Imaging Single Nacreous Tablets with the Atomic Force Microscope

Abstract

ABSTRACTAfter describing some recent developments in atomic force microscopy (AFM), a specific application to the study of shell ultrastructure is examined in detail. By embedding bleached nacreous tablets in epoxy and imaging them with the atomic force microscope (AFM) during in situ dissolution, it was possible to visualize the topography of both the top faces of the tablets and the impressions in epoxy made by the bottom faces of the tablets. This epoxy imprint reproduced tablet features down to the 10 nm scale. Using this technique it should be possible to measure correspondence between topographic features on the proximal and distal faces of tablets, which is necessary to form a three-dimensional picture of the nacreous region. In addition to these dissolution experiments, growth experiments (in modified sea water) on bleached, embedded tablets indicated that aragonite grows on a tablet as asperities oriented along the c axis, normal to the tablet surface. No change was seen on the surface of the epoxy, which confirmed that the crystals were growing on the tablet surface, not spontaneously nucleating out of solution.