Rice University
scientists have created light-driven, single-molecule submersibles that
contain just 244
atoms. (Illustration by Loïc Samuel/Rice University)
(November 16, 2015) Speedy
single-molecule submersibles are a first
Though they’re not quite ready for boarding a lá “Fantastic
Voyage,” nanoscale submarines created at Rice University are proving themselves
seaworthy.
Each of the single-molecule, 244-atom submersibles built in
the Rice lab of chemist James Tour has a motor powered by ultraviolet light.
With each full revolution, the motor’s tail-like propeller moves the sub
forward 18 nanometers.
And with the motors running at more than a million RPM, that
translates into speed. Though the sub’s top speed amounts to less than 1 inch
per second, Tour said that’s a breakneck pace on the molecular scale.
A chemical
schematic shows the design of single-molecule nanosubmersibles created
at Rice
University. The sub’s fluorescent pontoons are blue; the motor is red.
(Illustration by
Victor García-López/Rice University)
“These are the fastest-moving molecules ever seen in
solution,” he said.
Expressed in a different way, the researchers reported this
month in the American Chemical Society journal Nano Letters that their
light-driven nanosubmersibles show an “enhancement in diffusion” of 26 percent.
That means the subs diffuse, or spread out, much faster than they already do
due to Brownian motion, the random way particles spread in a solution.
While they can’t be steered yet, the study proves molecular
motors are powerful enough to drive the sub-10-nanometer subs 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,” Tour said.
Rice graduate
student Victor García-López holds a vial with millions of single-molecule
nanosubmersibles.
The nanosubs consist of 244 atoms and have motors that turn
when activated
by ultraviolet light. (Credit: Jeff Fitlow/Rice University)
Tour’s group has extensive experience with molecular
machines. A decade ago, his lab introduced the world to nanocars,
single-molecule cars with four wheels, axles and independent suspensions that
could be “driven” across a surface.
Tour said many scientists have created microscopic machines
with motors over the years, but most have either used or generated toxic
chemicals. He said a motor that was conceived in the last decade by a group in
the Netherlands proved suitable for Rice’s submersibles, which were produced in
a 20-step chemical synthesis.
“These motors are well-known and used for different things,”
said lead author and Rice graduate student Victor García-López. “But we were
the first ones to propose they can be used to propel nanocars and now submersibles.”
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 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.