Single-Molecule Motor Spins 50 Times a Second--We Know; They Counted

Diagram of molecular motor setup from Sykes Laboratory at Tufts, showing the copper surface (orange), the LTSEM tip (grey), and the methylsulfanylbutane molecule, with spin direction indicated in green. [Image: Tufts University[
In the grand tradition of science interns throughout history, a handful of high schoolers, undergrads, grads, and post-docs spent months counting stuff. That’s not news: Interns were basically invented to fetch coffee and count things. But, as with (now-) famous interns Geiger, Marsden and Muller, counting stuff for months has paid off enormously: a team of Tufts chemistry researchers and their supporting interns has confirmed the feasibility of the smallest motor known to humankind.

The electric engine measures a single nanometer wide, 99.5% smaller than the previous tiniest-motor-ever record holder.

Conceived by Charles Sykes and tested by those counting interns, the motor is comprised of a single 18-atom asymmetric molecule called butyl methyl sulfide (or 1-methylsulfanylbutane, if you want to be IUPAC about it). The sulfur atom has two hydrocarbon arms, one of four carbons (butyl) and the opposite of only one (methyl).

When the sulfur atom is pinned to a surface (Sykes used copper) and charged, the electric energy is converted into rotational energy, which causes the little lopsided propeller to start spinning. That spin could eventually be used to direct liquids along microfluidic plumbing used in small-scale medical testing and other lab-on-a-chip applications.

There’s a long way to go before that point: The engine currently operates at temperatures around 5 Kelvin, and is given electric current by one of about 100 low-temperature scanning electron microscopes. To add to the fun, the researchers aren’t even sure why it works: there’s some anisotropy in spin caused by the orientation in which the molecule is pinned, but that could be due to any number of factors.

But the fact that the motor does work has been proven by Sykes and his team. Proving the motor’s efficacy meant counting how many times the motor spun per second, which meant interns--including some high-schoolers--analyzed five-minute chunks of data for weeks on end. It put them on a pretty good path, you might say, seeing as most pre-college kids are lucky to get their drivers’ licenses, let alone a Nature Nanotechnology article byline. Well-counted, all, and good luck with that Guiness World Records application.

[Tufts via New Science and Engadget]

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