A genetically engineered bacteria was the donor of a virus-sized enzyme acting as a biological "motor." The researchers mounted the motors on a substrate bathed in adenosine triphosphate (ATP) — the fuel used by living cells — and attached submicron metal propellers, some of which spun for several hours during the demonstration.

"We believe we are defining a whole new technology — hybrid nanodevices can now be assembled, maintained and repaired using the physiology of life," said professor Carlo Montemagno.

Working with Montemagno on the device was Cornell professor Harold Craighead and Cornell researchers George Banchand, Hercules Neves and Anatoli Olkhovets. The device was constructed at the Cornell Nanobiotechnology Center.

The Cornell researchers describe themselves as "nanobiotechnolgists" attempting to merge living systems with fabricated inanimate materials, such as metal and silicon, at the submicron scale. Their tool kit includes custom-designed living organisms resulting from genetic engineering equipment, and custom-designed microelectromechanical systems (MEMS) built with silicon wafer fabrication equipment. The two are married at the submicron level where genetically engineered living organisms measure from 10 nm to 1 micron and tiny propellers, for instance, measure from 150 to 750 nm.

Nano-sized nurses

Inside every living cell, mechanical motion is powered by the chemical ATP, which is synthesized from sunlight and food in plants and animals. An enzyme called "ATPase" manufactured by a genetically altered Bacillus bacteria has the ability to transform ATP chemical fuel into kinetic energy by spinning in place. By chemically coding the pinnacle of the enzyme to match the shaft of the tiny inanimate propellers, the Cornell researchers were able to coax the self-assembly of hybrid living/inanimate systems — namely, propellers spinning at eight revolutions/second atop a living enzyme.

"We think our demonstration heralds a new generation of ultrasmall, robotic medical devices, what we call 'nanonurses,' because they could, for example, move throughout the body ministering to its needs, such as precisely dispensing drugs only to cells that need it," said Montemagno.

The metal propellers were manufactured at the nearby Cornell Nanofabrication Facility using electron gun evaporation, e-beam lithography and isotropic etching. The propellers attached themselves automatically using thin coatings of chemicals, which matched the ATPase enzymes, which in turn were attached to the pinnacles of 200-nm-high pedestals on the substrate. The whole device was then submerged in ATP.

During the demonstration only one out of every 80 pedestals succeeded in self-assembling a working motor-propeller system. Some propellers flew off of others, while some motors fell off their pedestals, and the rest never assembled in the first place. Nevertheless, the demonstration was deemed a success because some of the motors operated for the entire two-and-a-half-hour demonstration.

"We have a lot of challenges to meet and overcome, such as preventing these tiny parts from clumping together, but this demonstration shows that our concept is sound," said Montemagno.

Next researchers must work refining the self-assembly process and ensuring that all caustic chemicals present during fabrication have been neutralized.

For the future, Montemagno hopes to harness light energy to directly power hybrid living/inanimate devices that take up residence inside human bodies. By marrying biological sensors with inanimate computational devices, Montemagno hopes to create nanosized "nurses" small enough to fit inside a living cell, monitoring its activities and relaying that information outside the body.