Caterpillar Guts: Key to Nanomaterials Production?

Making new nanomaterials could be as easy as giving caterpillars nanocarbon belts to nibble on and then processing their poo, RIKEN chemists have discovered¹. This surprising discovery could pave the way for totally new chemical synthesis methods in the lab.

When he started out as a researcher, Kenichiro Itami never envisioned that one day he would be scraping up and using caterpillar droppings. That's because he's not a biologist, but a chemist specializing in minuscule rings and carbon nanobelts. But innovative research often involves thinking outside the box.

The team at the RIKEN Molecule Creation Laboratory is studying the building blocks of carbon nanotubes, which are nanometer-scale cylinders of carbon atoms that can be used to create light-weight materials notable for their strength and electrical conductivity.

Itami's team usually synthesizes these carbon 'nanobelt' and 'nano-ring' components in a pristine chemistry lab using high-purity chemicals and squeaky-clean flasks. For example, they recently used conventional chemistry to add sulfur-containing functional groups to carbon nanobelts to create strong and light nanomaterials with useful semiconducting and fluorescence properties (see page 15)².

Unconventional plan

But one day, inspired by conversations on so-called 'xenobiotic metabolism' with some of his team members who have a background in biology, Itami had an outlandish idea-what would happen if he used insects to synthesize chemicals? Rather than trying to make new forms of carbon nanobelts via more traditional lab-based methods, could he feed carbon nanobelts to caterpillars and then look at what comes out of the other end?

Xenobiotic metabolism is a process whereby living organisms modify foreign chemicals, such as drugs or pollutants, to make them more water soluble for excretion. "For organic chemists like us, using insects for chemical synthesis was an unbelievably crazy idea," Itami admits.

The results were very disappointing the first time his team tested their idea: they ended up with a lot of dead caterpillars. They had fed silkworms a diet of boiled kidney beans and agar laced with carbon nano-rings, but the nano-rings turned out to be toxic to the caterpillars.

The team then decided to try a hardier species of caterpillar, the tobacco cutworm (or cotton leafworm). These larvae turn into large moths with a voracious appetite that are a pest across Asia and Oceania, damaging economically important crops. Moreover, they are reported to possess roughly twice as many detoxifying enzymes as domestic silkworms.

'Totally unexpected'

This time most of the caterpillars survived - and the team got a shock after two days when they collected the droppings and extracted and purified the chemicals within them. X-ray diffraction revealed that the caterpillars had slipped an oxygen atom into many of the carbon nanobelts. The researchers were able to deduce by increases in metabolism-related gene expression that a group of gut enzymes that modifies chemicals for excretion was responsible. They confirmed their finding by grafting the gene for these enzymes into Escherichia coli bacteria and then observing the same reaction with the carbon nanobelt.

Strikingly, the reaction that inserted the oxygen atom involved breaking a highly stable carbon-carbon bond, which usually requires a lot of energy. It would be challenging to make the same chemical in a lab using conventional methods, says Itami.

"That was totally unexpected," he recalls. "When we saw this result, we were like 'wow!' and the lab was full of excitement."

Although the resulting oxygen-containing carbon nanobelt currently lacks known industrial applications, the experiment highlights the promise of insects as novel tools for chemical synthesis. "We've demonstrated the potential of 'in-insect' synthesis for producing entirely new molecules," Itami says.

The tobacco cutworms also produced the compound in much higher quantities than the team had expected.

"We initially had isolated yields of about 1%, which was already a lot, because we didn't expect high-yielding reactions within an insect. But later we got close to yields of 10% by optimizing feeding concentrations and the purification process," says Itami, who notes that the yields could potentially be improved further.

Zero to hero

The team used carbon nanorings made up of six benzene rings in their initial experiments. But when they repeated the experiment with rings with five, seven, eight, nine, ten, eleven or even twelve benzene rings, nothing happened. Itami suspects this is because enzyme activity is highly selective, and dependent on very specific chemical structures.

There was an element of serendipity involved in the discovery, as the team had never attempted anything like this before, Itami notes.

"In retrospect, we were pretty lucky to be able to discover this reaction, because we just happened to start with the one carbon nanoring that works with tobacco cutworms," he says. "If we'd started with one of the other nano-rings, we wouldn't have seen any reaction and might have given up."

The team is now experimenting to see if they can use different types of insects besides caterpillars to synthesize chemicals. "Other researchers become extremely excited when I present this work at conferences, and tend to ask 'what about using cockroaches or grasshoppers?'," Itami says. "That's something we're looking into now."

For Itami, one of the most appealing aspects of the discovery was that a notorious pest can have uses in the lab. "Tobacco cutworms are a serious pest that everybody wants to eliminate," he says. "But while they are the bad guys for others, they became the heroes in our study."

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References

• 1. Usami, A., Kono, H., Austen, V., Phung, Q. M., Shudo, H. et al. In-insect synthesis of oxygen-doped molecular nanocarbons. Science 388, 1055-1061 (2025). doi: 10.1126/science.adp9384
• 2. Shudo, H., Wiesener, P., Kolodzeiski, E., Mizukami, K., Imoto, D. et al. Thiophene-fused aromatic belts. Nature Communications 16, 1074 (2025). doi: 10.1038/s41467-025-55896-w

About the researcher

Kenichiro Itami