Web Release Date: April 5,
Tapping Mode Atomic Force Microscopy Investigation of Poly(amidoamine) Dendrimers: Effects of Substrate and pH on Dendrimer Deformation
Departments of Chemistry and Physics and the Center for Biologic Nanotechnology, University of Michigan, Ann Arbor, Michigan 48109-1055
Received September 11, 2000
In Final Form: February 9, 2001
Abstract:
Substrate effects, volume reproducibility, and pH effects on the size and shape of ethylenediamine core poly(amidoamine) dendrimers (generations 6-9) were explored using tapping mode atomic force microscopy (AFM) measurements. A statistical analysis of the measurements indicated a 4% variation in volume for repeated measurement using the same tip. Volume determinations by numerical integration and a spherical cap estimation method were explored. The spherical cap model was shown to overestimate dendrimer volumes by a factor of ~2. As substrates were changed from mica to more hydrophobic surfaces, AFM-measured heights and diameters approached ideal-sphere dendrimer diameters. Acidification of dendrimer samples from generations 6-9 led to an observed 33% increase in volume, 26% increase in height, and 9% decrease in diameter. Expansion upon acidification can be attributed to maximization of charge separation and increased solvent retention within the dendrimers. Single dendrimer resolution within two-dimensional clusters was enhanced using carbon nanoprobes.
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