Rice University Scientists Create Nanoscale Submarines

Posted on November 21, 2015

Scientists at Rice University in the lab of chemist James Tour have created nanoscale submarines that are powered by ultraviolet light. The submersibles consist of a single molecule made of 244 atoms. The ultraviolet light motor has a tail-like propeller that moves the sub forward. The new subs are the fastest moving molecules ever seen in solution, according to Dr. Tour.

The subs don't have a steering mechanism yet, but the motors are powerful enough to propel the sub through solutions of moving particles that are the same size as the submersible. Tour explained it this way, "This is akin to a person walking across a basketball court with 1,000 people throwing basketballs at him." The motors can run at more than one million RPM, for a top speed of just under 1 inch per second which is extremely fast for molecules.

Over the years a number of researchers have created microscopic machines with motors. But most of those either use toxic chemicals to create the forward motion or have toxic chemicals as a byproduct of the motion. the Rice University researchers are the first to use these motors to propel nanocars and submersibles.

The motors complete each revolution in four steps. Light is used to excite the double bond that holds the rotor to the body, which then becomes a single bond. This allows the rotor to rotate one quarter step. Seeking to return to a lower energy state, the motor jumps adjacent atoms which creates another quarter turn. So long as the light is on, the motor keeps rotating and moving.

The researchers also created submersibles that have motors that paddle back and forth, motors that move slower than the main submersibles' speed of nearly one inch per second and submersibles with no motor at all. The submersibles all have pontoons that fluoresce red when they are excited by the laser.

The Rice team called in researchers at North Carolina State University to help them track the subs and how well they move. They normally used scanning tunneling microscopy and fluorescence microscopy to to watch the nanocar drive, but that method doesn't work for the subs. They drift out of focus too quickly.

To track the nanosubs, the scientists placed a drop of diluted acetonitrile liquid containing a few nanosubs between two slides. They then used a custom confocal fluorescence microscope to to bombard both sides with ultraviolet light and a red laser. The UV light targets the motor and the red laser targets the pontoons. The scientists could see one molecule at a time this way and track its movement.

The nanosubs have great potential in the medical and other fields, although the research is still in its infancy. Lead author and Rice graduate student Victor Garcia-Lopez said, "There's a path forward. This is the first step, and we've proven the concept. Now we need to explore opportunities and potential applications."

Garcia-Lopez's co-authors are Pinn-Tsong Chiang, Fang Chen, Gedeng Ruan, Angel A. Martí, Anatoly B. Kolomeisky, Gufeng Wang, and James M. Tour. The team's findings were published in Nano Letters. You can read more about the research here.

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