Diatom Wall Patterning

Example Patterns

Diatom Patterns (Scroll all the way to the bottom)

Specifications

	Theoretical	Empirical
Pixel Dimension		50 nm X 5 nm
Pattern Size		100 um X 100 um
Accuracy
Precision

Mechanism

The diatom cell wall is made up of silica. Silica formation occurs inside the silica deposition vesicle (SDV) within the diatom. The SDV has not been isolated yet but it is known that the SDV is acidic and contains orthosilicic acid Si(OH)4, long chain polyamines (LCPA), and 4 families of proteins. The SDV later becomes half of the daughter cell’s cell wall while the other half comes from the parent diatom cell wall(1, 2).

In the diatom species Thalassiosira pseudonana, silicification starts at the center and extends radially outwards(3). First the rim gets silicified followed by the rest of the wall and the nanopores. During the last step, the cell wall becomes rigid by silicification occurring in the z direction. It is thought that the silicification process at the nanoscale is organized into the microscale of the cell wall by the cytoskeleton.

The key components of silica patterning are Si(OH)4, LCPA, and a family of proteins called Silaffins. LCPA are (N-methylated-) poly(propyleneimine). Silaffins are peptides with many serine and lysine residues to bind to LCPA. When you mix LCPA and Silaffins in a silicic acid solution, silica precipitates into solid spheres.

Hypothesized Mechanisms of nanopatterning silica:

1. Diffusion-limited phase separation(4)

LCPA is able to form microdroplets within the SDV in a hexagonal close packed arrangement. The interface between the LCPA droplets contains silica. Precipitation of silica occurs at the interface in a diffusion-limited manner to create a honeycomb like framework.

2. Silaffin and LCPA mediated aggregation(5)

Silaffin and LCPA catalyze precipitation of silica. The same Silaffin peptide catalyzes another reaction creating a network of precipitated silica particles.

3. Organic matrix template