Researchers have built what they claim is the world’s tiniest engine — just a few billionths of a metre in size — as a step towards nano-machines that could navigate in water, sense the environment around them or even enter
living cells to fight disease.

The prototype nano-engine — powered by light — is made of tiny charged particles of gold, bound together with temperature-responsive polymers in the form of a gel.

When heated to a certain temperature with a laser, “it stores large amounts of elastic energy in a fraction of a second, as the polymer coatings expel all the water from the gel and collapse”. This has the effect of forcing the gold nano-particles to bind together into tight clusters. “When the device is cooled, the polymers take on water and expand, and the gold nano-particles are strongly and quickly pushed apart, like a spring”. The results are reported in the PNAS journal.

Tao Ding from Cambridge’s Cavendish Laboratory (the paper’s lead author) said: “It’s like an explosion. We have hundreds of gold balls flying apart in a millionth of a second when water molecules inflate the polymers around them.” Study co-author Ventsislav Valev, now based at the University of Bath, said: “We know that light can heat up water to power steam engines, but now we can use light to power a piston engine at the nano-scale.”

Professor Jeremy Baumberg from the Cavendish Laboratory, who led the research, has named the devices actuating nano-transducers (ANTs). “Like real ants, they produce large forces for their weight,” he said.

“The challenge we now face is how to control those forces for nano-machinery applications.” The team is currently working with Cambridge Enterprise and several other companies with the aim of commercialising this technology for micro-fluidics bio-applications.