Rapid virus subunit visualization by direct sedimentation of samples on electron microscope grids.

Airfuge direct ultracentrifugation of viral samples on electron microscope grids offers a rapid way for concentrating viral particles or subunits to facilitate their detection and study. Using the A-100 fixed angle rotor (30 degrees) with a K factor of 19 at maximum speed (95,000 rpm), samples up to 240 microliters can be prepared for electron microscopy observation in a few minutes: observation time is decreased and structural details are highlighted. Using latex spheres to calculate the increase in sensitivity compared to the inverted drop procedure, we obtained a 10- to 40-fold increase in sensitivity depending on the size of particles. Application of this technique to rubella virus permitted better visualization of viral membrane subunits on the particles. Rubella hemagglutinin immuno-stimulating complexes preparations were also better visualized and their morphology conserved after direct ultracentrifugation on the specimen grids. Similar observations are reported for respiratory syncytial virus associated subunits.