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Atomic Musical Chairs: How Tiny Nanocrystals Are Informing the Future of Energy-Efficient Electronics

Daniel Morton — Tue, 17 Mar 2026 19:43:33 +0000

Atomic Musical Chairs: How Tiny Nanocrystals Are Informing the Future of Energy-Efficient Electronics Daniel Morton Tue, 03/17/2026 - 13:43

Daniel Morton

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While most people, when asked about energy innovation, think about some of the "large" technologies, such as wind turbines, long transmission lines, or massive power plants, some of the most important advances in how we use energy are happening at a scale so small that millions of the "machines" involved could fit on the head of a pin.

New research from a team led by RASEI Fellow Gordana Dukovic, working in collaboration with RASEI Fellow Sadegh Yazdi and Prof. Dmitri Talapin from the University of Chicago, reveals new insights on a high-speed game of "atomic musical chairs." This collaboration involved two large teams working together. Researchers from two United States National Science Foundation Science and Technology Centers (STCs) including IMOD and STROBE, employed cutting-edge microscopy techniques to directly visualize, for the first time at this scale, how atoms swap places inside tiny semiconductor nanocrystals, which is a crucial step toward understanding the composition, and ultimately the properties, of these materials.

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NSF STCc

STROBE STC

IMOD STC

Science and Technology Centers are hubs for collaboration, bringing together multidisciplinary researchers from across the United States to solve large, challenging and complex problems. This article describes a space where two of these large networks worked together. STROBE, or Science and Technology Center on Real-Time Functional Imaging pushes the boundaries of microscopy to observe and understand materials at the atomic and nano-scales. IMOD, or The Center for Integration of Modern Optoelectronic Materials on Demand, focuses on making atomically precise semiconductors and integrating them into applications in VR displays, and devices for quantum communication and computing. This team leverages the expertise from both Centers to create new semiconductors and using cutting-edge microscopes to observe and understand them.

Almost all of our electronic devices are built from semiconductors. Whether it is the screen on your smartphone, the components in your car, or the microchips in your computer, these electronics rely on semiconductors. Traditionally, these materials are "grown" through rigid and often expensive processes. Tuning the properties of a semiconductor using this approach is not straightforward. If you want a specific color of light for a display, or a specific energy absorption profile for a solar panel, you often have to start from scratch with an entirely different material.

This is where semiconductor nanocrystals offer remarkable opportunities. The specific size, shape, and composition of these tiny nanocrystals determine the physical and electronic properties of the overall material. A particularly powerful process with such nanocrystals is called cation exchange. Instead of building a new crystal from scratch, you can take an existing one and swap out its internal atomic components to change its properties.

“This is a project that we have been working on for a long time” explains Ben Hammel, a graduate student in the Dukovic Group, and lead author on this research. “We have been looking at these materials from the Talapin Group for a long time”.

This work, just published in ACS Nano, focuses on what are called III–V nanocrystals, which are tiny, four-sided pyramids, or tetrahedrons, named for the groups of the periodic table their constituent elements come from (Group III includes elements like Indium, Gallium, and Aluminum; Group V includes Phosphorus, Arsenic, and Antimony). In this research, the nanocrystals are made of a mixture of Indium, Phosphorus, and Arsenic. To exert more control over the properties of these nanocrystals, the researchers introduced Gallium. Adding Gallium is like tuning a guitar string: it changes the energy of the crystal, influencing how it interacts with light.

“A lot of people have developed ways to make III-V bulk semiconductors, but the real challenge is making them into nanocrystals, where you have more control over their properties, and the Talapin Group have developed a really neat molten salt process to do this” explains Hammel. The molten salt work was published in Science in 2024.

Imagine the inside of one of these tiny crystals as a perfectly ordered lattice of "seats." There are two types of players: Anions (the Phosphorus and Arsenic atoms) and Cations (the Indium atoms). A key observation from the team was that the "house" never moves. The Anions are like the floor and the chairs, they stay perfectly still, maintaining the overall crystal framework. The Cations, on the other hand, are the players sitting in those chairs.

In this work, the nanocrystals were placed into a "hot bath" of molten Gallium salts, essentially starting the music on the game of atomic musical chairs. Previous work had shown that the atoms exchange, but there was not a lot of evidence for how this process worked. “Understanding how this works is very important, and finding out more about the local elemental composition, and how the Gallium atoms move can inform how we design these systems in the future” explains Hammel.

These nanocrystals are only 5 to 10 nanometers wide. A typical human hair is between 80,000 and 100,000 nanometers wide. These crystals are called "nano" for a reason! To observe this game of atomic musical chairs in action, the team used Scanning Transmission Electron Microscopy (STEM), an instrument that uses a focused beam of electrons to probe and image matter at the atomic scale. “Early on there were some signs that there was heterogeneity within the particles, but it was unclear, a big technical challenge we had to overcome was how we can actually measure the Gallium moving through the nanocrystal” said Hammel.

A key challenge they had to figure out was the sensitivity of the nanocrystals to the very tool being used to study them. The electron beam of the STEM, if used at high intensity, can damage the nanocrystals before a useful image can even be collected. To solve this, the team developed an innovative "statistical" imaging approach. Rather than blasting a single crystal with a high dose of electrons to get a sharp image, the researchers instead took many low-dose, and individually blurry, snapshots of hundreds of different crystals at different stages of the molten salt reaction. “We essentially stacked the data on top of each other” describes Hammel, “If I can add together 10 nanocrystals, I can get 10 times the signal”. Adding these kinds of signals together hadn’t been done before with semiconductor nanocrystals. “A lot of this came together from teamwork, I got a lot of really great suggestions from collaborators on how to collect and analyze this information. I used a suite of open source Python tools, which I was a little lost with until I met the researcher who developed them at a conference (Josh Taillon from NIST), who gave me some great suggestions and ideas” said Hammel. Using these advanced computer algorithms, they aligned and stacked hundreds of images on top of each other. Much like a long-exposure photograph of the night sky reveals stars the naked eye cannot see, this averaged stacked image revealed a detailed map of where the Gallium atoms were moving inside the nanocrystals. To the team’s knowledge, this signal-averaging approach for elemental mapping has not previously been applied to semiconductor nanocrystals.

The Gallium atoms rush in to claim “seats”, but not randomly. Gallium grabs the seats near the surface first. Because of the high surface-to-volume ratio of these tiny particles, this surface exchange causes a dramatic and rapid change in overall composition: within the first 15 minutes in the molten salt bath, the outside of the nanocrystals is substantially transformed. However, as the game goes on, it gets progressively harder. The Indium atoms sitting in the seats at the center of the nanocrystal are crowded in, and for a Gallium atom to reach the core, an Indium atom must fight its way out through an increasingly Gallium-rich lattice. This sets up a compositional gradient, essentially a smooth transition from a Gallium-rich exterior to an Indium-rich core, that persists even after 16 hours of reaction.

This new methodology, combining STEM with advanced computational image processing, is sensitive enough to detect and map the movement of atoms through individual nanocrystals. Applying it here directly revealed that the cation exchange process (Indium being replaced by Gallium) creates a graded composition rather than a simple sharp boundary between materials. The team also used computer simulations (finite element analysis in COMSOL) to model this exchange as a diffusion-limited process, finding that the rate of exchange slows dramatically as more Gallium enters the lattice, likely because the smaller Gallium atoms cause the lattice to contract, making it progressively harder for further exchange to occur.

Importantly, the methods developed in this work are broadly applicable and could be used to determine the elemental composition of many other types of nanocrystals that have previously been difficult to study due to their sensitivity to electron beams.

The ability to observe and better understand the cation exchange process in these semiconductor nanocrystals has significant implications for the development of next-generation materials. It has been suggested that graded compositions, like those observed here, could help suppress certain energy-loss processes in semiconductor devices, potentially enabling more efficient lighting and lower-power electronics. Whether these specific nanocrystals deliver on that promise remains an open and exciting research question, but this work provides the observational foundation needed to begin answering it. Additionally, the molten-salt synthesis approach that underpins this research is an active area of development as a potentially more versatile route to III–V semiconductor nanocrystals, materials that have historically been among the most challenging to synthesize with fine compositional control.

By developing new tools to better observe the game of "atomic musical chairs," the researchers are providing the field with insights into how to engineer materials at the atomic scale and revealing that the path from one material to another is more nuanced, and more interesting, than previously understood.

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2026 Three Minute Thesis Finalists

Daniel Morton — Tue, 24 Feb 2026 20:57:33 +0000

2026 Three Minute Thesis Finalists Daniel Morton Tue, 02/24/2026 - 13:57

Daniel Morton

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��Ҵ�ý�ƽ�� 3MT Competition

2026 3MT Announcement

Recording of 2026 3MT Final

Meet 3MT Finalist Ben Hammel

Ben Hammel, a graduate student in the Dukovic Group, was a finalist in the 2026 ��Ҵ�ý�ƽ�� Three Minute Thesis Competition. We caught up with Ben to find out more about the whole 3MT process.

What is 3MT?

3MT stands for Three-Minute Thesis, which was a competition started at the University of Queensland. I think the history behind it is that they were going through droughts in Australia and everyone had these three-minute egg timers in their showers to limit water usage. Someone had this idea of maybe this was a good challenge for condensing/communicating your research: how well can you present your thesis in three minutes?

What did you have to do?

I came into this wanting to learn how to clearly describe my research. The rubric is really about explaining your science. They look at clarity, your enthusiasm, and about the slide and presentation. But they also look at can you describe the motivation of your research? Can you describe the design of your research? Can you describe the conclusions and societal impact of your work? So it is about science communication, with a strong grounding in the scientific aspects. Going through this process and thinking through these things has given me a better understanding of my own science.

Can you describe your research in five words?

Using microscope to look at nanocrystals. Six, that is ok, right?

What drew you to do the 3MT?

I wanted to improve my scientific communication skills, and I felt like there was something really cool about my research that I wanted to share. It is this simple idea that we need to look at nanocrystals to understand how they work. I get to use this amazing microscope to do just that!

What was the best part of the 3MT program?

The best part was definitely the cohort of talks. In the final competition folks got to see eleven presentations from across the graduate school, and that was awesome, but in the preliminary round there were more than 25. There were so many great talks from so many parts of the school that I got to see. It was really fun. You get to see in an hour so much condensed scientific knowledge. That was definitely the best part.

What was the worst/hardest part of the 3MT program?

The hardest part was talking about the science. It is so easy for me to say “we study these nanocrystals, and they’re cool, and I use this microscope”, but when people really ask me about what are the scientific questions you have and what are the experiments you run to answer them? And how are you going to engineer nanocrystals? It’s difficult to answer these kinds of technical questions in an accessible way.

How do you think your experience in 3MT will help you in the future?

Oh, it’s already helping me! Just in the way I talk to people and explain things. I feel like it has made me intellectually stronger and I am already noticing that it helps me communicate more clearly and think about my research in different ways.

What would you say to a grad student considering doing 3MT in the future?

Strongly recommend. It will take up a decent amount of your time, but it is definitely worth it. Don’t be afraid to tackle hard scientific concepts! One thing I regret not doing more of is really trying hard to tackle quantum mechanics in my talk. The properties of quantum dots are derived from quantum mechanics and I was scared to try to explain that, and I made my explanation totally classical. I was describing electricity flowing through crystals, but I think that people were hungry to learn more about the deeper science, and I should have given it a shot, at least to practice it and see if I could do it.

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RASEI Fellow Gregor Henze selected as 2026 ASHRAE Fellow

Daniel Morton — Wed, 11 Feb 2026 18:32:48 +0000

RASEI Fellow Gregor Henze selected as 2026 ASHRAE Fellow Daniel Morton Wed, 02/11/2026 - 11:32

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ASHRAE

ASHRAE 2026 Press Release

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers, or ASHRAE, is dedicated to advancing human well-being through sustainable technology for the built environment. Founding in 1959 through the merger of professional societies dating back to 1894, ASHRAE members focus on building systems, energy efficiency, indoor air quality, refrigeration and sustainability within the industry.

Each year ASHRAE recognizes and celebrates the contributions of its outstanding members, highlighting their work and significant contributions to the field. This year RASEI Fellow Gregor Henze was selected to the 2026 cohort of 24 ASHRAE Fellows. The status of Fellow recognizes members who have attained distinction and made substantial contributions such as education, engineering design and consultation, publications, presentations and mentoring.

Congratulations Gregor!

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RASEI Fellow Jeff York on the next chapter for Colorado Craft Beers

Daniel Morton — Tue, 10 Feb 2026 19:39:28 +0000

RASEI Fellow Jeff York on the next chapter for Colorado Craft Beers Daniel Morton Tue, 02/10/2026 - 12:39

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How one engineering alum optimizes clean energy operations before they break

Daniel Morton — Thu, 05 Feb 2026 16:21:18 +0000

How one engineering alum optimizes clean energy operations before they break Daniel Morton Thu, 02/05/2026 - 09:21

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RASEI Fellow Kat Knauer selected as a 2026 Gilbreth Lecturer

Daniel Morton — Wed, 28 Jan 2026 16:36:05 +0000

RASEI Fellow Kat Knauer selected as a 2026 Gilbreth Lecturer Daniel Morton Wed, 01/28/2026 - 09:36

Daniel Morton

The Gilbreth Lectures recognize early-career engineers and provides a platform to share their work broadly with the National Academy of Engineering (NAE) Community.

The Gilbreth lectures were established in 2001 by the Council of the National Academy of Engineering as a means of recognizing outstanding young American engineers and making them more visible to NAE members. Recipients of the lectureships are nominated from The Grainger Foundation Frontiers of Engineering program and are given the opportunity to make presentations at the NAE’s fall Annual Meetings and spring National Meetings.

The Gilbreth Lectureships are named in honor of Lillian Gilbreth, the first woman elected to the National Academy of Engineering in 1965. Lillian was a pioneer in the field of Human Factors, often considered to be the first industrial/organizational psychologist, whose research helped industrial engineers recognize the importance of the psychological dimensions of work.

Kat’s selection was based on her talk at the U.S. Frontiers of Engineering symposium on “AI-Driven Plastic Redesign for Recyclable Materials”. Congratulations to Kat, and we look forward to hearing about the presentations!

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The case of the vanishing seeds: How curiosity-driven research is future-proofing “Smart Windows”

Daniel Morton — Tue, 27 Jan 2026 17:02:14 +0000

The case of the vanishing seeds: How curiosity-driven research is future-proofing “Smart Windows” Daniel Morton Tue, 01/27/2026 - 10:02

Daniel Morton

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Have you ever walked into a room on a glorious Colorado summer day and felt the heat radiating through the glass?

We usually solve this by cranking up the air conditioning or closing the blinds, losing our mountain view in the process. But what if the window itself could think? A team led by Mike McGehee, a Fellow at RASEI, describes research that improves the robustness of such a device.

For years researchers have been working on “smart windows”, devices that could “sense” the conditions outside and “react” to them. This investigation centers around a promising technology called Reversible Metal Electrodeposition (RME). The technical details of this process are complex, but you can understand the concept by thinking of it as a reversible coat of paint. At the flip of a switch, a thin layer of metal, in this case silver, spreads across the glass to form a layer that tints it, blocking out the heat and the glare. Flip the switch again and the silver dissolves back into a clear liquid, making the window transparent.

Buildings are responsible for consuming around 40% of all generated energy globally, much of which is expended in regulating the temperature, heating and cooling the building interior. Installing smart windows that can react to the environmental conditions could provide a very effective mechanism to reduce energy use and slash energy bills by automatically managing how much heat enters a room. It has been estimated that just by controlling the amount of sunlight that is let into a building through a window, we could cut energy bills by up to as much as 20%.

However, there have been a number of challenges to overcome in order to take this initial discovery from the lab to a product that can be deployed for use in buildings. One challenge is that early versions of these windows started out fast but grew “lazy” over time. After a few thousand uses the tinting / de-tinting process slowed, taking almost four times longer than it did on day one.

This is where the researchers undertook some detailed investigations to identify what was going on, and what could be done to fix it. A collaboration between the McGehee group (at the University of Colorado Boulder) and the Barile Group (at the University of Nevada) set out to find out exactly what was happening. The team decided to look closer, using a combination of high-powered x-rays and electrochemical tests. The windows were using tiny “seeds” of platinum to help the silver grow on the glass. Platinum is recognized for being tough and non-reactive, and so should be perfect as a nucleation point for the silver. Using these advanced techniques the team explored exactly what was happening to the platinum seeds during the clearing phase, when the silver “paint” is stripped away.

To their surprise, the platinum was not as tough as they initially thought. In the special liquid environment needed for the windows, the platinum seeds were actually dissolving and washing away when the window was switched to clear. As the number of seeds dropped, the silver had fewer locations to grow from, which was the cause behind the window tinting slowing.

This led the team to ask the question “What can we do to make the seeds more resilient?”, which led them to use gold in place of platinum. While gold and platinum are both precious metals, in water, which is the solvent used inside the window panels, gold is more stable and less susceptible to decomposition and dissolving. When they swapped the platinum seeds for gold ones, the results were immediate. Even after 7,500 cycles, the equivalent of years of daily use, the windows transitioned just as fast as the first time they were used.

These gold-based windows provide an exciting range of opportunities. Not only because of their improved stability over many thousands of cycles, but also because they can express multiple colors by varying the voltage, a feature of the size of the gold particles. This presents opportunities for their use in displays and communications devices. This technology offers a better, smarter window that could passively save significant amounts of energy if deployed in commercial and residential buildings. This work shows how the impact of making fundamental chemical changes can unlock the potential of new technologies.

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Push for Nuclear Energy in Colorado

Daniel Morton — Wed, 21 Jan 2026 23:48:05 +0000

Push for Nuclear Energy in Colorado Daniel Morton Wed, 01/21/2026 - 16:48

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Locking in Solar Power: How a Stronger Interlayer Boosts Perovskite Cell Durability

Daniel Morton — Mon, 05 Jan 2026 19:31:00 +0000

Locking in Solar Power: How a Stronger Interlayer Boosts Perovskite Cell Durability Daniel Morton Mon, 01/05/2026 - 12:31

New Molecular Designs Extend the Life and Efficiency of Next-Generation Solar Cells

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Posted on the RASEI website with permission and minor modifications from the piece published by David DeFusco on the UNC Chapel Hill Applied Physical Sciences Site here.

A new study published in Science led by researchers at UNC-Chapel Hill, with collaborators from the Renewable and Sustainable Energy Institute (RASEI), explains why perovskite solar cells—fast-rising rivals to traditional silicon panels—tend to break down under prolonged heat and sunlight, especially ultraviolet light, and reveals a promising strategy to dramatically slow that damage.

The work focuses on a thin “interlayer” that sits between the electrode and the perovskite material inside a solar cell. This layer is only a single molecule thick, but it plays an outsized role in how long the device lasts.

“These interlayers are meant to help charges move efficiently out of the perovskite and into the circuit,” said Chengbin Fei, first author of the study and a postdoctoral researcher in UNC’s Department of Applied Physical Sciences. “But we found that some of the same chemical features that make them useful can also cause long-term damage if they’re not tightly attached to the electrode.”

Many high-performance perovskite solar cells use interlayers based on phosphonic acids. These molecules stick to a transparent electrode made of indium tin oxide, or ITO, and help pull positive charges out of the perovskite. Until now, most researchers assumed these layers were harmless once installed. Fei and his colleagues discovered that this is not always true.

The researchers found that some of these tiny helper molecules aren’t firmly stuck to the solar cell’s surface. When the cell gets hot or sits in sunlight that includes ultraviolet rays, those that are loosely attached molecules can break free. Once that happens, they start interfering with the solar material itself. They trigger harmful changes inside the cell: key ingredients fall apart, iodine-related components react in damaging ways and lead turns into a form that no longer works properly. Over time, all of this damage adds up and causes the solar cell to produce less and less electricity.

“In simple terms, the acid part of these molecules can act like a slow poison,” said Fei. “At high temperatures and under UV light, it accelerates chemical reactions that the perovskite just can’t tolerate.”

To understand what was happening, the researchers used a range of techniques, including spectroscopy and X-ray measurements, to watch how the materials changed over time. They found that stronger acids caused faster damage and that UV light made the reactions much worse. This explained why devices that look stable at first can fail after hundreds or thousands of hours outdoors.

The key advance came when the researchers at UNC and the University of Colorado Boulder created a new version of this thin helper layer containing a combination of two molecules that sticks much more tightly to the electrode surface. Seth Marder, the senior author at the University of Colorado-Boulder and Director of the Renewable and Sustainable Energy Institute (RASEI) says “the molecule our team developed was designed to not only interact with the electrode surface but more strongly with its neighboring molecules. Consequently the molecules stay more securely in place, reducing the reactive parts that can break away and damage the solar material that is deposited on top ”. As a result, the layer still helps charges flow out of the cell, but it no longer triggers the damaging reactions that shorten the cell’s lifetime.

Simply put, “when the molecule is firmly locked onto the surface, it can’t wander into the perovskite and cause trouble,” said Fei. “That simple change makes a huge difference over time.”

Solar cells made with the new interlayer design showed striking improvements and met a key performance milestone. Under harsh test conditions—85 degrees Celsius, continuous bright light that included UV and constant operation—the devices ran for nearly 3,000 hours before losing just 10 percent of their efficiency. That level of durability has not been reported before for this type of perovskite solar cell.

The molecule our team developed was designed to not only interact with the electrode surface but more strongly with its neighboring molecules. Consequently the molecules stay more securely in place, reducing the reactive parts that can break away and damage the solar material that is deposited on top.
- Seth Marder

The researchers also scaled up their approach to small solar modules, closer to what might be used in real products. These “minimodules,” about the size of a postcard, reached power conversion efficiencies above 22 percent and kept working for more than 2,000 hours under the same stressful conditions, which is considered very high performance for this type of solar technology.

Jinsong Huang, senior author of the paper and UNC Louis D. Rubin Distinguished Professor, said the results address one of the most important barriers to commercialization. “Efficiency alone is not enough,” he said. “For perovskite solar technology to succeed outside the lab, it must survive heat, light and time. This work shows a clear chemical pathway to make that happen.”

Beyond improving one specific material, the study sends a broader message to the field. Tiny details at buried interfaces—places that are hard to see and easy to overlook—can control the lifetime of an entire solar module. By understanding and managing these details, researchers can design devices that last far longer.

“This study reminds us that stability is a chemistry problem as much as an engineering one,” said Wei You, a co-author of the study and UNC Cary C. Boshamer Distinguished Professor of Chemistry and Applied Physical Sciences. “Once you understand the chemistry, you can start to fix it.”

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The Filament Factory: How two specialized cells team up to build microscopic rock and drive carbon capture

Daniel Morton — Mon, 05 Jan 2026 17:26:55 +0000

The Filament Factory: How two specialized cells team up to build microscopic rock and drive carbon capture Daniel Morton Mon, 01/05/2026 - 10:26

Daniel Morton

In the tiny, beaded chain of the cyanobacterium Anabaena sp. ATCC 33047, two different cells, the photosynthetic factory worker and the nitrogen-fixing specialist, play distinct and powerful roles in creating solid minerals.

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A team led by Renewable And Sustainable Energy Institute (RASEI) Fellow Jeff Cameron and Nature, Environment, Science & Technology (NEST) Studio co-founder Erin Espelie, used advanced high-resolution microscopy to capture the key moments; the factory worker leaks materials when stressed, and the specialist accelerates crystal growth through contact, proving that single-cell behaviors are a vital trigger for biomineralization. Understanding the cellular processes could inform large-scale applications, from oceanic buffering and soil improvement to mineral formation, and living building materials that sequester carbon.

A central enabling technology to lower pollution and reduce carbon emissions is developing clever ways to capture, and handle carbon dioxide. One avenue of investigation is to use processes already developed by Nature. There is significant research focused on using one of the Earth’s oldest and powerful processes: Microbiologically Induced Calcium Carbonate Precipitation, or MICP for short. Bacteria and algae through their normal life functions naturally create rock, specifically calcium carbonate, the main component of limestone. This process is a critical process in oceanic buffering and holds immense potential promise for green technologies. If we can understand, and harness this process, we could use such bacteria for a broad range of applications. We could create “living” cements for self-healing concrete, stabilize fragile soils, even enhance industrial carbon dioxide sequestration. However, to control this process we first need to understand the specific cellular blueprints that guide these microbial construction projects. Until now, those blueprints have been frustratingly fuzzy.

To better understand the puzzle of biomineralization the team explored the cellular structure of the cyanobacteria Anabaena sp. ATCC 33047 (hereafter Anabaena). Think of this organism as a tiny “Filament Factory”, one that grows as a string of cells, essentially a beaded green chain (they show up as red in the images because of the microscopy technique), where labor is divided in specific jobs. The links in the chain are not identical, it contains two specialized cell types that perform distinct, but equally important tasks.

First, let’s consider the Vegetative Cells, which are like tireless “Photosynthetic Factory Workers”. These are the green, abundant cells with the primary job of harvesting solar energy to convert carbon dioxide into sugars (Photosynthesis). This process has long been proposed as the main cause for triggering rock formation through MICP, as it raises the local pH, making the environment more alkaline, which encourages calcium carbonate to precipitate.

The other kind of cells, which can be found scattered along the filament, are called Heterocysts. These are like “Nitrogen-Fixing Specialists”. These cells are slightly larger, more solidly built, and specialize in converting atmospheric nitrogen gas into a usable form for the entire filament. This requires an extremely lo-oxygen environment, distinguishing the heterocysts and giving them a significant influence over the cells surrounding chemical environment.

To understand the process in a stepwise fashion the team were able to treat the bacterial system with a specific nutrient cocktail that essentially “turned off” the generalized photosynthesis-driven precipitation and instead focus solely on the effects of these two specialized cells. By developing approaches to shutdown specific parts of the process the team could use advanced microscopy techniques to better pin-point the single-cell behaviors responsible for triggering the formation and growth of microscopic rock.

Unlocking this level of detail in the cellular workings of a cyanobacteria requires specialized tools. The researchers used a suites of powerful high-resolution techniques to interrogate the bacteria, including Quantitative Fluorescence Microscopy and Raman Microscopy, that enabled them to watch the action unfold. The ability to directly observe the single-cell processes was critical to determining how the “Filament Factory” uses two distinct mechanisms for biomineralization.

The first observation centers around the Vegetative Cells, or the “Photosynthetic Factory Workers”. While the cells are usually busy using solar energy to capture carbon dioxide the high-resolution microscopy captured what happens when these cells are under mechanical stress, such as when they are bent by other cells, or squashed against an existing mineral structure. The team were able to watch in real-time as this physical pressure caused the cells membrane to rupture. This breach of the membrane releases, or leaks, a key chemical, the sequestered inorganic carbon (bicarbonate) that the cell was holding inside. This rapid, localized surge of carbon creates excellent conditions for the formation of a new crystal at the leakage site. This reframes the start of the process. It is not just a passive gradual change in the environment that causes crystal growth, instead it can be caused by an active, stress-induced cell failure that is a trigger for calcite crystal nucleation.

The second observation concerns the actions of the Heterocyst Cells, or the “Nitrogen-Fixing Specialists”. Using the powerful techniques that enabled the researchers to peer into the inner workings of the cells the team were able to confirm that when a heterocyst cell came into direct contact with an existing calcite crystal “seed”, the crystal experienced rapid and dramatic growth. Crucially, this accelerated growth did not happen when a vegetative cell touched the crystal.

The team proposes that this dramatic crystal growth is connected to the function of Heterocyst Cell. Nitrogen fixation is a chemical transformation that consumes protons (H⁺). By pulling these protons out of the surrounding water, the heterocyst locally, and rapidly, increases the pH (alkalinity) of the microenvironment, which is amplified at the point of contact. This sudden shift in pH provides ideal conditions to effectively “glue” dissolved ions onto the existing crystal, resulting in rapid growth.

These findings describe how these two specialized cells have complementary roles. One is the nucleation trigger when stressed, and the other is the growth accelerator when in contact.

This detailed observation and analysis of the processes happening at the single-cell level shifts our understanding around the processes involved in biomineralization. Instead of thinking of microbial rock formation as a slow and uniform chemical reaction driven by large-scale phenomena like photosynthesis, this work illustrates mechanisms that are controlled and function-specific processes that are dictated by the precise cellular roles and localized behavior of individual cells.

The understanding building from these findings has the potential to inform a wide-range of applications. By isolating the “stress leak” trigger in vegetative cells and the growth accelerator from the heterocysts, researchers could design systems that intentionally apply mechanical stress, triggering crystal formation and accelerating the growth of carbon dioxide sequestering materials. This could have application in oceanic buffering and technologies for bio-concrete and soil rectification.

The development and application of advanced microscopic techniques has provided the bio-engineering world a new set of variable that they can use in bacterial engineering. By moving from a vague knowledge of “microbes make rock”, to a precise understanding of how the “Filament Factory” uses specialized cells to build, and grow, calcite crystals, the field is a step closer to harnessing this powerful natural approach for using carbon dioxide in a cleaner, more efficient way.

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