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Don't let carbon nanotubes get all the hype! Carbon nano-onions might be the future of medicine and electronics and they just got much easier to make.

thumbnail: Takashi Shirai from NITech, Japan
by: Hank Green (he/him)

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No Nanodiamonds? Use Fish Scales!
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Head to to learn  more and for a 14-day free trial. [ ♪ intro ] Carbon nano-onions are not the  latest trend in molecular gastronomy. They are tiny nested balls of carbon  atoms that have incredible potential for the future of medicine and electronics.

They could be used in everything from  next-gen solar panels to glucose monitors. These tiny structures were  first observed back in 1980, when scientists were experimenting  with carbon nanostructures, and instructions on how to make  them were published in 2006. But if they’re so important, why  aren’t they everywhere by now?

Well, they ended up being really hard to make. And if they’re hard to  make, they’re hard to study, to make sure that they can  be used in all these really cool ways. But in 2022, one team of scientists  figured out a relatively simple way to create a bunch of high quality  nano onions in just seconds, And you're not going to believe how they did it! they microwaved fish scales.

Carbon atoms are great at bonding with  each other in a bunch of different ways, producing pure carbon compounds with different  atomic patterns and different properties. Graphite and diamonds are probably the two most  well known of these carbon allotropes, but there are more exotic ones, too. Graphene is just a sheet of  carbon that is one-atom thick.

And if you roll that sheet up into a tube, you get a carbon nanotube, which can be used everywhere from the  blackest of black paints to the cables of, for now, hypothetical space elevators. Nano-onions, meanwhile, are the  ogres of exotic carbon allotropes. They’re all about the layers.

Each core is made from a  hollow ball of 60 carbon atoms. Then that ball is encased  in a larger ball,   which is encased in another,  and another, and so on. Some nano-onions can have up to 50 layers!

And having those layers gives nano  onions a few different properties. Since the carbon atoms are forced into forming  smaller and smaller spherical structures, each layer tends to have defects  and holes in its structure. Those imperfections actually create more places  for chemical reactions to take place including sticking extra atoms or molecules onto  the layers, to give them different kinds of jobs.

A lot of those jobs take advantage of how well  carbon nano-onions conduct an electric charge,   and the fact that they’re stable  at a wide range of temperatures.   Since they can also store  energy and resist corrosion,   scientists want to use them as  capacitors in batteries and fuel cells.   But they’re also pretty transparent, which  makes them ideal for new types of solar cells.   In terms of medical applications,   scientists have proposed ways that they  could be used as electrochemical sensors, to eventually help detect the  levels of certain enzymes, or molecules like glucose. But their tiny size and non-toxic nature makes them perfect for targeted drug delivery, too. They can pass through parts of the body where  normal medication might struggle, like the barrier between the bloodstream and the brain.  And with all those built-in layers, the onions could deliver  time-release doses, too!

But even though nano-onions were  discovered at the same time as nanotubes, they’ve kind of fallen  behind in the research race, because they turned out to  be harder to manufacture. So far, the usual way requires heating  nanodiamonds to over 1600 degrees Celsius in a vacuum chamber, but that  takes a lot of time and energy. Other methods use harsh chemicals  or complex catalysts,   which are intermediary chemicals that help reactions along.

But the resulting onions still  might not be ready for practical use. Scientists often need to pop on these  little molecules called functional groups. Without them, the onions have a really hard  time dissolving and dispersing in a solution, making them pretty uncooperative  in biotech or medical applications.

And on top of all of this, it’s tough to  make them consistent with one another. If some of the onions in a batch aren’t the  same size, or have different numbers of layers, they aren’t all going to have the same properties, which means they might not work together as  well as they would if they were all identical. So over the years, researchers  have experimented with different   carbon sources to see what works best.

In addition to nanodiamonds, they’ve  tried graphite, candle soot, wood, and even tomatoes. But one team may have found the best source yet: the fish scales from black snappers. After a fairly complex cleaning  process to remove unwanted fat, color, and calcium,  they dried them out, and hit them with microwaves!

Now this isn’t quite as simple as throwing  some fish scraps in your microwave at home. They built their own fancy science microwave  to ensure everything was precisely controlled. But they did use the same  frequency that home microwaves use.

Amazingly this makes carbon  nano-onions in just seconds! Weirdly, the researchers don’t exactly  know why fish scales work so well. Their best guess is that molecules of  the protein collagen in the fish scales are really good at absorbing those microwaves,  which makes them heat up super fast.

This triggers a process called pyrolysis,  where organic material breaks down and the carbon atoms rearrange  themselves into a different structure. The nano-onions produced this way  seem to be high quality, consistent, and useful right away. They come pre-equipped  with the functional groups they need.

Given how easily these onions were made, this research could open up a lot  more opportunities for scientists   to explore their practical applications. The team observed that when exposed to  ultraviolet light or an electric current,   these fish scale carbon onions can glow blue,  which led them to build an LED with them.   And because they were such high quality,  those onions were about 10 times better   at producing that light than  nano-onions made other ways. Future research could start a  deeper dive into other applications.

And there may be even more that  scientists haven’t identified yet, since the most significant barrier  to research has been making them. If this new method proves viable, scientists  could have unlocked not just an easier and much more efficient way of creating  nano-onions, but one that’s more sustainable, too. It’s a new kind of recycling!

Technology often takes inspiration from nature, but this is an example of harnessing  a natural manufacturing process, fish growing scales, to aid  our own high tech-ambitions. And if you’re trying to sell a cool new  sustainable technology that you’ve created, Shopify can help you do that. Shopify is an e-commerce platform, which means  they make it easy for you to sell cool stuff.

In fact we are currently using Shopify to sell the SciShow calendars. I built this Shopify site with my colleague, Niki and it was so easy and fun to do. Regardless of what industry you’re in, Shopify has the resources and support  to help you start your business and deepen your relationship with customers.

They have a help center, a blog, and online  courses from successful entrepreneurs. And all of the little things  that you’ll need in your business but might not know how to generate, like pay stubs and barcodes, are  included in Shopify’s toolkit. To take advantage of all of those  resources, and a 14-day free trial, you can head to

Thanks to Shopify for supporting this  video and thank you, to you, for watching! [ ♪ outro ]