Electron microscopical particle counting in virology. III. Parameters governing the efficiency of sedimentation techniques and its improvement with the application of poly-L-lysine.

In the preceding study the degree of adsorption of virus to electron microscope grids has been shown to be an important parameter governing the efficiency of sedimentation techniques used for particle counting. In the present study the application of poly-L-lysine not only improves the binding ability but makes it more reproducible. In addition the distribution of adsorbed particles between grid bars and holes is characterized and its importance as an additional parameter for such techniques discussed. For accurate particle titre estimation and for assessing the efficiencies of sedimentation techniques in virus diagnostics the product of these parameters represents a correction factor which must be taken into consideration. Furthermore it could be demonstrated, using the technique here described over the surface of a poly-L-lysine treated grid after drying. This phenomenon makes possible the estimation of a titre through particle counting on gravimetrically determined volumes.