Letting Nature Be the Architect

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Sandhage's project isn't the first time researchers have used organic templates to produce nanoscale devices and materials. Angela Belcher, a professor in MIT's Department of Materials Science and Engineering, has used viral proteins to assemble a variety of materials, and a startup called Cambrios is pursuing commercial applications of her work.

Daniel Solis, a graduate student in Belcher's lab, is working on viruses that can attach themselves to gold electrodes and coat themselves with semiconductor material; eventually he hopes to use the viruses to make working transistors.

Diatoms could provide templates for many other types of structures -- but exactly what types is not yet clear. Sandhage hopes that the hundreds of thousands of examples of uniquely-shaped diatoms in nature will inspire engineers to consider new design possibilities for processors and memory chips.

Sandhage's colleagues are already learning about how diatoms' genes determine their shape, with the hope of allowing engineers to design diatoms to their own specifications.

The genome of one diatom species has been completely sequenced, and another is on the way. Mark Hildebrand, a molecular biologist at the Scripps Institution of Oceanography and partners with Sandhage, believes that the diversity of natural diatom shapes suggests, though counter-intuitively, that there are just a few core genes that control these shapes.

If there are only a few key genes, he says, then relatively few mutations would be required to cause the huge variety of existing shapes. Hildebrand hopes that identifying these genes and manipulating both the genes and the environments in which the diatoms grow up will allow researchers to create novel structures.

That's a hope seconded by Lucent Technologies' Joanna Aizenberg, who has produced tiny lenses inspired by the structure of sponges.

"Being able to understand the genetics -- how diatoms produce the variety of their forms -- may give us the way to produce non-natural forms using their genetic codes," says Aizenberg.

Sandhage cautions that engineering the diatoms and arranging them into useful structures for electronic devices is "not a trivial challenge." Aizenberg and Berggren say they agree -- but both are reservedly optimistic. 

"There may be limits to how arbitrarily they can engineer them," says Berggren. "[But] I think they're going to be able to engineer these diatoms to make different kinds of structures."

Meanwhile, Sandhage has already developed a couple of uses for his new structures, including using materials that catalyze chemical reactions as the coating for diatoms. The large ratio of surface area-to-volume in structures based on diatoms makes them into ideal catalysts when floating free in a solution, Sandhage says.

He has used catalyst-coated diatoms to destroy pesticides, a technique that might eventually be used to prevent the runoff of dangerous chemicals into streams and groundwater. He has also made photo-luminescent structures by coating diatoms with materials that glow under certain wavelengths of light. The structures could one day be used in computer displays.