Uranyl Formate Staining of DNA-VLP

Uranyl formate staining of DNA-VLP samples was adapted from an existing protocol^{97 (link)}. Briefly, DNA-VLP-30x was diluted to 5 nM, and 5 µl of the solution were immediately deposited onto glow-discharged electron microscopy grids. After 30 s, the solution was removed by blotting with filter paper and the grids were washed with 5 µl of freshly prepared 2% uranyl formate with 5 mM NaOH. After removal of the washing solution by blotting, 15 µl of the uranyl formate solution was added, incubated for 30 s and the removed by blotting. Finally, the grids were dried in vacuo and transmission electron microscopy (TEM, FEI Tecnai G2 Spirit Twin) was conducted at 120 keV.