The crystal that made room for a CO₂-capturing enzyme

It began with a simple experiment: scientists mixed a known enzyme – the same one that helps us breathe – with a thin, leaf-shaped crystal. Then something extraordinary happened. The crystal quietly changed its shape, carving out tiny cavities – as if making room for the enzyme that would soon begin its CO₂-capturing work.

“It is as if the material is welcoming a friend,” explains Joerg Jinschek, Professor at the National Centre for Nano Fabrication and Characterization, Technical University of Denmark, Kongens Lyngby. “For the first time, we were able to see how a crystal reorganises itself around an enzyme – adapting without losing its order, even though it shouldn’t actually fit. It’s almost as if we had transplanted an organ into the crystal and, as we would for a friend, it adjusts to accommodate it.”

What makes the finding important is the chemistry behind it.

Carbonic anhydrase, the enzyme at the centre of the study, can turn more than a million CO₂ molecules into harmless compounds every second – one of the fastest tricks in biology. A zinc ion in its active site accelerates the reaction far beyond what water alone can achieve.

“On paper it sounds simple – just put the enzyme in a porous material,” Jinschek says. “But the enzyme is far larger than the crystal’s pores, and yet the crystal still grows around it.”

What began as a structural curiosity soon revealed something deeper: a glimpse of how biology and materials might one day merge together. It hints at a new class of materials that do more than capture carbon – they act almost like partners in repairing the planet.

A discovery sparked by a mistake

The most surprising part of the project is how it began. The two young researchers behind the work – Zsófia Bognár and Sara Talebi Deylamani – were never meant to combine their projects.

“Initially we worked on two completely different projects,” says Bognár. “I worked with the carbonic anhydrase enzyme, and Sara worked with the leaf-shaped zeolitic imidazolate frameworks (ZIF-L). We had a workshop where we were supposed to plan how to write up our current results – but instead, we came up with a new idea.”

Talebi Deylamani remembers the time with a laugh. “We kind of misunderstood our task and started to write a research plan to combine our projects,” she says. “We were so enthusiastic that we started the experiments the very next day.”

What looked like a mix-up from the outside quickly became momentum. “In my view, their action was spot on – exactly what we expect from our scientists,” says Jinschek.

Once the idea took shape, neither of the two could let it go. They had stumbled onto a question others had overlooked: what actually happens when a large, fragile enzyme meets a rigid, nanoporous crystal as it grows?

“People tried to immobilise enzymes on very different host materials and to maximise the loading,” says Bognár. “The activity has been tested under extreme conditions, but no one has really looked at the structural details at the nanoscale. Where exactly is the enzyme located in such a crystal? How does it modify the host material? This was not understood until now.”

The misunderstanding opened a space between biology and materials science – a space in which the whole became more than the sum of its parts.

“For us, one plus one equalled three,” says Bognár. “That’s exactly how this collaboration felt.”

Why it matters: nature’s shortcut to capturing carbon

The efficient and sustainable capture of CO₂ is one of the major scientific challenges of this century. Today’s CO₂-capture systems are so energy-intensive that they often erase much of the climate benefit. This is why researchers are now turning to nature’s own blueprints – and few biological tools are as elegant as the enzyme at the centre of this work.

In principle, carbonic anhydrase could also help to capture industrial CO₂ emissions – if it can survive outside the protective environment of a living cell.

However, the use of enzymes in technology is delicate. They unfold when exposed to an unfavourable environment such as heat, pressure or metal ions and quickly lose activity under the changing conditions of industrial processes.

“Enzymes are very sensitive,” explains Zsófia Bognár. “In CO₂ capture technology, there are two columns – an absorber, where we capture the CO₂, and a desorber, where we release it for further use or storage. Temperatures in the desorber exceed 100°C. We have to prevent the enzyme from entering into that column, and one way to do that is to immobilise it.”

A protective host for a fragile enzyme

To protect the enzyme, the team turned to ZIF-L – a metal-organic framework (MOF) and specially developed material that was awarded the Nobel Prize in Chemistry in 2025. Its structure consists of an ultralight scaffold made of zinc and organic linkers, formed into a thin, leaf-shaped crystals filled with tiny, orderly nanocavities.

“I was working with metal-organic frameworks for almost five years,” says Sara Talebi Deylamani. “What’s special about ZIF-L is that it can be synthesised in water at room temperature within a few hours, an environment that enzymes also like. We wanted to avoid damaging the enzyme during the formation of the enzyme–host composite.”

The team’s expectations were modest: embed the enzyme and measure how much activity remained. No one imagined that the host material itself would respond as it did.

“At first, we thought that the enzyme would simply adhere to the surface,” Talebi Deylamani recalls. “None of us expected the host material itself to adapt.”

Even experienced researchers doubted the possibility.

“One would expect the enzyme to attach to the surface or, if embedded, to distort the material – not for the crystal to grow perfectly around it,” says Jinschek.

The turning point: when the crystal starts to adapt

The surprise was not that the enzyme had actually survived synthesis – it was that the MOF crystal adapted to provide room for the enzyme.

The first hints appeared by accident. When Talebi Deylamani examined the enzyme–MOF composite under a scanning electron microscope, the familiar leaf shape of the ZIF-L crystals no longer looked the same.

“The normally smooth edge of the ZIF-L leaf changed into something that more closely resembled a natural leaf with pronounced edges,” says Zsófia Bognár. “That was the first sign – the structure of the materials has changed.”

A spectroscopy measurement strengthened the suspicion: a specific bond in the framework changed.

“We noticed the stretching of a particular chemical bond in Fourier-transform infrared spectroscopy data,” Jinschek recalls. “This was a hint that we needed to take a closer look and zoom in with another technique.”

Yet one of the standard tools for checking crystal structure, X-ray diffraction, showed nothing unusual – it simply cannot detect such small local rearrangements.

Only when the team zoomed in with an advanced electron microscope did the breakthrough become visible: small dark spots – the size of a single enzyme – appeared throughout the crystal, revealing how the rigid material had quietly reorganised itself to make room for the enzyme.

How to visualise it: zooming in to the nanoscale

To understand how a rigid crystal could reorganise itself around an enzyme, the team needed tools powerful enough to see inside the crystal itself. X-ray-based characterization methods cannot detect these small features, but electron-based methods can.

Using a highly sensitive form of electron microscopy, the researchers could map tiny differences inside the thin, leaf-shaped crystals. The adaptation of the structure became unmistakably clear.

“Using electron microscopy, we were able to see the formed nanocavities,” says Joerg Jinschek. “At that moment, we realized that the material had reorganised itself to make space for the enzyme.”

Together, a series of applied methods revealed the complete picture: a rigid inorganic material had remained single crystal while secretly reorganising itself inside and out to host a biological molecule – an arrangement at the nanoscale.

When materials learn to speak biology

What became visible under the electron microscope was more than a structural oddity – it suggested a dialogue between two systems that would normally never interact with each other.

“It really became a balancing act between chemistry and biology,” recalls Sara Talebi Deylamani. “Whenever we changed one thing, something else responded.”

The enzyme wasn’t simply trapped, and the crystal didn’t just serve as a scaffold. Both reacted during growth, shaping each other in subtle and unexpected ways. For Jinschek, this hints at something far beyond carbon capture.

“From our perspective, this is the development of an interface between bio and nano,” he says. “People try to design molecules that carry out the function of enzymes. And here we say: why should we, if nature does the trick? Enzymes are extremely effective – we just help them by attaching them to something inorganic that makes them more stable and transportable.”

His metaphor captures transformation vividly.

“It’s like a transplant – we transfer a specific function into a stable host crystal,” says Jinschek. “We just need to understand how the crystal adapts to the transplant.”

The idea challenges the traditional divide between living and non-living matter. In biology, structure adapts constantly; in inorganic materials, structure dictates function. Seeing a crystal behave with a hint of biological flexibility introduces a new hybrid category – materials that cooperate.

“We believe that the enzyme and the crystal interact during growth – far beyond mere enclosure,” Jinschek notes. “The enzyme shapes the host, and the host in turn shields and supports the enzyme. That reciprocity is what makes this so exciting.”

This raises a deeper question: if a rigid solid can reorganise itself around a molecule of life, what else could future materials do? Could they respond to environmental changes, adapt to stress or self-assemble the way tissues do?

Does it still work? The enzyme survives

Once the crystal had clearly adapted around the enzyme, the next question was unavoidable: had the enzyme survived the process, or had the protective shell become a trap?

A simple colour test provided the answer. The enzyme still turned CO₂ into bicarbonate – clear proof that it remained folded and functioning.

“The enzyme clearly survives the process,” says Zsófia Bognár. “Its reaction rate is somewhat slower, but it remains active – and the crystal protects and stabilises it.”

For industrial use, stability matters more than peak speed – and here the crystal’s adaptation is an advantage.

“We never reached the performance of the free enzyme,” Jinschek explains. “But stabilising it for long-term use is the real benefit.”

The economic angle is equally decisive.

“At the end, everything is about costs,” says Bognár. “If we have to replenish the enzyme frequently, the technology is not sustainable.”

Why efficiency beats packing more in

The discovery that a crystal can adapt around an enzyme is not the end of the story – it’s the beginning. To turn enzyme–host systems into practical CO₂-capture tools, the goal now is not to pack in as many enzymes as possible but to tune the structure for long-term performance.

“The idea that we should optimise rather than maximise immobilisation – that is a really good takeaway,” says Zsófia Bognár.

Traditional approaches try to pack in as much enzyme as possible, even if it distorts the material. Here, the goal is to let enzyme and crystal grow together in a way that keeps both stable and active.

Several directions are already emerging. One approach is to make the ZIF-L crystals thinner.

“CO₂ can diffuse better through a thinner layer of the MOF,” says Talebi Deylamani. “so CO₂ molecules could reach the enzyme more easily.”

Another is to design MOFs with more space around the enzyme or with wider channels – while still using gentle, water-based synthesis that keeps the enzyme intact and fits industrial scale-up.

“If we improve the crystal’s pore structure and increase its surface area, the enzyme will have more space, and CO₂ can move through more easily,” she explains.

Meanwhile, Bognár is pushing toward higher-resolution imaging of the enzyme–MOF interface.

“We are now investigating with high-resolution transmission electron microscopy to really see whether the enzyme also responded – how the two interact,” she says. “Until now, we mostly saw the holes. Now we want to capture the enzyme in the holes.”

Toward materials that help the planet heal

The hybrid crystals developed in this project are small – thin, delicate flakes forming in a beaker of water – but the principles they reveal reach far beyond their size. They suggest a new way to build clean-energy technologies: by letting biology guide the growth and behaviour of solid materials.

“If we can integrate these enzyme–crystal systems into real industrial processes,” says Jinschek, “we could capture carbon from air or exhaust streams far more efficiently and with much less energy input than today’s methods.”

The implications extend well beyond carbonic anhydrase. Many enzymes are more selective and efficient than industrial catalysts – if they can be protected. Materials that adapt around enzymes could unlock new possibilities in biosensing, green chemistry and sustainable manufacturing.

“What excites me the most is that this is not limited to carbonic anhydrase,” says Bognár. “The same approach could work with many other enzymes.”

The leaf-like crystals also echo a deeper metaphor. The researchers often describe the idea of an “artificial leaf” – a human-made material that performs chemical work the way a natural leaf handles CO₂ and light.

It is still far away, but the concept is no longer science fiction. By letting enzymes breathe inside crystals, the researchers have shown that materials do not need to stay static. They can respond. Adapt. Make room for life in a way no one thought possible.

“This is a step toward materials that are not just containers but collaborators,” Jinschek says. “Once a crystal starts to host molecules of life, you see what is possible when nature and technology truly meet.”

One day, such adaptive materials could form the backbone of large-scale carbon-capture systems – restoring part of the planet’s balance not by fighting nature but by finally learning to work with it.