Rice University scientists have created light-driven, single-molecule submersibles that contain just 244 atoms. The motors of the "nanosubmarines" run at more than a million RPM, and the sub's top speed amounts to less than 1 inch per second.

"These are the fastest-moving molecules ever seen in solution,” said James Tour, a Rice lab chemist.

The motors, which operate more like a bacteria’s flagellum than a propeller, complete each revolution in four steps. When excited by light, the double bond that holds the rotor to the body becomes a single bond, allowing the device to rotate a quarter step. As the motor seeks to return to a lower energy state, it jumps adjacent atoms for another quarter turn. The process repeats as long as the light is on.

The light-driven nanosubmersibles show an “enhancement in diffusion” of 26 percent, meaning the subs spread out faster than they already do due to Brownian motion, the random way particles spread in a solution.

Rice’s researchers hope future nanosubs will be able to carry cargoes for medical and other purposes.

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