Nanoscale Control of Silica Morphology During Diatom Cell Wall Formation

M. Hildebrand, E. York, J. I. Kelz, A. K. Davis, and L. G. Frigeri (Scripps Institution of Oceanography, University of California—San Diego), D. P. Allison (University of Tennessee, Knoxville), M. J. Doktycz (CNMS Staff)

Scientific Achievement

A unique approach that combines biological manipulation with advanced imaging tools was used to examine silica cell wall synthesis in the diatom Thalassiosira pseudonana. The innate capabilities of diatoms to form complex 3D silica structures on the nano- to micro-scale exceed current synthetic approaches because they use a fundamentally different formation process. Understanding the molecular details of the process requires identifying structural intermediates and correlating their formation with genes and proteins involved. In T. pseudonana, distinct silica morphologies were observed during formation of different cell wall substructures, and three different scales of structural organization were identified. A combination of electron and scanning probe microscopies were used. At all levels, structure formation correlated with optimal design properties for the final product. These results provide a measurements benchmark and new insights into biosilicification processes.

Significance

One of the challenges in material science is controlling the structure and morphology of inorganic materials. Biological systems excel in this regard and are capable of generating nano- and microstructured materials with precise yet diverse structural features. Further, they are capable of controlling material synthesis at low temperatures and mild reaction conditions. The unicellular algae known as diatoms produce complex nano- and microscale silica structures in their cell walls, reproduced with fidelity, inexpensively, and in enormous numbers through biological replication. Based on these recent advances, new insights into biomolecular-based synthesis of inorganic material are provided. Understanding these synthetic routes will aid in the development of approaches to controllably alter diatom structure and to develop bioinspired routes to material synthesis.

The results of this work are published in:
Hildebrand et al., “Nanoscale control of silica morphology and three-dimensional structure during diatom cell wall formation” J. Mater. Res. 21(10), 2689 (2006).

Doktycz’s participation was supported by the CNMS while the other investigators were supported by the Air Force Office of Scientific Research Multidisciplinary University Research Initiative Grant No. RF00965521. The AFM imaging of diatoms structures was performed in the CNMS-affiliated Biochemistry, Biotechnology and Nanobio research facility.

AFM images of the proximal (left) and distal (right) surfaces of the diatom T, pseudonana. The proximal surfaces shows a distinct beaded silica morphology that is in sharp contrast to the smooth silica that is observed on the distal surface. The development of these correlate to different stages of cell development and the expression of different proteins.