Nanotechnology in Nature: Ancient Algae Hints at Earth’s Past, Nanotechnology’s Future

Think big, multicellular animals – such as fish, humans, crabs or insects – are the only ones with skeletons? You’re wrong.

Around the time when dinosaurs were roaming the Earth, a unique breed of single-celled algae evolved a hard silica internal structure. This type of algae – called a diatom – was so successful that it has spawned as many as 100,000 currently surviving species, which populate both marine and freshwater environments. And through millions of years of evolution, these single-celled organisms left behind a multitude of hard, internal skeletons, which are both providing clues to our planet’s geologic past, and providing daring nanotechnology engineers with ideas of how to coax biology to build nanostructures for us.

A light microscope image of numerous diatoms. As is evident from the image, they can vary widely is size and shape. However, one of the defining characteristics of the organism is that they each grow a silica internal structure protecting it's internal components.

Mary Ellen Benson, a doctoral candidate with the Department of Geological Science at the University of Colorado-Boulder, is one researcher using diatoms found in ancient lakebeds to help paint a picture of North America’s geologic past. Her research involves cataloging and analyzing potentially dozens of varieties of diatoms unearthed from a now-dead lake located within the Florissant Fossil Beds National Monument in south-central Colorado.

“The lake existed during the late Eocene, about 34 million years ago,” Benson said. “The duration of the lake has been estimated at between 2,500 and 5,000 years.”

Benson uses a 1,000 power light microscope and a Scanning Electron Microscope – or SEM – to view and accurately image the silica shells that these ancient organisms left behind. These shells are typically just 3 or 4 microns across, and many of their unique or ornate features are just a couple nanometers in size. Depending on the type and variety of diatom skeletons she finds, more can be said about what kind of lake once existed in this now mountainous region, and how it came into existence.

“The diatoms can help us to tell whether the lake was saline or fresh,” she said. “Many of the genera found in the Florissant deposit exist today in freshwater environments.”

“The structure of the diatom internal skeletons, called ‘frustules,’ can vary widely and be quite beautiful,” Benson said. “They are made up of two parts of nearly equal size and shape, called ‘valves,’ that fit together like a pillbox. They are variously ornamented, and their walls are perforated by dozens of minute holes.”

“Diatoms include forms that are planktic, floating, and benthic, attached, having limited independent means of mobility; although some secrete slime through a slit in the valve to propel themselves along surfaces,” she said.

One of the hard, silica shells imaged by Benson using a Scanning Electron Microscope. This one looks something like a wheel, and has rested in the dried-up Colorado lake since the Eocene epoch.

Since all of the diatoms Benson has found are similar to existing freshwater species, this suggests that the ancient Eocene lake was similar to modern freshwater lakes.

“The evolution of freshwater diatoms and their expansion into new habitats over geologic time are subjects that are not very well understood,” she said.

“These are some of the oldest freshwater diatoms known,” Benson said.

Already, at least 25 different types of diatoms have been identified from this site.

“As diatoms are very sensitive to their environmental conditions, they can tell us a lot about water salinity, acidity, depth and flow in extremely ancient water bodies,” she said. “In formerly glaciated terrain, changes in fossil diatom communities brought about by the influx of glacial melt-water signal periods of climate fluctuation.

“In modern environmental studies, there’s a huge emphasis on collecting diatoms from rivers and lake systems to track changes in water quality,” Benson said.

So, from a geologic perspective, diatoms may have a lot to teach us about the Earth’s past. Biologically, these tiny organisms may also be more important than one might think, accounting for approximately 25 percent or the world’s net primary production. Not only that, but technologically, diatoms could ultimately play a major role in the future of electronics or even micro-electro-mechanical devices – or MEMs.

For many engineers, the longtime dream of nanotechnology has been to get biologic organisms to build structures for them, on the nano-scale. Diatoms look to be one of the more likely tools by which this dream may soon become a reality.

Another silica shell left behind from a dead diatom. This one contains dozens of tiny holes, each just a few nanometers across. The dream of many engineers is to use similar structures created by diatoms for various electric or mechanical purposes.

According to research conduced by scientists at the University of Manitoba, the complex silica structures grown by diatoms could be used as nanometer-sized silicon wafers in electronics, if only the microorganisms could be convinced to build the right structures.

Modern microchips are fabricated with lasers. A laser of a very specific wavelength is used to carve a complex circuit into a silicon substrate; then another silicon layer is added to the first, with the next dimension of the circuit carved into it. So, these silicon layers are added together, one-by-one – like stacking slices of bread – until, finally, a three-dimensional circuit is created. This process is tedious and very labor-intensive.

Diatoms may provide a way around this.

Oceanographer Ginger Armburst of the University of Washington was successful in sequencing the entire genome of one particular species of diatom in 2004 – her findings were published in the journal Science. One of the possible products of this research is that analyzing the genes in this single-celled organism may help engineers and biologists to selectively evolve them, so that specific silica structures can be made prevalent in laboratory populations.

The advantages of, essentially, breeding diatoms are that they automatically build these tiny silica structures in three dimensions – thus, avoiding the tedious laser lithography process – and that they can do this with minimal interference from scientists or engineers. In other words, if the right silica species could be created, then nano-chips would basically grow themselves.

Similarly, many engineers working with micro-electric-mechanical structures imagine a future in which the components for their minuscule machines are grown by diatoms.

Overall, since diatoms already build such complex structures on the nano-scale, they represent a very attractive and promising way for engineers to bypass the clumsy fabrication techniques already in existence – taking the science of small out of human hands and into the hands of microorganisms.

Related Sites

• algae: internet encyclopedia article
• silica: internet definition and basic properties
• diatom: University of Indiana Diatom Homepage
• microorganism: internet encyclopedia article
• nanotechnology: NCF News Page with definition
• eocene: UC Berkeley definition
• scanning electron microscope: NCF description
• micron: internet encyclopedia article
• frustules: digital image gallery definition
• pillbox: internet encyclopedia article describing WWII bunkers, often called pillboxes
• planktic: online definition
• benthic: online definintion
• MEMs: MEMs Exchange Homepage
• Diatoms growing structures : news article about the many used of diatoms

Further Information for Students or Professionals

• Mary Ellen Benson: Department profile
• Geological Science: Department Homepage
• University of Colorado: University Homepage
• Florissant Fossil Beds National Monument: Homepage
• University of Manitoba: Copy of the research findings
• Ginger Armburst : article published in SCIENCE

Selected Publications

1. Benson, M.E., Smith, D.M, and Spaulding, S.A., 2006, Exceptional Diversity in Late Eocene Freshwater Diatoms from the Florissant Formation, Teller County, Colorado: Geological Society of America Annual Meeting, Abstracts with Programs, 38(7), October 22-25, Philadelphia, PA.
2. Motzer (Benson), M.E., 1980, Paleoenvironments of the Lower Lakeview Limestone (Middle Cambrian), Bonner County, Idaho: unpublished M.S. Thesis, University of Idaho, Moscow, 174 pp., 6 pl.
3. Motzer (Benson), M.E., 1980, Middle Cambrian Faunas from Northern Idaho: Northwest Science Program and Abstracts, 53rd Annual Meeting of the Northwest Scientific Association, March 27-29, at University of Idaho, Moscow, p. 33.

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