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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.
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