Figure 3. Tapping-mode AFM images of enamel crystals after interaction with carboxylic-acid-capped PAMAM dendrimers. A solution containing G7 PAMAM dendrimers with carboxylic-acid (-COOH)-capped surface was allowed to flow over the crystals and allowed to remain for 2 min before being wicked off. The sample was dried in a desiccator before being imaged in air. (a) Crystal surfaces after exposure to 1 µL 570-nM dendrimer solution (arrows denote dendrimers at crystal interface). (b) Crystal surfaces after exposure to 1.5 µL 285-nM dendrimer solution (arrows denote dendrimers on crystal surface). (c) Crystal surfaces after exposure to 2 µL 570-nM dendrimer solution. (d) After sample (c) was rinsed with distilled water (pH 7.4). (e) After sample (d) was rinsed with 100 mM phosphate buffer (pH 7.4). AFM images show the topographical image (1 µm x 1 µm) on the left, and phase image (1 µm x 1 µm) on the right.