Speedy single-molecule nanosubs powered by UV light

A rendering of one of the nanosubmarines – the bit that's whipping at the bottom is its propeller(Credit: Loïc Samuel/Rice University​​)

For some time now, we've been hearing about the attempts by various groups to develop so-called nanosubmarines. Among other things, these microscopic "molecular machines" could conceivably be used for applications such as targeted drug delivery within the human body. Recently, scientists at Houston's Rice University created nanosubs that move at a "breakneck pace" when exposed to ultraviolet light.

Created in the lab of chemist James Tour, each of the tiny submersibles are made up of 244 atoms contained within a single molecule. Sticking out at the end is a tail-like propeller that works like a bacterium's flagellum, in that it creates propulsion by whipping back and forth.

In order to get that tail to move, the nanosubmarine requires exposure to UV light. When this happens, the double bond that holds the propeller onto the sub becomes a single bond, causing the prop to rotate a quarter-turn. As soon as this has happened, the propeller attempts to revert to a lower energy state, jumping past adjacent atoms to move another quarter-turn. This process goes on as long as the UV exposure continues, with the tail continuously moving at over 1 million RPM.

Each full four-step rotation moves the sub forward 18 nanometers through an acetonitrile liquid medium, attaining a speed of one inch per second. That reportedly makes them "the fastest-moving molecules ever seen in solution," at a speed which is 26 percent faster than that at which particles ordinarily disperse through a solution.

Additionally, the sub-10-nanometer sub manages this speed while pushing its way through moving molecules of roughly its own size.

In lab tests, the nanosubmarines were driven by UV laser light, which could conceivably penetrate through biological tissue. Although there's still no way of steering the subs, the researchers are pleased with what they've achieved so far. "This is the first step, and we've proven the concept," says graduate student Victor García-López. "Now we need to explore opportunities and potential applications."

A paper on the project was recently published in the journal Nano Letters.

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