Visualization and characterization of poly(amidoamine) dendrimers by atomic force microscopy

Poly(amidoamine), or PAMAM, dendrimers in the G5-G10 range were imaged by tapping mode atomic force microscopy (AFM). Individual dendrimer molecules could be clearly observed in the AFM images, which showed that these dendritic particles appear to be monodispersed, dome-shaped, and randomly distributed on the mica surface. Molecular diameter and height can also be measured from each particle's profile section from the AFM line scans. The diameter and height data were used to calculate the molecular Volume of each single molecule. Absolute molecular weight and polydispersity were then estimated for each dendrimer generation. The calculated molecular weights for G5-G8 were in very good agreement with theoretical values. In addition, lower generation dendrimers, such as G4, were also studied by AFM. Although individual molecules of G4 dendrimer could not be imaged,the surface morphology of G4 dendrimer films on mica at different surface densities was observed by AFM.