Eating Carbon Nanotubes

Fathi Moussa

Lon Wilson

Last year I covered Khodakovskaya et al.’s paper regarding the benefits of growing tomatoes in carbon nanotubes (CNT).^[CB] At the time I was concerned with the potential health risks associated from eating carbon nanotubes, but today in ACS Nano my concerns are alleviated. A paper from Lon Wilson’s and Fathi Moussa’s research groups discusses the effects from administering oral doses of carbon nanotubes (concentrations as high as 1g of CNT per kg body weight) to Swiss mice.^{[ACS Nano]} The authors summarize their work the best.

CNT materials did not induce any abnormalities in the pathological examination. Thus, under these conditions, the lowest lethal dose (LD_Lo) is greater than 1000 mg/kg b.w. in Swiss mice.

So feel free to eat all the CNTs you want in lab, assuming they are not functionalized, you do it only once, and you limit yourself to single walled carbon nanotubes. I think partly because the results of the oral administration of CNTs went without any interesting side effects to present, the authors also looked into what happens when you inject CNTs into the peritoneal cavity of mice.

The image on the left is the control while the image on the right is 14 days after injecting mice with CNTs at a concentration of 1g CNT per kg of mouse. Although it looks sickly, the mice injected with the high concentration of CNTs did not die. Well…, not from the CNTs anyways.

Link to paper: In Vivo Behavior of Large Doses of Ultrashort and Full-Length Single-Walled Carbon Nanotubes after Oral and Intraperitoneal Administration to Swiss Mice (ACS Nano)

Mitch

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Linear-Motor from Carbon Nanotubes

A recent paper this week by Somada et al. regarding making a linear-motor from carbon nanotubes piqued my interest.^[NanoLett] The general design idea is to encapsulate a piece of carbon nanotube material within a larger carbon nanotube. If done correctly you can end up with a configuration as shown below.

The cargo, in yellow, transverses the carbon nanotube and rests in either position A or position B. An abridged summary of their observations is as follows: 1) From observing the system for 170 s the cargo traveled back-and-forth seven times; 2) The cargo was never filmed in between positions A and B, indicating the movement was less than the frame rate (0.5 s). From this information I can construct a likely energy landscape for this system.

Mitch’s hypothetical potential energy map for the linear-motor.

The diagram replicates the observation that the cargo at room temperature will be trapped at either position A or B. It also explains why it’s never seen between A or B, as there is no energy minimum for it to rest in. Lets assume every ~20 s there is randomly enough thermal energy to kick the system over the barrier, and that this accessible energy exists for less than 0.5 s. Then you would expect the cargo to be able to move either to A or B, and to do it faster than the shutter speed.

This is an interesting system for analysis, but it’s not a motor. Or conversely, it is as much a motor as ethane is a useful rotor. Just because thermal energy provides the means for things to happen it doesn’t mean it generates usable work. There is no way to construct a usable motor or any device from this system, but it’s a first step in that direction. I suspect if the authors raised the temperature they would see the cargo undergoes random walk motion. Thermal energy yields a random linear-motor.

Link to article: A Molecular Linear Motor Consisting of Carbon Nanotubes

Update 1: Tim Reid also covered it at Nature Chemistry — Nanotube motors: Sliding and spinning

Mitch

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