NT/ Nano-sized islands open possibilities for the application of single-atom catalysts
Nanotechnology & nanomaterials biweekly vol.34, 18th October — 1st November
TL;DR
- A new method to anchor single atoms of platinum-group metals on nanometer-sized islands allows for the efficient using these expensive metals as catalysts for a wide variety of applications. Researchers showed that platinum atoms could be confined on small cerium-oxide islands within a porous material to catalyze reactions without sticking to each other, which has been a major stumbling block for their use.
- Researchers created a technique for precisely arranging nanoparticles onto surfaces in arrays with arbitrary shapes that do not cause damage to the material’s surface. The scalable technique could help make higher-performance devices like lasers, LEDs, sensors, and actuators.
- A group of researchers proposed a novel two-dimensional (2D) nanoconfinement strategy to strongly enhance the oxygen evolution reaction (OER) activity of low-conductivity metal-organic frameworks (MOFs). Results were published in Nature Communications.
- Researchers have made a significant advance in the way they produce exotic open-framework superlattices made of hollow metal nanoparticles. The new method for preparing open-framework colloidal crystals leads to the synthesis of 12 novel nanoparticle superlattices.
- A UNSW paper published recently in Nature Reviews Materials presents an exciting overview of the emerging field of 2D ferroelectric materials with layered van der Waals crystal structures, a novel class of low-dimensional materials that are highly interesting for future nanoelectronics.
- By the end of 2021, scientists had presented perovskite silicon tandem solar cells with an efficiency of close to 30 percent. This value was a world record for eight months, a long time for this hotly contested field of research. Scientists now describe how they achieved this record value with nano-optical structuring and reflective coatings.
- Northwestern University researchers have uncovered a previously unknown property of colloidal crystals, highly ordered three-dimensional arrays of nanoparticles.
- In a study of one-dimensional electron correlation states at the MTB of monolayer and bilayer MoSe2, a research team found that two types of correlated insulating states driven by a dubbed Hubbard-type Coulomb blockade effect could be switched by tip pulses.
- The bacteria, such as the pathogenic bacterium Pseudomonas aeruginosa, are often persistent and defy the body’s own immune system or chemical biocides. Current research approaches are therefore trying to prevent bacterial colonization of material surfaces or at least to make it more difficult. A team from Johannes Gutenberg University Mainz (JGU) and the German Federal Institute of Hydrology (BfG) in Koblenz has now developed a new approach using ceria nanoparticles.
- In an article published in Nanoscale, NIST researchers reviewed the many facets of nucleic acid nanotechnology (NAN) and concluded that the technology holds the most promise for bridging the world of biology and semiconductors.
- And more!
Nanotech Market
Nanotechnology deals with the ability to see, understand, measure, predict, produce or control matter at the nanoscale (below 100 nanometers). The realm of nanotechnology lies between 0.1 and 100 nanometers, wherein a nanometer is defined as one-thousandth of a micron. As a versatile technology with widespread applications in a wide range of end-use sectors, nanotechnology is currently facing a mixed bag of challenges and opportunities as the COVID-19 pandemic continues to spread across the globe. With the world fighting its biggest public health crisis in history, nanotechnology healthcare applications are storming into the spotlight led by the focus on nano intervention in terms of designing effective ways to identify, diagnose, treat and eliminate the spread of COVID-19 infections. Their role as nanocarriers has the potential to design risk-free and effective immunization strategies. In the post-COVID-19 period, the use of nanotechnology solutions in the production of a multitude of devices & products will continue to grow.
Amid the COVID-19 crisis, the global market for Nanotechnology estimated at US$42.2 Billion in the year 2020, is projected to reach a revised size of US$70.7 Billion by 2026, growing at a CAGR of 9.2% over the analysis period. Nanocomposites, one of the segments analyzed in the report, is projected to record a 8.7% CAGR and reach US$35.4 Billion by the end of the analysis period. After a thorough analysis of the business implications of the pandemic and its induced economic crisis, growth in the Nanomaterials segment is readjusted to a revised 10.1% CAGR for the next 7-year period.
Global nanotechnology market to reach US $126.8 billion by the year 2027. Amid the COVID-19 crisis, the global market for Nanotechnology is estimated at US $54.2 billion in the year 2020, and is projected to reach a revised size of US $126 billion.
Latest News & Research
Functional CeOx nanoglues for robust atomically dispersed catalysts
by Xu Li, Xavier Isidro Pereira-Hernández, Yizhen Chen, Jia Xu, Jiankang Zhao, Chih-Wen Pao, Chia-Yu Fang, Jie Zeng, Yong Wang, Bruce C. Gates, Jingyue Liu in Nature
A new method to anchor single atoms of platinum-group metals on nanometer-sized islands allows for efficiently using these expensive metals as catalysts for a wide variety of applications.
Reporting in the journal Nature, researchers showed that platinum atoms could be confined on small cerium-oxide islands within a porous material to catalyze reactions without sticking to each other, which has been a major stumbling block for their use. The study was led by Arizona State University Professor Jingyue Liu, University of California, Davis, Professor Bruce Gates and Washington State University Professor Yong Wang.
“The stabilization of precious metals to allow each atom to be a catalyst is a holy grail in the catalysis field,” said Wang, Regents Professor in WSU’s Gene and Linda Voiland School of Chemical Engineering and Bioengineering and a laboratory fellow at Pacific Northwest National Laboratory. “We are not only using the least amount of platinum group metals but are also making each atom much more reactive.”
Catalysts, which speed up chemical reactions, are key to the technologies used in making chemicals and fuels and for cleaning up pollutants, including exhaust from cars, trucks and fossil fuel power plants. Many catalysts contain precious metals such as platinum, rhodium and palladium, which are extremely expensive.
Researchers in the early 1990s began investigating how to isolate metal atoms as catalysts, but they hadn’t been able to stabilize them at the high temperatures required for catalytic converters and other practical applications. Once the metal atoms are exposed to the conditions required for reactions, they tend to clump together.
The research team solved the problem by dispersing the metal atoms within the nanometer-sized islands of cerium oxide. The numerous islands lie on commercial silicon-dioxide support that is widely used in many common catalytic reactions, but the metal atoms are excluded from the support. With its extremely high surface area, silicon dioxide is able to anchor a very large number of the islands holding the metal atoms within a small volume. The cerium oxide sticks like glue to the silicon dioxide and holds the individual metal atoms tightly so that they don’t wander off to find each other, clump and become ineffective.
The researchers found that the island-confined metal atoms were stable in catalyzing reactions under both oxidative and reductive conditions. Oxidation, in which oxygen is added to a substance, is used in emission control technology to remove harmful carbon monoxide and unburned hydrocarbons. Reduction, in which hydrogen is present and reacts with other molecules, is used for many industrial applications, including to produce fuels, fertilizers and drugs.
“The atomic precision of the manufacture of the new catalysts may open avenues to design catalysts with unprecedented flexibility in the placement of targeted numbers of atoms on each island,” said Gates. “That allows us to investigate the reactivity and identify the most reactive species — to find out which structures and configurations are most efficient.”
The researchers hope to further study the approach for a wide range of catalytic applications.
“This work gives the scientific community a new tool in the toolkit to understand the catalytic site requirement for specific reactions of interest and for developing highly active and stable new catalysts,” said Liu. “It creates tremendous opportunities for catalytic technology and takes atomically dispersed metal catalysts one major step closer to practical applications.”
Nanoparticle contact printing with interfacial engineering for deterministic integration into functional structures
by Weikun Zhu, Peter F. Satterthwaite, Patricia Jastrzebska-Perfect, Roberto Brenes, Farnaz Niroui in Science Advances
Researchers at MIT have developed a technique for precisely controlling the arrangement and placement of nanoparticles on a material, like the silicon used for computer chips, in a way that does not damage or contaminate the surface of the material.
The technique, which combines chemistry and directed assembly processes with conventional fabrication techniques, enables the efficient formation of high-resolution, nanoscale features integrated with nanoparticles for devices like sensors, lasers, and LEDs, which could boost their performance.
Transistors and other nanoscale devices are typically fabricated from the top down — materials are etched away to reach the desired arrangement of nanostructures. But creating the smallest nanostructures, which can enable the highest performance and new functionalities, requires expensive equipment and remains difficult to do at scale and with the desired resolution.
A more precise way to assemble nanoscale devices is from the bottom up. In one scheme, engineers have used chemistry to “grow” nanoparticles in solution, drop that solution onto a template, arrange the nanoparticles, and then transfer them to a surface. However, this technique also involves steep challenges. First, thousands of nanoparticles must be arranged on the template efficiently. And transferring them to a surface typically requires a chemical glue, large pressure, or high temperatures, which could damage the surfaces and the resulting device.
The MIT researchers developed a new approach to overcome these limitations. They used the powerful forces that exist at the nanoscale to efficiently arrange particles in the desired pattern and then transfer them to a surface without any chemicals or high pressures, and at lower temperatures. Because the surface material remains pristine, these nanoscale structures can be incorporated into components for electronic and optical devices, where even minuscule imperfections can hamper performance.
“This approach allows you, through engineering of forces, to place the nanoparticles, despite their very small size, in deterministic arrangements with single-particle resolution and on diverse surfaces, to create libraries of nanoscale building blocks that can have very unique properties, whether it is their light-matter interactions, electronic properties, mechanical performance, etc.,” says Farnaz Niroui, the EE Landsman Career Development Assistant Professor of Electrical Engineering and Computer Science (EECS) at MIT, a member of the MIT Research Laboratory of Electronics, and senior author on a new paper describing the work. “By integrating these building blocks with other nanostructures and materials we can then achieve devices with unique functionalities that would not be readily feasible to make if we were to use the conventional top-down fabrication strategies alone.”
The research is published in Science Advances. Niroui’s co-authors are lead author Weikun “Spencer” Zhu, a graduate student in the Department of Chemical Engineering, as well as EECS graduate students Peter F. Satterthwaite, Patricia Jastrzebska-Perfect, and Roberto Brenes.
To begin their fabrication method, known as nanoparticle contact printing, the researchers use chemistry to create nanoparticles with a defined size and shape in a solution. To the naked eye, this looks like a vial of colored liquid, but zooming in with an electron microscope would reveal millions of cubes, each just 50 nanometers in size. (A human hair is about 80,000 nanometers wide.)
The researchers then make a template in the form of a flexible surface covered with nanoparticle-sized guides, or traps, that are arranged in the shape they want the nanoparticles to take. After adding a drop of nanoparticle solution to the template, they use two nanoscale forces to move the particles into the right position. The nanoparticles are then transferred onto arbitrary surfaces.
At the nanoscale, different forces become dominant (just like gravity is a dominant force at the macroscale). Capillary forces are dominant when the nanoparticles are in liquid and van der Waals forces are dominant at the interface between the nanoparticles and the solid surface they are in contact with. When the researchers add a drop of liquid and drag it across the template, capillary forces move the nanoparticles into the desired trap, placing them precisely in the right spot. Once the liquid dries, van der Waals forces hold those nanoparticles in position.
“These forces are ubiquitous and can often be detrimental when it comes to the fabrication of nanoscale objects as they can cause the collapse of the structures. But we are able to come up with ways to control these forces very precisely to use them to control how things are manipulated at the nanoscale,” says Zhu.
They design the template guides to be the right size and shape, and in the precisely proper arrangement so the forces work together to arrange the particles. The nanoparticles are then printed onto surfaces without a need for any solvents, surface treatments, or high temperatures. This keeps the surfaces pristine and properties intact while allowing yields of more than 95 percent. To promote this transfer, the surface forces need to be engineered so that the van der Waals forces are strong enough to consistently promote particles to release from the template and attach to the receiving surface when placed in contact.
The team used this technique to arrange nanoparticles into arbitrary shapes, such as letters of the alphabet, and then transferred them to silicon with very high position accuracy. The method also works with nanoparticles that have other shapes, such as spheres, and with diverse material types. And it can transfer nanoparticles effectively onto different surfaces, like gold or even flexible substrates for next-generation electrical and optical structures and devices.
Their approach is also scalable, so it can be extended to be used toward the fabrication of real-world devices.
Niroui and her colleagues are now working to leverage this approach to create even more complex structures and integrate them with other nanoscale materials to develop new types of electronic and optical devices.
Open-channel metal particle superlattices
by Yuanwei Li, Wenjie Zhou, Ibrahim Tanriover, Wisnu Hadibrata, Benjamin E. Partridge, Haixin Lin, Xiaobing Hu, Byeongdu Lee, Jianfang Liu, Vinayak P. Dravid, Koray Aydin, Chad A. Mirkin in Nature
Researchers from Northwestern University have made a significant advance in the way they produce exotic open-framework superlattices made of hollow metal nanoparticles.
Using tiny hollow particles termed metallic nanoframes and modifying them with appropriate sequences of DNA, the team found they could synthesize open-channel superlattices with pores ranging from 10 to 1,000 nanometers in size — sizes that have been difficult to access until now. This newfound control over porosity will enable researchers to use these colloidal crystals in molecular absorption and storage, separations, chemical sensing, catalysis and many optical applications.
The new study identifies 12 unique porous nanoparticle superlattices with control over symmetry, geometry and pore connectivity to highlight the generalizability of new design rules as a route to making novel materials.
Chad A. Mirkin, the George B. Rathmann Professor of Chemistry in the Weinberg College of Arts and Sciences at Northwestern and director of the International Institute for Nanotechnology, said the new findings will have broad-ranging impacts in nanotechnology and beyond.
“We had to rethink what we knew about DNA bonding with colloidal particles,” said Mirkin, who led the research. “With these new types of hollow nanocrystals, the existing rules for crystal engineering were not adequate. Nanoparticle assembly driven by ‘edge-bonding’ allows us to access a breadth of crystalline structures that we cannot access through conventional ‘face-bonding,’ the traditional way we think of structure formation in this field. These new structures lead to new opportunities both from scientific and technological standpoints.”
A leader in nanochemistry, Mirkin is also a professor of chemical and biological engineering, biomedical engineering and materials science and engineering in the McCormick School of Engineering and a professor of medicine at Northwestern University Feinberg School of Medicine.
Mirkin’s team has been using the programmability of DNA to synthesize crystals with unusual and useful properties for over two decades; broadening the concept to include hollow particles is a big step toward a more universal approach to understanding and controlling colloidal crystal formation.
Nature uses colloidal crystals to control colors of organisms, including butterfly wings and the changeable color in the skin of a chameleon. Mirkin’s laboratory-generated structures — especially the porous ones, through which molecules, materials and even light can travel — will challenge scientists and engineers to create new devices from them.
Vinayak Dravid, the Abraham Harris Professor of Materials Science and Engineering at McCormick and an author of the paper, added that many industrial chemical processes rely on zeolites, another class of synthetic porous materials.
“There are many limitations to zeolites because these are made by physical rules that limit options,” Dravid said. “But when DNA is used as a bond, it allows for a greater diversity of structures and much larger variety of pore sizes, and thus a diverse range of properties.”
The ability to control pore size and connections between pores opens a range of potential uses. For example, the authors show that porous superlattices exhibit an interesting optical behavior called a negative refractive index not found in nature and only accessible with engineered materials.
“In this work, we discovered how open-channel superlattices can be new types of optical metamaterials that allow for a negative index of refraction,” said Koray Aydin, also an author on the paper and an associate professor of electrical and computer engineering in McCormick. “Such metamaterials enable exciting applications such as cloaking and superlensing, the imaging of super small objects with microscopy.”
The researchers are continuing to collaborate to drive the work forward.
“We need to apply these new design rules to nanoporous metallic structures made of others metals, like aluminum, and we need to scale the process,” Mirkin said. “These practical considerations are very important in the context of high-performance optical devices. Such an advance could be truly transformative.”
Nano-optical designs for high-efficiency monolithic perovskite–silicon tandem solar cells
by Philipp Tockhorn, Johannes Sutter, Alexandros Cruz, Philipp Wagner, Klaus Jäger, Danbi Yoo, Felix Lang, Max Grischek, Bor Li, Jinzhao Li, Oleksandra Shargaieva, Eva Unger, Amran Al-Ashouri, Eike Köhnen, Martin Stolterfoht, Dieter Neher, Rutger Schlatmann, Bernd Rech, Bernd Stannowski, Steve Albrecht, Christiane Becker in Nature Nanotechnology
By the end of 2021, teams at HZB had presented perovskite silicon tandem solar cells with an efficiency close to 30 percent. This value was a world record for eight months, a long time for this hotly contested field of research. In the renowned journal Nature Nanotechnology, the scientists describe how they achieved this record value with nanooptical structuring and reflective coatings.
Tandem solar cells made of perovskite and silicon enable significantly higher efficiencies than silicon solar cells alone. Tandem cells from HZB have already achieved several world records. Most recently, in November 2021, HZB research teams achieved a certified efficiency of 29.8 % with a tandem cell made of perovskite and silicon. This was an absolute world record that stood unbeaten at the top for eight months. It was not until the summer of 2022 that a Swiss team at EPFL succeeded in surpassing this value.
Three HZB teams had worked closely together for the record-breaking tandem cell. Now they present the details in Nature Nanotechnology. The journal also invited them to write a research briefing, in which they summarise their work and give an outlook on future developments.
“Our competences complement each other very well,” says Prof. Dr. Christiane Becker, who developed the world record cell with the team led by Dr. Bernd Stannowski (silicon bottom cell) and Prof. Dr. Steve Albrecht (perovskite top cell). Becker’s team introduced a nanooptical structure into the tandem cell: a gently corrugated nanotexture on the silicon surface. “Most surprising, this texture brings several advantages at once: it reduces reflection losses and ensures a more regular perovskite film formation,” says Becker. In addition, a dielectric buffer layer on the back of the silicon reduces parasitic absorption at near-infrared wavelengths.
As conclusion, the researchers hold: customised nanotextures can help to improve perowskite semiconductor materials on diverse levels. These results are not only valuable for tandem solar cells made of perovskite and silicon, but also for perovskite-based light-emitting diodes.
Exceptional catalytic activity of oxygen evolution reaction via two-dimensional graphene multilayer confined metal-organic frameworks
by Siliu Lyu et al in Nature Communications
Prof. Zhang Tao’s group at the Ningbo Institute of Materials Technology and Engineering (NIMTE) of the Chinese Academy of Sciences (CAS), in collaboration with Prof. Hou Yang from Zhejiang University and Prof. Xiao Jianping from the Dalian Institute of Chemical Physics of CAS, proposed a novel two-dimensional (2D) nanoconfinement strategy to strongly enhance the oxygen evolution reaction (OER) activity of low-conductivity metal-organic frameworks (MOFs). Results were published in Nature Communications.
The development of high-efficiency electrocatalysts for the electrochemical conversion of water to generate environmentally friendly and sustainable hydrogen energy has drawn tremendous attention for decades.
Despite the crucial role the OER plays in water splitting, OER at the anode requires a relatively high thermodynamic potential to accelerate water splitting kinetics. Thanks to the large surface area, tunable porosity, diverse compositions and metal centers, MOFs have emerged as promising candidates for efficient OER electrocatalysts. However, the intrinsically poor conductivity of most MOFs seriously impedes their catalytic activity.
To address this issue, researchers at NIMTE proposed an electrochemical strategy to confine MOFs between graphene multilayers via the two-electrode electrochemical system, thus endowing poorly conductive MOFs with strongly enhanced catalytic performance.
The as-prepared NiFe-MOF//G shows a remarkably low overpotential of 106 mV to reach 10 mA cm-2, surpassing the pristine NiFe-MOF as well as other previously reported MOFs and their derivatives. Besides, the NiFe-MOF//G electrode is highly stable, which can retain the performance for more than 150 h at 10 mA cm-2 without obvious activity decay.
Notably, the results of X-ray absorption spectroscopy experiments and density-functional theory calculations indicate that the nanoconfinement from graphene multilayers optimizes the electronic structure and catalysis center of MOF materials with the formation of highly reactive NiO6-FeO5 distorted octahedral species in MOF structure. In addition, the nanoconfinement lowers the limiting potential for water oxidation reaction.
The nanoconfinement strategy can be applied to other varied MOFs with different structures, greatly improving their electrocatalytic activities. Meanwhile, this work challenges the common conception of pristine MOFs as inert catalysts and reveals the great application potential of poorly conductive or even insulating MOFs in electrocatalysis applications.
Ferroelectric order in van der Waals layered materials
by Dawei Zhang et al in Nature Reviews Materials
A UNSW paper published recently in Nature Reviews Materials presents an exciting overview of the emerging field of 2D ferroelectric materials with layered van der Waals crystal structures, a novel class of low-dimensional materials that is highly interesting for future nanoelectronics.
Future applications include ultra-low energy electronics, high-performance, non-volatile data-storage, high-response optoelectronics, and flexible (energy-harvesting or wearable) electronics.
Structurally different from conventional oxide ferroelectrics with rigid lattices, van der Waals (vdW) ferroelectrics have stable layered structures with a combination of strong intralayer and weak interlayer forces.
These special atomic arrangements, in combination with the ferroelectric order, give rise to fundamentally new phenomena and functionalities not found in conventional materials.
“Fundamentally new properties are found when these materials are exfoliated down to atomically thin layers,” says author Dr. Dawei Zhang. “For example, the origin of the polarization and the switching mechanisms for the polar order can be different from conventional ferroelectrics, enabling new material functionality.”
One of these material’s most intriguing aspects is their easily stackable nature because of the weak van der Waals interlayer bonds, which means that vdW ferroelectrics are readily integrable with highly dissimilar crystal-structure materials, such as industrial silicon substrates, without interfacial issues.
“This makes them highly attractive as building blocks for post-Moore’s law electronics,” says author Prof. Jan Seidel, also at UNSW.
From the perspective of applications and novel functionalities, vdW ferroelectrics present a wide range of opportunities for nanoelectronics owing to their easily obtainable ferroelectricity at the nanoscale, and dangling bonds-free, clean vdW interfaces that facilitate CMOS-compatible (current silicon technology) integration.
The new review discusses experimentally verified vdW ferroelectric systems and their unique characteristics, such as quadruple-well potentials, metallic ferroelectricity and dipole-locking effects. It also discusses engineered vdW ferroelectricity in stacks of otherwise nonpolar parent materials created by artificially breaking centrosymmetry.
Additionally, innovative device applications harnessing vdW ferroelectricity are showcased, including electronic transistors able to beat the fundamental thermodynamic limits, non-volatile memories and optoelectronic and flexible devices. Recent progress and existing challenges provide a perspective on future research directions and applications.
“It’s a relatively new field, so there are still many challenges that need to be solved to realize the full technological potential of these materials,” says author Dr. Pankaj Sharma. “For example, we need to address large-area, uniform, wafer scale growth, and integration methods. These will allow development of futuristic low-energy electronics and computing solutions.”
Given the recent emergence of vdW ferroelectrics, the materials library of such systems is quickly evolving. This leaves room for new developments, such as multiferroicity and coupled functionalities of multiple orders, for example ferroelectricity and magnetism, and the functionality of domain walls in such materials.
Shape memory in self-adapting colloidal crystals
by Seungkyu Lee, Heather A. Calcaterra, Sangmin Lee, Wisnu Hadibrata, Byeongdu Lee, EunBi Oh, Koray Aydin, Sharon C. Glotzer, Chad A. Mirkin in Nature
Northwestern University researchers have uncovered a previously unknown property of colloidal crystals, highly ordered three-dimensional arrays of nanoparticles.
The team engineered colloidal crystals with complementary strands of DNA and found that dehydration crumpled the crystals, breaking down the DNA hydrogen bonds. But when researchers added water, the crystals bounced back to their original state within seconds.
The new study describes the shape memory that occurs after changes to a colloidal crystal’s structure and that is not accessible in other types of crystals. In response to external stimuli, reversible structural changes in these new materials could lead to associated dynamic functional changes that make them useful in chemical and biological sensing, optics and soft robotics.
“The deformed crystal has completely different properties when it’s broken down,” said Northwestern’s Chad A. Mirkin, who led the study. “But DNA retraces its steps. Imagine if a house was destroyed by a hurricane, but then that every nail and board returned to their original places to reform the house after the storm passed. That’s essentially equivalent to what is happening here with these crystals at the nanoscale.”
A nanotechnology pioneer, Mirkin is the George B. Rathmann Professor of Chemistry in the Weinberg College of Arts and Sciences at Northwestern and director of the International Institute for Nanotechnology. Mirkin also is a professor of chemical and biological engineering, biomedical engineering and materials science and engineering in the McCormick School of Engineering and a professor of medicine in Northwestern University’s Feinberg School of Medicine.
The new property, which is a type of “hyperelasticity coupled with shape memory,” is controlled by the particle-interconnecting DNA’s specific sequence and influences the object’s structure and compressibility. Because of the crystal’s plasticity, it can break down and then come back together.
The discovery builds on work that Mirkin began in 1996. At the time, his research group reported how DNA could be used as a sequence-encoded bonding material, a glue that can be used to build colloidal crystals — some of which have structures and properties akin to conventional crystals found in nature, while others have structures and properties that have never been found in nature.
In the manuscript, the authors describe a new way of making crystals much larger than have ever been made before — ones large enough that they can be observed with the naked eye. In addition to enabling the shape memory discovery, this development has allowed these researchers to uncover new ways to use crystals as force and chemical detectors. Mirkin said he’s excited to see how the shape memory property of these crystals will be used, for example, in flow sensors in microscale fluidic devices and in detectors for chemical and biological molecules. Mirkin also is considering ways to use the unique crystals to make materials capable of withstanding extraordinary damage and rebounding back to their original states.
“These are remarkable materials — even damage to skin, which has an innate and remarkable ability to regenerate, leaves scars,” Mirkin said. “In this case that doesn’t happen. The DNA code in these crystals guides them back to their original states. This ability could aid in controlling chemical reactions and creating new classes of light switches, where ‘on’ is the conventional crystal, and ‘off’ is the deformed one, triggered by tiny changes in flow and force.”
Manipulating Hubbard-type Coulomb blockade effect of metallic wires embedded in an insulator
by Xing Yang et al in National Science Review
In a study of one-dimensional electron correlation states at the MTB of monolayer and bilayer MoSe2, a research team found that two types of correlated insulating states driven by a dubbed Hubbard-type Coulomb blockade effect could be switched by tip pulses.
By means of molecular beam epitaxy, this team has grown single-layer and double-layer MoSe2 films with one-dimensional MTB on graphene substrates. It is found by scanning tunneling microscopy that the one-dimensional MTB has metallic states. Due to its limited length, the one-dimensional states are subject to quantum confinement effect, resulting in quantized discrete energy levels.
They found two types of MTBs with different ground states, defined as in-phase and out-of-phase states respectively, according to the spatially modulated phase of the two discrete levels spanning the Fermi surface. More interestingly, by applying tip pulses, it is possible to reversibly switch the two states.
They showed that the Coulomb energies, determined by the wire length, drive the MTB into two types of ground states with distinct respective charge orders. The quantum well states at the Fermi surface are affected by the Coulomb effect.
When the Fermi surface is between two quantum-well states with different wave vectors, that is, the out-of-phase state, the energy level interval increases and becomes the sum of Coulomb energy and the interval of the quantum well states.
When a quantum well is exactly at the Fermi surface, that is, the in-phase state, the energy level is spin–split by Coulomb energy to form a single electron occupation, and the splitting size is the Coulomb energy.
The electron filling of MTB is tuned with the tip pulse, where the additional injected charges, as substantiated by first-principle calculations, are stabilized via a polaronic process, rendering it feasible to controllably adjust its number of electrons and its spin state.
The determined Coulomb energies are found to solely depend on the wire length, irrespective of the distance of the MTB to the graphene substrate, demonstrating the Coulomb interaction is short-range. This is different from the classical Coulomb blockade effect, where the Coulomb energy depends on its capacitance to the environment and is thus long-range.
Such short-range Coulomb energy has a similar expression to the classical Coulomb blockade effect, and is thus dubbed Hubbard-type Coulomb blockade effect.
This research team achieved control of electron correlation and spin states at the atomic scale, laying a foundation for understanding and tailoring correlated physics in complex systems.
Communication Breakdown: Into the Molecular Mechanism of Biofilm Inhibition by CeO2 Nanocrystal Enzyme Mimics and How It Can Be Exploited
by Eva Pütz et al in ACS Nano
Bacteria love moist surfaces. Once they have settled there, they do not live as solitary organisms but form larger communities that are embedded in a protective film. These biofilms are found on various surfaces, for example at home on light switches, in the bathroom, on toys or keyboards, on shopping carts, or ATMs that many people touch with their hands. This can lead to contact infections. The bacteria, such as the pathogenic bacterium Pseudomonas aeruginosa, are often persistent and defy the body’s own immune system or chemical biocides. Current research approaches are therefore trying to prevent bacterial colonization of material surfaces or at least to make it more difficult. A team from Johannes Gutenberg University Mainz (JGU) and the German Federal Institute of Hydrology (BfG) in Koblenz has now developed a new approach using ceria nanoparticles.
For bacterial life in communities, it is important that the individual cells “talk” to each other. Communication proceeds nonverbally with the help of signaling molecules that are continuously emitted to the environment, whereby different “languages” and “dialects” can occur depending on the specific bacterium.
As bacterial concentration increases so does the concentration of the signaling molecules. This allows bacteria to detect the number of other bacteria in their environment and activate processes that enable the formation of biofilms. To prevent colonization with bacterial biofilms, various hosts defend themselves with a strategy that “silences” the bacteria by enzymatically modifying the signaling molecules.
This is done, for example, with the help of haloperoxidases, a group of enzymes that halogenate signaling molecules through a complex reaction chain. These modified signaling molecules have a similar structure as the original molecules and can still bind to receptors. However, they can no longer activate the process chains that lead to biofilm formation.
This interference in bacterial gene regulation is also of pharmacological interest, because pathogenic bacteria can evade the attack of the immune defense or the effect of antibiotics by forming biofilms.
The researchers from Mainz and Koblenz mimic these processes with nanoparticles of cerium dioxide (CeO2). CeO2 nanoparticles are, as the researchers explain in their recent article in ACS Nano, a functional substitute for haloperoxidase enzymes.
However, the molecular mechanisms underlying biofilm inhibition are difficult to unravel in detail, because not only do many competitive reactions occur in bacterial cultures, but vast numbers of other biomolecules are also present in addition to the halogenated signaling molecules. The cooperation partners from Mainz and Koblenz demonstrate the enzyme-analog catalytic participation of the CeO2 nanoparticles via an analysis of the reaction cascade at the molecular level.
The halogenated signaling molecules were first identified in model reactions. In bacterial cultures, their detection was not possible directly because the products are being degraded too quickly. However, chromatographic workup and mass spectrometric analysis unexpectedly revealed the formation of further halogenated signaling molecules from the family of so-called quinolones.
This shows that the CeO2 nanoparticles interfere with biological processes just like native enzymes by modifying and inactivating signaling molecules.
“Cerium dioxide is non-toxic, chemically very stable, and it is contained, for example, in modern vehicle exhaust catalytic converters,” stated Dr. Eva Pütz, who carried out her doctoral thesis on this project. She is convinced that cerium dioxide is a viable and cost-effective alternative to conventional biocides.
“One practical application of our findings is to block bacterial growth and prevent bacterial infections,” she said. The quinolone signaling molecules lead to the formation of small colony variants in the multidrug-resistant bacterium Staphylococcus aureus, which are often diagnostically undetectable. “Since the halogenated quinolone signal molecules suppress colony formation, dangerous infections by P. aeruginosa and S. aureus, for example, can be prevented with the help of paint dispersions containing CeO2 nanoparticles,” added Dr. Athanasios Gazanis, who investigated the microbiological aspects in his doctoral thesis.
“Here we have an environmentally compatible component for a new generation of antibacterial surfaces that mimic nature’s defense system. Most importantly, it works not only in the lab, but also in everyday use,” said Nils Keltsch, who performed the biological trace analysis in his doctoral thesis.
The danger in combating biofilms with biocides and antibiotics is the formation of resistance. However, this could be effectively circumvented in an environmentally friendly way by coating polymers with CeO2 nanoparticles.
Synthesizing the biochemical and semiconductor worlds: the future of nucleic acid nanotechnology
by Jacob M. Majikes et al in Nanoscale
In an article published in Nanoscale, NIST researchers J. Alexander Liddle and Jacob Majikes reviewed the many facets of NAN and concluded that the technology holds the most promise for bridging the world of biology and semiconductors.
Trapped in a microscopic cage made of strands of DNA, molecules of a life-saving drug course through the bloodstream of a cancer patient. Only when receptors on the strands since they’ve arrived at the right location — cancer cells overproducing a particular protein or exhibiting other abnormal behavior — does the cage pop open, delivering the anti-cancer drug exactly where it’s needed and leaving the patient’s healthy cells unscathed.
That’s an example of how nucleic acid nanotechnology (NAN) on its own — using solely the physical and chemical properties of the nucleic acids DNA and RNA rather than the genetic code they carry — are revolutionizing medicine.
But what if the unique properties of DNA and RNA could be combined with the myriad advantages of semiconductor technology? For instance, researchers are developing an artificial nose by attaching arrays of miniature DNA molecular sensors — each one customized to sense a different molecule — to silicon chips. This bio-electronic sensor will have the capability to “sniff out” thousands of different chemicals in the body or the environment.
Some researchers and funding agencies, they noted, expected that NAN might supplant many aspects of semiconductor fabrication and could rival existing technologies for uses such as archival memory. Some scientists have suggested that the strands could efficiently self-assemble to build integrated circuits.
However, these endeavors are simply not economically viable, Majikes and Liddle asserted. Advances in the semiconductor industry over the past two decades have enabled rapid and inexpensive fabrication of the circuits without NAN. Although the intriguing possibilities that NAN offers have inspired and attracted researchers worldwide, economics must be considered when predicting the impact of this nanotechnology, the researchers emphasized.
Funding agencies judging the future utility of NAN should also factor in the large percentage of defects — assembly errors — inherent in DNA structures, Majikes and Liddle said. Defectively assembled proteins may make up as 30 percent of those in organisms. In the body, that’s not a problem; defective proteins are recycled and damaged DNA is repaired. But the semiconductor industry cannot tolerate defects at a level larger than one part in a trillion.
The high proportion of defects makes NAN a poor choice for fabricating electronic devices using the standard “bottom up” approach — starting with strands of DNA and building them to make larger, more complex devices — Liddle and Majikes noted. Instead, the most promising applications of NAN will emerge by combining strands of DNA or RNA with existing biological, pharmaceutical, and electronic devices, the NIST researchers predicted.
Integrating NAN and semiconductor technology may produce biosensors that could be monitored and controlled by smartphones, and enable detection of chemicals in the body and the environment with unparalleled sensitivity.
NAN offers these possibilities because strands of DNA readily bind to each other and a host of other molecules in predictable, controllable ways.
The versatility of DNA lies in its structure, the famous twisted ladder or double helix. Two long parallel chains of sugar and phosphate molecules form the rails of the ladder, while the rungs consist of pairs of molecules called bases. The arrangement of the bases, of which there are only four, encodes the blueprint for life but the bases can be switched out or replaced to create structures that have different sensitivities to a panoply of chemicals.
The bases and sugars along a DNA strand stay attached to each other because they share one or more pairs of electrons, a partnership is known as covalent bonding. By replacing a single base with a chemical anchor, often at one end of a strand, the remaining DNA structure can use covalent bonding to attach to a molecule connected to a particle of gold or a semiconductor device. Indeed, the industry has for years manufactured artificial DNA strands, each tailored to attach to a different group of molecules.
Although the double-stranded helix, which is strong and rigid, is the most familiar form of DNA, it also can take the form of single strands, which are floppy and loose. Fitting together like Legos, chains of single and double strands can then assume a variety of shapes that move and vibrate.
These characteristics enable a DNA-based structure to match with a cancer cell or other target “because we can easily engineer both the shape and flexibility of the structure so that it fits where we want it to on a protein or nanoparticle, or cell, and also keep it from fitting places where we don’t want it to go,” Majikes noted.
“We now see DNA strands as the ‘glue’ that could hold together and integrate many existing biological, pharmaceutical, and electronic devices and capabilities,” Majikes said. “These products will be wildly diverse but will generally make drugs smarter and make electronic sensors more nuanced and molecule specific,” he added. “NAN is essentially a universal connector between almost any nanoscale tools, whether they’re proteins, nanoparticles or electrodes.”
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