Magnetic nanorods on cruise control

Chemists have created miniature engines out of nanoscale metallic rods that propel themselves using chemical energy. The technology might one day yield new kinds of sensors or even tiny machinery for assembling nanodevices.

Each rod, about 1.5 micrometers long and 400 nanometers wide, consists of multiple segments of platinum, nickel, and gold. When the filaments’ makers at Pennsylvania State University in State College added them to an aqueous solution of hydrogen peroxide, the platinum segment, located at one end of the rod, broke down the hydrogen peroxide, releasing oxygen. The oxygen, in turn, weakened the attraction between the water molecules at that end of the nanorod. That opened the way for the rod to advance through the water, platinum end first.

For objects this small, water is highly viscous, explains Ayusman Sen of Penn State. Without a break in surface tension, “it would be like swimming through molasses,” he says.

The rods move through the water at a rate of 10 µm per second, says Sen. That’s about as fast as a bacterium that propels itself forward with a tiny, whiplike tail. “We raced the nanorods against the bacteria,” says Sen. It was a tie.

The two nickel segments within each rod are magnetic, and that enabled the researchers to control the rods’ direction of movement. When exposed to a magnetic field, the rods moved perpendicular to it.

The next step will be to attach a nanorod to a device, such as a biosensor searching for viruses, to speed up detection. The researchers describe the roving nanorods in the Jan. 21 Angewandte Chemie.

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