World's Tiniest Engines Could Power Microscopic Robots

Scientists have created the world's tiniest practical engines, and these light-powered machines could one day power microscopic robots small enough to enter living cells, the researchers say. As technological innovations make devices smaller and smaller, scientists are developing machines that are only the size of complex molecules — nanometers, or billionths of a meter, in scale. In comparison, the average human hair is about 100,000 nanometers wide. One of the main reasons "nanobots" remain in the realm of science fiction is that figuring out a way to make them move has been challenging. Researchers have tried using a variety of power sources and propulsion systems for nanotechnology, but these typically lack speed, strength and control. "There have been many small machines, but they operate incredibly slowly — taking many seconds or minutes to move a single arm, for instance — and with very low forces," said Jeremy Baumberg, director of the University of Cambridge's NanoPhotonics Centre and senior author of the new study. "This is why we don't have nanobots, although they are much discussed in fiction." Nanobots require powerful forces to move because the viscosity of fluids can increase dramatically on the nanoscale. "For a nanomachine floating in water, swimming is like us swimming in a pool of treacle [a blend of molasses, sugar and corn syrup] — very, very viscous — so you need very large forces to move," Baumberg told Live Science. The new engines are made of tiny particles of gold only 60 nanometers in diameter. These particles are connected to one another by a water-laden gel made of a heat-sensitive compound. When heated by a green laser to more than 95 degrees Fahrenheit (35 degrees Celsius), the gel expels water, contracting within a microsecond and forcing the gold nanoparticles into tight clusters about 400 nanometers wide. When the engine is cooled, the gel takes on water and expands, and the gold nanoparticles are strongly and quickly pushed apart, like a spring, the researchers explained.