Time-lapse video of the network being built, with tracks in red, and the fluorescent dye "cargo" in green. Scale is 10 micrometers. Via Oxford
British researchers have made something like the tiniest train set ever, built out of proteins and synthetic DNA. Developed by scientists at Oxford University and Warwick University, the nanoscale transport network is self-organising: it can construct its own tracks, carry cargo across them, and dismantle itself.
“One of the more sci-fi visions of nanotechnology is the creation of moving ‘nanobots,' but it turns out that nature got there first,” lead researcher Adam Wollman told me in an email. “In each of your cells an army of nanoscale motor proteins transport cargo around the cell on a network of tracks called the cytoskeleton. So instead of building our own, we wanted to harness one of these motor proteins, specifically one called kinesin, and attempt to control it.”
They made two different types of nano machine: “assemblers,” which built the track, and “shuttles,” which carried cargo—in this case, fluorescent green dye—along the tracks. By fusing the kinesin to DNA nanostructures, they were able to tell it what to do via different DNA signals. For example, when they introduced ATP (adenosine triphosphate, which acted as fuel) into a mix of assemblers and microtubules, the assemblers formed tracks out of the microtubules. The researchers then sent cargo-carrying shuttles along the tracks, and could use other signals to make the shuttles huddle together at the circular track’s centre or release their cargo into the environment.
A photo from Wollman shows what the microtubule "tracks" actually look like: "The microtubules are in white and the image is 50 microns across (1/20th of a millimeter)."
Wollman explained that the train analogy comes from the way the proteins move. “You might think that the best way to move in the water filled environment of the cell is to swim, but actually, at the nanoscale, this is very inefficient,” he said. “These proteins actually move by walking with two protein feet along a straight track called a microtubule.” However, the tracks looks less like train tracks and more like the spokes on a bike wheel, arranged around a central point.
The nanotrain work was published in Nature Nanotechnology, and is a step on the way to developing more sophisticated self-assembling systems. Wollman explained it could also have a range of applications if the dye cargo were replaced with other compounds.
“The nanotrains concentrate their cargo into a tight space at the centre of the network, and we wondered if this could be used to gather the components for chemical reactions, speeding them up, or maybe to help detect very dilute chemicals in a biosensor by concentrating them,” he said.