Tapping mode atomic force microscopy investigation of poly(amidoamine) dendrimers: Effects of substrate and pH on dendrimer deformation

Theodore A. Betley, Mark M.Banaszak Holl, Bradford G. Orr, Douglas R. Swanson, Donald A. Tomalia, James R. Baker

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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.

Original languageEnglish
Pages (from-to)2768-2773
Number of pages6
JournalLangmuir
Volume17
Issue number9
Publication statusPublished - 1 May 2001
Externally publishedYes

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