A team of researchers from North Carolina State University and Rice University has created UV light-driven, unimolecular ‘submarines’ that contain just 244 atoms.
Each of the nanomachines has a motor powered by UV light. With each full revolution, the motor’s tail-like propeller moves the machine forward 18 nm.
And with the motors running at more than a million RPM, that translates into speed.
“These are the fastest-moving molecules ever seen in solution,” said Prof. James Tour of Rice University in Houston, Texas, senior author of a study published this month in the journal Nano Letters.
The study proves molecular motors are powerful enough to drive the sub-10-nm submarines through solutions of moving molecules of about the same size.
“This is akin to a person walking across a basketball court with 1,000 people throwing basketballs at him,” Prof. Tour explained.
The motors of these nanomachines operate more like a bacteria’s flagellum than a propeller and 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 it 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 researchers explained.
For comparison tests, they made nanosubmarines with no motors, slow motors and motors that paddle back and forth.
All versions of the nanomachines have pontoons that fluoresce red when excited by a laser.
“One of the challenges was arming the motors with the appropriate fluorophores for tracking without altering the fast rotation,” said Victor García-López, a graduate student at Rice University and lead author on the study.
The researchers then measured how well their nanomachines moved. “We had used scanning tunneling microscopy and fluorescence microscopy to watch our cars drive, but that wouldn’t work for the submersibles. They would drift out of focus pretty quickly,” Prof. Tour said.
The team sandwiched a drop of diluted acetonitrile liquid containing a few nanosubmarines between two slides and used a custom confocal fluorescence microscope to hit it from opposite sides with both UV light and a red laser.
“The laser defined a column of light in the solution within which tracking occurred,” García-López said.
The team hopes future submersible nanomachines will be able to carry cargoes for medical and other purposes.