Engineers have created metallic nanofish that are inspired by the swimming style of real fish, and could be used to carry drugs to specific sites of the body.
The nanofish are 100 times smaller than grains of sand, and are constructed from gold and nickel segments linked by silver hinges. The two outer gold segments act as the head and tail fin, while the two inner nickel segments form the body. Each segment is around 800 nano-meters long, a nano-meter being one billionth of a meter.
When an oscillating magnetic field is applied, the magnetic nickel parts move from side to side. This swings the head and the tail, creating an undulating motion that pushes the nanofish forward. Speed and direction can be controlled by altering the strength and orientation of the magnetic field.

The nanofish were developed by Jinxing Li at the University of California, San Diego, and his colleagues, who are now investigating potential medical applications.
“We believe they could be useful for medicine delivery, non-invasive surgery, and single cell manipulation,” says Li. External magnets could be used to direct drug-loaded nanofish to particular areas of the body, he says.
“This is an exciting new idea,” says Justin Gooding of the University of New South Wales, Australia. “A lot of work on drug delivery vehicles relies on the body’s transport systems to move the particles to the site of the pathology.”
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“However, active transport has recently begun to be explored and this work shows that active transport particles can be made smaller and faster,” he says.
Several other research groups are also developing ‘nanoswimmers’ for drug transport. Most of these use helical propellers inspired by the corkscrew tails of bacteria, but experiments have shown that the propulsive mode of nanofish is more efficient.
One major question that remains is how to remove the nanofish from the body after use. Li says the team is now working on developing biodegradable versions, so that the metal does not get stuck inside the body.