Atomic force microscopy studies of generation 4 poly(amidoamine) (PAMAM) dendrimers on functionalized surfaces

The aim of this work was to understand the factors effecting the interactions of generation 4 amino terminated PAMAM (G4 PAMAM) dendrimers with chemically functionalized surfaces. To this end, the adsorption of G4 PAMAM dendrimers onto model alkanethiol self-assembled monolayer surfaces terminated in methyl, carboxyl and amine functional groups was studied using the atomic force microscope (AFM). AFM images were obtained of all surfaces in air and in liquid, before and following dendrimer adsorption. The similarity of the features observed at both of these stages however, caused difficulties in their discrimination using AFM height images only. In situ imaging and force measurement (force–distance and amplitude–phase–distance) experiments were therefore performed to determine whether the imaged features originated from the PAMAM dendrimer molecules or the underlying functionalized substrates. Interestingly, force–distance and amplitude–phase–distance measurements obtained with carboxyl functionalized AFM probes suggested differences in the dendrimer conformation on the different alkanethiol surfaces.