The team formed the nickel propellers¿each measuring some 750 nanometers long and 150 nanometers wide¿at the University¿s Nanofabrication Facility in a series of steps. First they used electron-beam lithography to define the structures on silicon wafers coated with polymethyl methacrylate (PMMA). Next they deposited the nickel using electron gun evaporation, and chemically removed any residual PMMA and nickel. They popped the propellers off the substrate by way of isotropic etching, and coated them with a thin layer of chemicals to help attach them to the rest of the device.

Source: EDWIN JAGER et al. NANO-ROBOT has an elbow, wrist and hand--with two to four fingers--that can grab, lift and move a 100-micrometer glass bead from one track to another. The joints, formed from bilayers of gold and conjugated polymer, bend when electrochemical oxidation or reduction makes the polymer undergo a volume change.

In fact, the propellers more or less self-assembled with the molecules of ATPase, which the group produced from genetically altered bacteria. The motor-propeller combination was then mounted on 200-nanometer high, 80-nanometer wide nickel posts, and immersed in a "fuel" solution of ATP and other chemicals. The ATPase broke atomic bonds in the ATP molecules, as it does in living organisms. But in this case, the reaction cranked a rotor-like protein inside ATPase, thereby spinning the propellers. When the scientists observed the hybrid motors using a charge-coupled device (CCD) video camera, they found that the propellers spun at a rate of roughly eight revolutions per second, in some cases continuing at that pace for two-and-a-half hours straight.

The devices and the tactics used to make them need improvement. Montemagno notes that of the first 400 assembled units, only five worked. In later batches, some of the motors lost their propellers and others, their test pedestals. Moreover, the team would like to make the devices friendlier for use among delicate organic molecules and living cells. They would like to strip away from the finished product more of the harsh chemicals used to make the propellers, and add computational and sensing functions. They would also like to find ways to fuel the biomolecular motors using light energy in place of ATP. Still, the work marks a major step.

Bending Plastics

Scientists from Link¿pings Universitet in Sweden and the University of Maryland have developed other potentially useful devices made from conjugated polymer actuators, which they review in the Science special section on nanotechnology. Edwin Jager, Elisabeth Smela and Olle Ingan¿s have worked with conjugated polymers for several reasons: First, these materials operate well in aqueous media¿and most biological samples are sampled and tested in liquids. Second, they can be patterned using standard photolithography. And they readily undergo volume changes (during oxidation and reduction reactions) that can be exploited to make them bend at a variety of angles: If you attach the polymer to, say, gold, only the polymer will change size, making the combined bilayer curl.

Source: EDWIN JAGER et al NANO-HAND, also made from bilayers of gold and conjugated polymer, can curl around a grain of sand.

Jager and his colleagues recently built and tested a tiny robotic arm, consisting of linked microactuators made from a bilayer of gold and polypyrrole, a particularly stable conjugated polymer. The arm, measuring a mere 670 micrometers long, had an elbow, wrist and hand, with two to four fingers. And by way of electrochemical oxidation and reduction, they were able to bend these separate "joints" so that the arm could grab, lift and move a 100-micrometer glass bead (see illustration). They envision such arms being used in tandem to transfer cells around on a lab-on-a-chip.

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