Nanostructure of Diatom Silica Surfaces and of Biomimetic Analogues

Diatoms generate their cell walls by silica biomineralization. The cell walls are composed of silica and organic macromolecules and show a complex microscopic structure. Analysis of this structure by different atomic force microscopy (AFM) techniques revealed an unexpected nanostructured granular surface. Silaffins, proteins that are posttranslationally modified with long-chain polyamines, and oligo-N-methyl-propyleneamines were identified as the main organic constituents of diatom biosilica.1 Silaffins as well as free propyleneamines of different chain lengths induce rapid precipitation of nanosized particles from silicic acid solutions in vitro. In a biomimetic approach, we reacted aqueous silicic acid solution with tripropylenetetramine in CHCl3 in a biphasic system. As a result, thin nanostructured silica layers that show a granular nanostructure very similar to that of the diatom cell walls were obtained. This finding may serve as a good model to study the mechanisms that lead to the nanostructure of the diatom cell walls.