VISUALIZATION OF DENDRIMER MOLECULES BY TRANSMISSION ELECTRON-MICROSCOPY (TEM) - STAINING METHODS AND CRYO-TEM OF VITRIFIED SOLUTIONS

Individual dendrimer molecules of poly(amidoamine) (PAMAM) from genera tion 10 (G10) to G5 were imaged by conventional transmission electron microscopy (TEM) after staining with aqueous sodium phosphotungstate. The dendrimers were resolved as separate, beam-stable entities, and th eir sizes and distribution of sizes were statistically analyzed and co mpared with data from small-angle X-ray scattering in solution. Aqueou s G10 dendrimers were also characterized by examination in the frozen, hydrated state after quench-freezing in liquid ethane (cryo-TEM) and the data compared with the results of the staining experiments. To a f irst approximation, the dendrimers appeared circular in projection and the diameters conformed to a Gaussian distribution which broadened so mewhat with increasing generation number. Cryo-TEM, in general, confir med the staining experiments but suggested that, in the native state, there is more variability in the shapes of the dendrimers, with polyhe dral shapes occurring quite frequently.