Nanoscale characterization of nautilus shell structure: An example of natural self-assembly

Structural characterization at the nanometric scale of the Nautilus sp shell was carried out by high-resolution transmission electron microscopy and high-angle annular dark field to understand how the organic and inorganic components are related. The inorganic phase that built the shell is made of calcium carbonate (CaCO₃), with the orthorhombic unit cell of the aragonite, in a texturized arrangement in such a way that the c-axis is always perpendicular to the shell surface. The organic material forms films through the plates. We observed for a very first time some aragonite nanocrystals embedded in the organic matrix. This observation supports the hypothesis that the proteins and other organic compounds guide the crystal growth because the organic matrixes are the places where the nanocrystals grow.