How are small and/or large test articles prepared for virus quantitation services?

For virus concentration, detection, and quantitation of large and small-volume test articles, the test article supernatant is concentrated by either ultracentrifugation and direct pelleting or by sucrose density gradient purification and ultracentrifugation.

The concentrated test article to be quantitated is prepared by mixing a known concentration of latex spheres and the unknown number of virus particles from the test article. This mixture is mounted onto grids, negatively stained, and examined in the transmission electron microscope. Both latex spheres and virus particles are enumerated, and the concentration of virus particles in the test article is determined by using ratio formulas.