New atomic sensors could lead to a new generation of smart materials

At left, natural diamonds glow under ultraviolet light owing to their various nitrogen-vacancy (NV) centers. At right, a schematic depicting the diamond anvils in action, with NV centers in the bottom anvil. The NV sensors glow a brilliant shade of red when excited with laser light. By probing the brightness of this fluorescence, the researchers were able to see how the sensors responded to small changes in their environment. (Credits: Norman Yao/Berkeley Lab; Ella Marushchenko)

Scientists at Berkeley Lab, UC Berkeley convert diamonds’ atomic flaws into atomic sensors with front-row seats to a quantum world of materials under extreme pressure

Since their invention more than 60 years ago, diamond anvil cells have made it possible for scientists to recreate extreme phenomena – such as the crushing pressures deep inside the Earth’s mantle – or to enable chemical reactions that can only be triggered by intense pressure, all within the confines of a laboratory apparatus that you can safely hold in the palm of your hand.

To develop new, high-performance materials, scientists need to understand how useful properties, such as magnetism and strength, change under such harsh conditions. But often, measuring these properties with enough sensitivity requires a sensor that can withstand the crushing forces inside a diamond anvil cell.

Since 2018, scientists at the Center for Novel Pathways to Quantum Coherence in Materials (NPQC), an Energy Frontier Research Center led by the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), have sought to understand how the properties of electronic and optical materials can be harnessed to develop ultrasensitive sensors capable of measuring electric and magnetic fields.

Now, a team of scientists led by Berkeley Lab and UC Berkeley, with support from the NPQC, have come up with a clever solution: By turning natural atomic flaws inside the diamond anvils into tiny quantum sensors, the scientists have developed a tool that opens the door to a wide range of experiments inaccessible to conventional sensors. Their findings, which were reported today in the journal Science, have implications for a new generation of smart, designer materials, as well as the synthesis of new chemical compounds, atomically fine-tuned by pressure.

Turning atomic flaws into sensors

At the atomic level, diamonds owe their sturdiness to carbon atoms bound together in a tetrahedral crystal structure. But when diamonds form, some carbon atoms can get bumped out of their “lattice site,” a space in the crystal structure that is like their assigned parking spot. When a nitrogen atom impurity trapped in the crystal sits adjacent to an empty site, a special atomic defect forms: a nitrogen-vacancy (NV) center.

Over the last decade, scientists have used NV centers as tiny sensors to measure the magnetism of a single protein, the electric field from a single electron, and the temperature inside a living cell, explained Norman Yao, faculty scientist in Berkeley Lab’s Materials Sciences Division and assistant professor of physics at UC Berkeley.

To take advantage of the NV centers’ intrinsic sensing properties, Yao and colleagues engineered a thin layer of them directly inside the diamond anvil in order to take a snapshot of the physics within the high-pressure chamber.

Imaging stress inside the diamond anvil cell

After generating a layer of NV center sensors a few hundred atoms in thickness inside one-tenth-carat diamonds, the researchers tested the NV sensors’ ability to measure the diamond anvil cell’s high-pressure chamber.

The sensors glow a brilliant shade of red when excited with laser light; by probing the brightness of this fluorescence, the researchers were able to see how the sensors responded to small changes in their environment.

What they found surprised them: The NV sensors suggested that the once-flat surface of the diamond anvil began to curve in the center under pressure.

Co-author Raymond Jeanloz, professor of earth and planetary science at UC Berkeley, and his team identified the phenomenon as “cupping” – a concentration of the pressure toward the center of the anvil tips.

“They had known about this effect for decades but were accustomed to seeing it at 20 times the pressure, where you can see the curvature by eye,” Yao said. “Remarkably, our diamond anvil sensor was able to detect this tiny curvature at even the lowest pressures.”

There were other surprises, too. When a methanol/ethanol mixture they squeezed underwent a glass transition from a liquid to a solid, the diamond surface turned from a smooth bowl to a jagged, textured surface. Mechanical simulations performed by co-author Valery Levitas of Iowa State University and Ames Laboratory confirmed the result.

“This is a fundamentally new way to measure phase transitions in materials at high pressure, and we hope this can complement conventional methods that utilize powerful X-ray radiation from a synchrotron source,” said lead author Satcher Hsieh, a doctoral researcher in Berkeley Lab’s Materials Sciences Division and in the Yao Group at UC Berkeley.

Co-lead authors with Hsieh are graduate student researcher Prabudhya Bhattacharyya and postdoctoral researcher Chong Zu of the Yao Group at UC Berkeley.

Magnetism under pressure

In another experiment, the researchers used their array of NV sensors to capture a magnetic “snapshot” of iron and gadolinium.

Iron and gadolinium are magnetic metals. Scientists have long known that compressing iron and gadolinium can alter them from a magnetic phase to a nonmagnetic phase, an outcome of what scientists call a “pressure-induced phase transition.” In the case of iron, the researchers directly imaged this transition by measuring the depletion of the magnetic field generated by a micron-size (or one millionth of a meter) bead of iron inside the high-pressure chamber.

In the case of gadolinium, the researchers took a different approach. In particular, the electrons inside gadolinium “happily whiz around in random directions,” and this chaotic “mosh pit” of electrons generates a fluctuating magnetic field that the NV sensor can measure, Hsieh said.

The researchers noted that the NV center sensors can flip into different magnetic quantum states in the presence of magnetic fluctuations, much like how a compass needle spins in different directions when you wave a bar magnet near it.

So they postulated that by timing how long it took for the NV centers to flip from one magnetic state to another, they could characterize the gadolinium’s magnetic phase by measuring the magnetic “noise” emanating from the gadolinium electrons’ motion.

They found that when gadolinium is in a non-magnetic phase, its electrons are subdued, and its magnetic field fluctuations hence are weak. Subsequently, the NV sensors stay in a single magnetic quantum state for a long while – nearly a hundred microseconds.

Conversely, when the gadolinium sample changed to a magnetic phase, the electrons moved around rapidly, causing the nearby NV sensor to swiftly flip to another magnetic quantum state.

This sudden change provided clear evidence that gadolinium had entered a different magnetic phase, Hsieh said, adding that their technique allowed them to pinpoint magnetic properties across the sample with submicron precision as opposed to averaging over the entire high-pressure chamber as in previous studies.

The researchers hope that this “noise spectroscopy” technique will provide scientists with a new tool for exploring phases of magnetic matter that can be used as the foundation for smaller, faster, and cheaper ways of storing and processing data through next-generation ultrafast spintronic devices.

Next steps

Now that they’ve demonstrated how to engineer NV centers into diamond anvil cells, the researchers plan to use their device to explore the magnetic behavior of superconducting hydrides – materials that conduct electricity without loss near room temperature at high pressure, which could revolutionize how energy is stored and transferred.

And they would also like to explore science outside of physics. “What’s most exciting to me is that this tool can help so many different scientific communities,” says Hsieh. “It’s sprung up collaborations with groups ranging from high-pressure chemists to Martian paleomagnetists to quantum materials scientists.”

Researchers from Berkeley Lab; UC Berkeley; Ludwig-Maximilian University of Munich, Germany; Iowa State University; Carnegie Institution of Washington, Washington, D.C.; and Ames Laboratory participated in the work.

Learn and see more: Tiny Quantum Sensors Watch Materials Transform Under Pressure



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An innovative pressure-sensing system for the next generation of smart materials

The two-component dye shows self-recovering mechanochromic luminescence that exhibits a high-contrast emission color change between violet and orange. CREDIT Yokohama National University

The building blocks of rationally designed chemicals are simple elements: carbon, hydrogen, oxygen and so on. These elements can be combined in myriad ways to accomplish a variety of chemicals with different characteristics. Even the same chemical can be treated differently – with pressure or heat, for example – to show drastically different properties. A simpler version is to think of how water can be boiled to cook pasta or frozen to become ice – the same ingredient can be made into two different states via temperature treatment.

Now, researchers are working to better control how the chemicals respond to treatment, as well as how to reverse the chemicals back to their original state with little to no interference. Such control would allow scientists to prepare the sensing systems of environmental stimuli, as well as continuously repeat the sensing.

A team of researchers at Yokohama National University has achieved such results with a specific compound that can emit light and has potential applications in the next generation of smart devices such as wearable devices and anti-counterfeiting paintings. They published their results online on September 12, ahead of print in Chemical Communications.

The compound is a derivative of thiophene, which is a dye with mechanochromic luminescence properties — it changes color under physical change. It starts emitting a violet glow under the irradiation of UV light, but as it is exposed to mechanical stimuli, such as grinding, the violet glow shifts slightly to blue. Another external intervention can make the compound heal and become violet again.

“Mechanochromically luminescent (MCL) dyes have recently attracted considerable interest on account of their potential applications,” said Suguru Ito, paper author and associate professor in the Department of Chemistry and Life Science in the Graduate School of Engineering Science at Yokohama National University. “However, it is still very difficult to rationally design MCL dyes with desired characteristics.”

In this study, however, researchers discovered that by adding another chemical called DMQA, the dye changed to orange under mechanical stimuli. The dye did not need more external stimuli to revert back to violet either.

“We combined two kinds of rational design guidelines for tuning the luminescent properties, resulting in the desired — and unprecedented– characteristics of high-contrast, self-recovering dyes,” Ito said.

The first rational design guideline is that the recovery behavior of the dye can be attributed to the length of the alkyl group in the compound — a longer chain of carbon atoms with hydrogens in the dye allows the dye to recrystallize and heal in time. The second is that by mixing with DMQA, the color range between the original state and ground state differ greatly.

“The next step is to establish a rational design guideline to control the dye’s responsiveness to mechanical stimuli,” Ito said. “My ultimate goal is to develop an innovative pressure-sensing system by rationally creating a material that can change its emission color in stages in response to mechanical stimuli of different intensity.”

With such control, Ito could use mechanical stimuli to precisely induce a specific and intended response. A little pressure could shift the violet glow to blue, a little more pressure pushes the glow closer to red. A system with such ability would allow for stepwise changes and recoveries by the stimulus, which could be highly beneficial in the next generation of smart materials, according to Ito.

Learn more: Researchers design tunable, self-recovering dyes for use in next-generation smart devices


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A squidlike robot that’s fast, quiet and hard to see

Xiaobo Bi and Qiang Zhu discuss their work developing an aquatic robot inspired by cephalopods. (Left) Envisioned squid-inspired robot that combines fin flapping and jetting for locomotion. (Right) Numerical simulations provide insights of the underlying physical mechanisms. CREDIT Qiang Zhu

Scientists studied fluid mechanics to simulate and build a squidlike robot that’s fast, quiet and hard to see.

Inspired by the unique and efficient swimming strategy of cephalopods, scientists developed an aquatic robot that mimics their form of propulsion.

These high-speed, squidlike robots are made of smart materials, which make them hard to detect — an advantage that has potential military reconnaissance and scientific applications — while maintaining a low environmental footprint.

Physicists Xiaobo Bi and Qiang Zhu used numerical simulations to illustrate the physical mechanisms and fluid mechanics of a squid’s swimming method, which uses intermittent bursts through pulsed jet propulsion. By using this form of locomotion, the new device can achieve impressive speeds, just like its animal inspiration. Bi and Zhu discuss their work in this week’s Physics of Fluids, from AIP Publishing.

When swimming, these squidlike machines suck water into a pressure chamber and then eject it. The soft-bodied device could be used as a platform for environmental monitoring by simultaneously using this feature to test water samples as it swims.

“In addition to the 2D and 3D numerical simulations presented in this article, we are working with an interdisciplinary team to build a prototype of the mechanical device, to perform both straight-line swimming and maneuvers,” Zhu said. “This project will combine fluid dynamics, control, smart materials and robotic design.”

The device could be used as either a stand-alone swimmer or as a propeller of an underwater vehicle.

The researchers have not yet been able to maintain speeds that can last for more than a few cycles due to turbulence and instabilities, but they are working on ways to overcome this. Zhu hopes this research will provide a starting point for more sophisticated modeling and experimental studies to develop robots like their creation.

Learn more: Squid-inspired robots might have environmental, propulsion applications


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Using CRISPR in a different way to create new materials

MIT engineers created a DNA-acrylamide gel that can be degraded by DNA-editing enzymes. At right, the gel is broken down after two hours of exposure to a DNA “trigger sequence.” At left, the gel is exposed to DNA that doesn’t contain the trigger sequence, so it remains intact. Image courtesy of the researchers

Smart materials change properties in response to specific DNA sequences; could be used in a variety of devices.

The CRISPR genome-editing system is best-known for its potential to correct disease-causing mutations and add new genes into living cells. Now, a team from MIT and Harvard University has deployed CRISPR for a completely different purpose: creating novel materials, such as gels, that can change their properties when they encounter specific DNA sequences.

The researchers showed they could use CRISPR to control electronic circuits and microfluidic devices, and to release drugs, proteins, or living cells from gels. Such materials could be used to create diagnostic devices for diseases such as Ebola, or to deliver treatments for diseases such as irritable bowel disease.

“This study serves as a nice starting point for showing how CRISPR can be utilized in materials science for a really wide range of applications,” says James Collins, the Termeer Professor of Medical Engineering and Science in MIT’s Institute for Medical Engineering and Science (IMES) and Department of Biological Engineering, and the senior author of the study.

The lead authors of the study, which appears in the Aug. 22 online edition of Science, are MIT graduate students Max Atti English, Luis Soenksen, and Raphael Gayet, and postdoc Helena de Puig.

DNA interactions

CRISPR is based on DNA-cutting proteins called Cas enzymes, which bind to short RNA guides that direct them to specific areas of the genome. Cas cuts DNA in those locations, deleting a gene or allowing new genetic sequences to be introduced.

Over the past several years, much research has been devoted to developing CRISPR as a gene-editing tool for treating disease by cutting out or repairing faulty genes. The MIT and Harvard team set out to adapt it for creating materials that could respond to external cues such as the presence of a certain sequence of DNA.

For this work, they used an enzyme known as Cas12a, which can be programmed to bind to specific sequences of double-stranded DNA by simply changing the guide RNA sequence that is given along with the enzyme. Once Cas12a encounters a target DNA sequence, also called a trigger, it cleaves the double-stranded DNA and transforms into an enzyme that can slice any single-stranded DNA it encounters.

“By incorporating DNA into materials, you can use this enzyme to control the properties of the materials in response to a specific biological cue in the environment,” English says.

The researchers took advantage of this to design gels that incorporate single-stranded DNA in key functional or structural roles. In one example, they created a gel made of polyethylene glycol (PEG) and used DNA to anchor enzymes or other large biomolecules to the gel. When activated by a trigger sequence, Cas12a cuts the DNA anchors, releasing the payload.

That type of gel could be useful for releasing therapeutic compounds such as drugs or growth factors, the researchers say. In another example, they created an acrylamide gel in which single-stranded DNA forms an integral part of the gel structure. In that case, when Cas12a is activated by the trigger, the entire gel breaks down, enabling the release of larger cargoes such as cells or nanoparticles.

“In that context, we consider the single-stranded DNA as a structural scaffold,” Gayet says. “The enzyme is able to catalyze the cleavage of the single-stranded DNA, which acts as a structural linker, and release all of those molecules.”

The researchers are now exploring the possibility of using this approach to deliver engineered bacterial cells to help treat gastrointestinal diseases.

Inexpensive diagnostics

The researchers also created two CRISPR-controlled diagnostic devices, one based on an electronic circuit and the other on a microfluidic chip.

To create the electronic circuit, the researchers designed a gel that includes single-stranded DNA and a material called carbon black, which conducts electricity. When attached to the surface of an electrode, this conductive gel allows electrical current to flow. However, if Cas12a is activated by a trigger sequence, such as a strand of viral DNA from a blood sample, the gel becomes detached from the electrode and current stops flowing.

For their microfluidic sensor, the researchers created a DNA-containing gel that acts as a valve that controls the flow of a solution through the microfluidic channel. If the solution contains a blood sample with a target DNA sequence, the gel breaks down, turning off the valve, and the solution stops flowing. This microfluidic sensor can be connected to an RFID chip, allowing it to wirelessly transmit the results of the test.

“A health care worker can be monitoring dozens of patients, and the presence or absence of the Ebola trigger will automatically relay a binary signal,” Soenksen says.

While the researchers used fluid samples containing Ebola virus RNA to test this approach, it could also be adapted to detect other infectious diseases, as well as cancer cells circulating in a patient’s bloodstream.

Philip LeDuc, a professor of mechanical engineering at Carnegie Mellon University, describes the work as “tremendously creative.”

“This is a very non-obvious intersection of two different fields, and the influence of this work will be far-reaching,” says LeDuc, who was not involved in the study. “This transdisciplinary work may enable an entire new generation of approaches for applications from building artificial organs to improving the environment.”

Learn more: Using CRISPR to program gels with new functions


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Real-time insight into wearers’ emotions provided by new smart materials

Wrist-worn private affective wearables can serve as a bridge between mind and body and can really help people connect to their feelings.
Muhammad Umair

Smart wearable technology that changes colour, heats up, squeezes or vibrates as your emotions are heightened has the potential to help people with affective disorders better control their feelings.

Researchers from Lancaster University’s School of Computing and Communications have worked with smart materials on wrist-worn prototypes that can aid people diagnosed with depression, anxiety, and bi-polar disorders in monitoring their emotions.

Wrist bands that change colour depending upon the level of emotional arousal allow users to easily see or feel what is happening without having to refer to mobile or desktop devices.

“Knowing our emotions and how we can control them are complex skills that many people find difficult to master,” said co-author Muhammad Umair, who will present the research at DIS 19 in San Diego.

“We wanted to create low-cost, simple prototypes to support understanding and engagement with real-time changes in arousal. The idea is to develop self-help technologies that people can use in their everyday life and be able to see what they are going through. Wrist-worn private affective wearables can serve as a bridge between mind and body and can really help people connect to their feelings.

“Previous work on this technologies has focused on graphs and abstract visualisations of biosignals, on traditions mobile and desktop interfaces. But we have focused on devices that are wearable and provide not only visual signals but also can be felt through vibration, a tightening feeling or heat sensation without the need to access other programmes – as a result we believe the prototype devices provide real-time rather than historic data.”

The researchers worked with thermochromic materials that change colour when heated up, as well as devices that vibrate or squeeze the wrist. Tests of the devices saw participants wearing the prototypes over the course of between eight and 16 hours, reporting between four and eight occasions each when it activated – during events such as playing games, working, having conversations, watching movies, laughing, relaxing and becoming scared.

Co-author Professor Corina Sas said: “Our prototypes capture physiological arousal. If we talk about sadness, then as this is associated with low arousal – or what we call emotional intensity – the device will most likely reflect low arousal. On the other hand, anxiety tends to be associated with high intensity arousal, so that device will most likely reflect this. The device does not differentiate between positive or negative emotions, but between high and low intensity ones.”

A skin response sensor picked up changes in arousal – through galvanic skin response, which measures the electrical conductivity of the skin – and represented it through the various prototype designs. Those smart materials which were both instant and constant and which had a physical rather than visual output, were most effective.

Muhammad added: “Participants started to pay attention to their in-the-moment emotional responses, realising that their moods had changed quickly and understanding what it was that was causing the device to activate. It was not always an emotional response, but sometimes other activities – such as taking part in exercise – could cause a reaction.

“One of the most striking findings was that the devices helped participants started to identify emotional responses which they had been unable to beforehand, even after only two days.

“We believe that a better understanding of the materials we employed and their qualities could open up new design opportunities for representing heightened emotions and allowing people a better sense of sense and emotional understanding.”

Professor Sas said: “We think there are a range of opportunities in both clinical and non-clinical settings for the devices, as most of us can benefit for being more aware and able to control or what we call regulate our emotional responses.

“The ability to be more in touch with one’s emotions and to regulate them is key for emotional well-being in general and mental health in particular.”

Learn more: Smart materials provide real-time insight into wearers’ emotions


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