaging of the air-dried grids was performed at 120 kV on a Tecnai 12 electron microscope (ThermoFisher, Waltham, MA, USA). A 4k × 4k Eagle camera (ThermoFisher) was used to record images at 11,000× magnification.