Holy Fantastic Voyage, Batman. A team from Rice University has developed single-molecule nanosubmarines that could eventually be used to deliver medicines directly inside the body.
Back in 2006, this same group developed nanocars—a single-molecule vehicle with four wheels, axles, and independent suspensions that could be “driven” across a terrestrial surface. Unfortunately, many of the nano-scale devices developed since then either required or emitted toxic chemicals. Several years ago, however, a new motor developed by a group in the Netherlands caught the attention of Rice chemist James Tour, who applied it to his new nanosubmarine.
The new Unimolecular Submersible Nanomachines (USNs) consist of 244 atoms that, when bound together in a particular formation, comprise a single-molecule device that’s powered by ultraviolet light. With each full revolution of the sub’s tail-like propeller, the device moves forward 18 nanometers. The motors run at more than a million RPMs, allowing for a top speed of slightly less than one inch per second.
Now, that may not sound very fast, but as noted by Tour, that’s a wicked pace down at the nanoscale. As he noted in a Rice release, “These are the fastest-moving molecules ever seen in a solution.” The details of this study can now be found at Nano Letters.
The motors are more like a bacterium’s flagellum than a propellor. After the molecule is excited by light, the double bond that holds the rotor to the body transforms into a single bond. This allows it to rotate a quarter step. Then, as the motor naturally tries to return to its resting state, it jumps yet again for another quarter turn. This process is repeated so long as the light remains on.
Technically speaking, the devices display an “enhancement in diffusion” of 26%, which means the nanosubs spread out much faster than they would from Brownian motion alone, i.e. the random way that tiny objects diffuse in a solution. Unfortunately, the subs cannot be steered, but the research shows that the molecular motors are capable of traveling through solutions of moving molecules of roughly the same size.
Tour says this is a akin to a person being able to walk across a basketball court while 1,000 people throwing basketballs at them.
Looking ahead, the team hopes more sophisticated versions of the nanosub will carry cargoes for medical and other purposes. “There’s a path forward,” noted study co-author Victor García-López. “This is the first step, and we’ve proven the concept. Now we need to explore opportunities and potential applications.”