Visualizing Recombinant Adeno-Associated Viruses

Carbon-coated copper grids, 200 mesh (Science Services, Munich, Germany) were treated with oxygen plasma (Zepto, Diener electronic GmbH, Ebhausen, Germany). After this, 3 µL of precipitation-purified rAAV sample [25 (link)] was applied to the grid and incubated for 2 min. Excess liquid was drained off, the grid was dried at room temperature and washed with three drops of distilled water. Negative staining was performed using 3 µL 2% (v/v) uranyl acetate replacement stain (Science Services) for 30 s. Excess liquid was drained off and grids were dried before channeling the sample into the microscope. rAAVs were visualized with a CM100 (PW6021) instrument (Philips, Hamburg, Germany) with an acceleration voltage of 80 kV. Images were analyzed using the Soft Imaging Viewer (Olympus, Münster, Germany) and ImageJ [50 (link)].