Scientists have developed the world’s tiniest engine -just a few billionths of a metre in size -which is powered by light and may help develop nano-machines that can navigate in water, sense the environment around them, or even enter living cells to fight disease.The prototype device is made of tiny charged particles of gold, bound together with temperature-responsive polymers in the form of a gel, reports BBC.When the ‘nano-engine’ is heated to a certain temperature, it stores large amounts of elastic energy in a fraction of a second, as the polymer coatings expel water from the gel and collapse. ‘Now we can use light to power a piston engine at the nanoscale,’ said Ventsislav Valev, now based at the University of Bath.