A Photometric Procedure for Weight Determination of Submicroscopic Particles Quantitative Electron Microscopy

A photometric procedure for rapid determination of weight of isolated particles down to a size of 200 A is described. Under normal conditions of electron microscopy, weights of down to 10−18 g can be determined with an inaccuracy of less than 10%. By lowering the accuracy or using more elaborate measures (such as very low accelerating voltage) one to two orders of magnitude for the lower weight limit can be gained. The method can now be applied to population studies of biologic particles, especially those of inhomogeneous and odd-shaped entities. Individual losses of matter through the action of enzymes and the uptake of specific stains can be measured quantitatively. The method extends the possibilities of individual mass-weight determination to the biologically important region of submicroscopic particles.