Figure 1. Structure and size comparison of polyamidoamine dendrimer. (a) Polyamidoamine (PAMAM) dendrimers, also known as "artificial proteins", with a well-defined structure, can act as a nanoprobe to probe specific surface domains on the surfaces of enamel crystals. Three types of PAMAM dendrimers, with amine-, carboxylic-acid-, and acetamide-capped surfaces, respectively, were used in this study. Tapping-mode AFM images of enamel crystals (control). (b) Enamel crystals on a mica surface, imaged in air prior to the introduction of dendrimers. (c) Enamel crystals on a mica surface, imaged in air after the sample (b) was rinsed with distilled water (pH 7.4) and dried in a desiccator. 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.