Monday, April 30, 2007

Tiny Machines Made of Microbes

Fossilized silica shells of diatom algae
Enlarge picture

Biomimetics employs organisms as models for building new machines.

But now new machines could be made of organisms. In fact, tiny machines from microorganisms.

The single-celled Spirostomum, a Paramecium-related protozoan, resembling a tiny brown worm, can contract its 0.5 mm-long body to 25% of its length

in a millisecond: this is the fastest known movement in a microorganism.

Many microorganisms are integrated in MEMS (Microelectromechanical Systems) technology, the so-called “biotic-MEMS,” developing micron-level machines.

A team of University of Washington has realized a catalogue of the most promising microorganisms (all less than 1 mm long and made of one or few cells) for MEMS systems, and which can boost the conventional MEMS technology. “Tools and concepts have been increasingly borrowed from biology to solve technology problems. Biological concepts such as self-assembly are under serious consideration by technologists now for making highly integrated nano and micro systems”, said co-author Babak Parviz, an electrical engineer.

The microorganisms were assigned into four employment fields: material synthesis, precise structure formation, as functional devices, and integrated into controllable systems. Through biomineralization, a process detected in 700 million years old rocks, microorganisms can produce at least 64 different inorganic materials employed in MEMS technology, like silicon dioxide, biogenic calcite, magnets, gold and silver crystals.

Magnetic bacteria produce magnetosome crystals, crucial for the heading of their water movements.

Unlike industrial MEMS synthesis methods, requiring high temperatures, corrosive gases, vacuums and plasma, microorganisms produce the materials at room temperature, at near-neutral pH, in water solutions.

These structures made by microbes can develop into three dimensions and can be changed with nanoscale or macroscopic (visible scale) precision.

The spicules in the skeleton walls of one deep-sea sponge have excellent fiber-optical properties.

The fields of the chemical and biological sensors (for food and environmental monitoring) could employ microorganisms, as they evolved to detect specific chemicals. “One of the most interesting applications of MOs [microorganisms] in MEMS is to directly use them for detecting chemicals. MOs can be genetically engineered to have various receptors. All the transduction and amplification machinery is already in MOs. I think integration of these MOs into MEMS platforms can generate extremely powerful chemical/biological analysis systems”, said Parviz.

There are microbes that turn chemical energy into electrical energy, like the environmentally-friendly Microbial Fuel Cells for powering robotics and biomedical devices, and for economic hydrogen production, replacing small conventional batteries.

The biggest challenge by now is to integrate these devices into controllable micron-scale systems. “Our ability to manipulate small organisms and produce platforms that can interface with them one cell at a time is brand new. It is yet to be seen how researchers will take advantage of these new capabilities”, Parviz added.
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