Georgia Tech Research Institute (GTRI) scientists work in an optical lab developing improved ion traps that could be used in quantum computing. Shown are (l-r) research scientists Jason Amini and Nicholas Guise. (Credit: Rob Felt)
“To write down the quantum state of a system of just 300 qubits, you would need 2^300 numbers, roughly the number of protons in the known universe, so no amount of Moore’s Law scaling will ever make it possible for a classical computer to process that many numbers,” said Nicholas Guise, a GTRI research scientist who led the research. “This is why it’s impossible to fully simulate even a modest sized quantum system, let alone something like chemistry of complex molecules, unless we can build a quantum computer to do it.”
While existing computers use classical bits of information, quantum computers use “quantum bits” or qubits to store information. Classical bits use either a 0 or 1, but a qubit, exploiting a weird quantum property called superposition, can actually be in both 0 and 1 simultaneously, allowing much more information to be encoded. Since qubits can be correlated with each other in a way that classical bits cannot, they allow a new sort of massively parallel computation, but only if many qubits at a time can be produced and controlled. The challenge that the field has faced is scaling this technology up, much like moving from the first transistors to the first computers.
One leading qubit candidate is individual ions trapped inside a vacuum chamber and manipulated with lasers. The scalability of current trap architectures is limited since the connections for the electrodes needed to generate the trapping fields come at the edge of the chip, and their number are therefore limited by the chip perimeter.
The GTRI/Honeywell approach uses new microfabrication techniques that allow more electrodes to fit onto the chip while preserving the laser access needed.
The team’s design borrows ideas from a type of packaging called a ball grid array (BGA) that is used to mount integrated circuits. The ball grid array’s key feature is that it can bring electrical signals directly from the backside of the mount to the surface, thus increasing the potential density of electrical connections.
The researchers also freed up more chip space by replacing area-intensive surface or edge capacitors with trench capacitors and strategically moving wire connections.
The space-saving moves allowed tight focusing of an addressing laser beam for fast operations on single qubits. Despite early difficulties bonding the chips, a solution was developed in collaboration with Honeywell, and the device was trapping ions from the very first day.
The team was excited with the results. “Ions are very sensitive to stray electric fields and other noise sources, and a few microns of the wrong material in the wrong place can ruin a trap. But when we ran the BGA trap through a series of benchmarking tests we were pleasantly surprised that it performed at least as well as all our previous traps,” Guise said.
Working with trapped ion qubits currently requires a room full of bulky equipment and several graduate students to make it all run properly, so the researchers say much work remains to be done to shrink the technology. The BGA project demonstrated that it’s possible to fit more and more electrodes on a surface trap chip while wiring them from the back of the chip in a compact and extensible way. However, there are a host of engineering challenges that still need to be addressed to turn this into a miniaturized, robust and nicely packaged system that would enable quantum computing, the researchers say.
In the meantime, these advances have applications beyond quantum computing. “We all hope that someday quantum computers will fulfill their vast promise, and this research gets us one step closer to that,” Guise said. “But another reason that we work on such difficult problems is that it forces us to come up with solutions that may be useful elsewhere. For example, microfabrication techniques like those demonstrated here for ion traps are also very relevant for making miniature atomic devices like sensors, magnetometers and chip-scale atomic clocks.”
13 May 2015
Photoacoustic imaging is a ground-breaking technique for spotting tumors inside living cells with the help of light-absorbing compounds known as contrast agents. A*STAR researchers have now discovered a way to improve the targeting efficacy and optical activity of breast-cancer-specific contrast agents using conjugated polymer nanoparticles.
Generating photoacoustic signals requires an ultrafast laser pulse to irradiate a small area of tissue. This sets off a series of molecular vibrations that produce ultrasonic sound waves in the sample. By ‘listening’ to the pressure differences created by the acoustic waves, researchers can reconstruct and visualize the inner structures of complex objects such as the brain and cardiovascular systems.
Diagnosing cancer with photoacoustic imaging requires contrast agents that deeply penetrate tissue and selectively bind to malignant cells. In addition, they need a high optical response to near-infrared laser light, a spectral region that is particularly safe to biological materials. Traditional contrast agents have been based on gold and silver nanostructures, but the complex chemical procedures needed to optically tune these nanocompounds have left researchers looking for alternatives.
Photoacoustic imaging of model breast cancer cells in mice reveals that a polymer-based contrast agent can illuminate tumor sites within one hour. Credit: Dove Medical Press Limited
Malini Olivo and her colleagues from the A*STAR Singapore Bioimaging Consortium and the A*STAR Institute of Materials Research and Engineering investigated different contrast agents based on conjugated polymers. These organic macromolecules, which contain alternating double and single carbon bonds, have delocalized electrons in their frameworks that can produce useful optical properties such as photoluminescence. The researchers identified a conjugated polymer known as PFTTQ—a compound with multiple aromatic rings, alkyl chains, sulfur and nitrogen atoms—as a promising in vivo photoacoustic agent because of its biocompatible structure and light absorption that peaks in the near-infrared range.
To direct this contrast agent to cancer cells, the team synthesized ‘dot’-like nanostructures with an inner core of PFTTQ surrounded by water-soluble polyethylene glycol chains, terminated by an outer layer of folate molecules—a vitamin that specifically binds to folate receptor proteins commonly expressed by breast cancer tumors. Experiments with MCF-7 model breast cancer cells implanted in mice revealed the merits of this approach: in just one hour after administering the folate–conjugated polymer dots, strong photoacoustic signals emerged from the tumor positions. The folate functionality played a critical role in this bioimaging procedure, quadrupling the photoacoustic signals compared to unmodified PFTTQ dots.
“The folate–PFTTQ nanoparticles have great potential for diagnostic imaging and other biomedical applications,” says Olivo. “We are working to expand the library of biocompatible polymers to use as molecular photoacoustic contrast agents.”
More information: “Molecular photoacoustic imaging of breast cancer using an actively targeted conjugated polymer.” International Journal of Nanomedicine 10, 387–397 (2015). dx.doi.org/10.2147/IJN.S73558
13 May 2015
Many of us are familiar with electrolytic splitting of water from their school days: If you hold two electrodes into an aqueous electrolyte and apply a sufficient voltage, gas bubbles of hydrogen and oxygen are formed. If this voltage is generated by sunlight in a solar cell, then you could store solar energy by generating hydrogen gas. This is because hydrogen is a versatile medium of storing and using “chemical energy”. Research teams all over the world are therefore working hard to develop compact, robust and cost-effective systems that can accomplish this challenge. But it is not that simple, because an efficient hydrogen generation preferably proceeds in an acidic electrolyte corroding very fast solar cells. Electrodes that so far have been used are made of very expensive elements such as platinum or platinum-iridium alloys.
New photocathode with several advantages
Under the “Light2Hydrogen” BMBF Cluster project and an on-going “Solar H2” DFG Priority program, a team from the HZB Institute for Solar Fuels has now developed a novel photoelectrode that solves these problems: It consists of chalcopyrite (a material used in device grade thin film solar cells) that has been coated with a thin, transparent, conductive oxide film of titanium dioxide (TiO2). The special characteristics are: The TiO2 film is polycrystalline and contains a small amount of platinum in the form of nanoparticles. This new composite presents some special talents. Firstly, it produces under sun light illumination a photovoltage of almost 0.5 V and very high photocurrent densities of up to 38 mA/cm2; secondly, it acts as a catalyst to accelerate the formation of hydrogen, and finally, it is chemically protected against corrosion as well. Since TiO2 is transparent, almost all sun light reaches the photoactive chalcopyrite, leading to the observed high photocurrent density and photovoltage comparable with those of a conventional device-grade thin-film solar cell.
HZB recipe and technology
The recipe for this novel and elegant coating was developed by Anahita Azarpira in the course of her doctoral studies in a team headed by Assoc. Prof. Thomas Schedel-Niedrig. She uses a chemical vapor coating technique (sprayed ion-layer gas reaction/Spray-ILGAR) that was developed and patented at the HZB Institute for Heterogeneous Material Systems (EE-IH). In this process, the titanium dioxide and platinum precursors are dissolved in ethanol and converted to a fog using an ultrasonic bath. The produced aerosol is directed over the heated substrate using a stream of nitrogen gas resulting into a polycrystalline thin film grown on the chalcopyrite substrate over time with embedded nanoparticles of platinum.
More than 80% of light converted
Azarpira and her colleagues varied the amount of platinum in the precursor solution in order to optimize the properties of the novel composite photoelectrode device. The properties were optimal with a volumetric proportion of about 5% platinum (H2PtCl6) in the precursor solution.”
More than 80% of the incident visible sunlight was photoelectrically converted by this composite system into electric current available for the hydrogen generation”, says Schedel-Niedrig. That means little light is lost and the quantum efficiency is virtually very high. In addition, it has been reported in the very recently published article that the composite shows high long-term stability over 25 hrs and reveals large photoelectrocatalytic activity of about 690 hydrogen molecules produced per second and per active center at the surface under illumination.
However, there is still a lot to do. Currently, the majority of the required voltage between the composite photocathode and a platinum counter electrode of around 1.8 V is still coming from a battery. Hence the solar-to-hydrogen efficiency has to be clearly improved. “But anyway, we demonstrate the feasibility of such future-oriented chemical robust photoelectrocatalytic systems that have the potential to convert solar energy to hydrogen, i.e to chemical energy for storage. As a consequence we have successfully developed and tested a demonstrator device for solar hydrogen production with a company in Schwerin under the Light2Hydrogen project, according to Schedel-Niedrig.
Ground-breaking research has successfully created the world’s first truly electronic textile, using the wonder material Graphene. An international team of scientists, including Professor Monica Craciun from the University of Exeter, have pioneered a new technique to embed transparent, flexible graphene electrodes into fibers commonly associated with the textile industry.
The international collaborative research, which includes experts from the Centre for Graphene Science at the University of Exeter, the Institute for Systems Engineering and Computers, Microsystems and Nanotechnology (INESC-MN) in Lisbon, the Universities of Lisbon and Aveiro in Portugal and the Belgian Textile Research Centre (CenTexBel), is published in the leading scientific journal Scientific Reports.
Professor Craciun, co-author of the research said: “This is a pivotal point in the future of wearable electronic devices. The potential has been there for a number of years, and transparent and flexible electrodes are already widely used in plastics and glass, for example. But this is the first example of a textile electrode being truly embedded in a yarn. The possibilities for its use are endless, including textile GPS systems, to biomedical monitoring, personal security or even communication tools for those who are sensory impaired. The only limits are really within our own imagination.”
At just one atom thick, graphene is the thinnest substance capable of conducting electricity. It is very flexible and is one of the strongest known materials. The race has been on for scientists and engineers to adapt graphene for the use in wearable electronic devices in recent years.
This new research has identified that ‘monolayer graphene’, which has exceptional electrical, mechanical and optical properties, make it a highly attractive proposition as a transparent electrode for applications in wearable electronics. In this work graphene was created by a growth method called chemical vapor deposition (CVD) onto copper foil, using a state-of-the-art nanoCVD system recently developed by Moorfield.
The collaborative team established a technique to transfer graphene from the copper foils to a polypropylene fibre already commonly used in the textile industry.
Dr Helena Alves who led the research team from INESC-MN and the University of Aveiro said: “The concept of wearable technology is emerging, but so far having fully textile-embedded transparent and flexible technology is currently non-existing. Therefore, the development of processes and engineering for the integration of graphene in textiles would give rise to a new universe of commercial applications. “
Dr Ana Neves, Associate Research Fellow in Prof Craciun’s team from Exeter’s Engineering Department and former postdoctoral researcher at INESC added: “We are surrounded by fabrics, the carpet floors in our homes or offices, the seats in our cars, and obviously all our garments and clothing accessories. The incorporation of electronic devices on fabrics would certainly be a game-changer in modern technology.
“All electronic devices need wiring, so the first issue to be address in this strategy is the development of conducting textile fibers while keeping the same aspect, comfort and lightness. The methodology that we have developed to prepare transparent and conductive textile fibers by coating them with graphene will now open way to the integration of electronic devices on these textile fibers.”
Dr Isabel De Schrijver,an expert of smart textiles fromCenTexBel said: “Successful manufacturing of wearable electronics has the potential for a disruptive technology with a wide array of potential new applications. We are very excited about the potential of this breakthrough and look forward to seeing where it can take the electronics industry in the future.”
Professor Saverio Russo, co-author and also from the University of Exeter, added: “This breakthrough will also nurture the birth of novel and transformative research directions benefitting a wide range of sectors ranging from defense to health care. “
In 2012 Professor Craciun and Professor Russo, from the University of Exeter’s Centre for Graphene Science, discovered GraphExeter – sandwiched molecules of ferric chloride between two graphene layers which makes a whole new system that is the best known transparent material able to conduct electricity. The same team recently discovered that GraphExeter is also more stable than many transparent conductors commonly used by, for example, the display industry.
Source: University of Exeter
09 May 2015
Water scarcity is a growing problem across the world. John H. Lienhard V and his team at MIT are exploring how to make renewable energy more efficient and affordable. Mechanical engineers and nanotechnologists are looking at different methods, including solar desalination.
It’s easier to dissolve a sugar cube in a glass of water by crushing the cube first, because the numerous tiny particles cover more surface area in the water than the cube itself. In a way, the same principle applies to the potential value of materials composed of nanoparticles.
Because nanoparticles are so small, millions of times smaller than the width of a human hair, they have “tremendous surface area,” raising the possibility of using them to design materials with more efficient solar-to-electricity and solar-to-chemical energy pathways, says Ari Chakraborty, an assistant professor of chemistry at Syracuse University.
“They are very promising materials,” he says. “You can optimize the amount of energy you produce from a nanoparticle-based solar cell.”
Ari Chakraborty is an assistant professor of chemistry at Syracuse University. Credit: Ari Chakraborty, Syracuse University >>>
Chakraborty, an expert in physical and theoretical chemistry, quantum mechanics and nanomaterials, is seeking to understand how these nanoparticles interact with light after changing their shape and size, which means, for example, they ultimately could provide enhanced photovoltaic and light-harvesting properties. Changing their shape and size is possible “without changing their chemical composition,” he says. “The same chemical compound in different sizes and shapes will interact differently with light.”
Specifically, the National Science Foundation (NSF)-funded scientist is focusing on quantum dots, which are semiconductor crystals on a nanometer scale. Quantum dots are so tiny that the electrons within them exist only in states with specific energies. As such, quantum dots behave similarly to atoms, and, like atoms, can achieve higher levels of energy when light stimulates them.
Chakraborty works in theoretical and computational chemistry, meaning “we work with computers and computers only,” he says. “The goal of computational chemistry is to use fundamental laws of physics to understand how matter interacts with each other, and, in my research, with light. We want to predict chemical processes before they actually happen in the lab, which tells us which direction to pursue.”
These atoms and molecules follow natural laws of motion, “and we know what they are,” he says. “Unfortunately, they are too complicated to be solved by hand or calculator when applied to chemical systems, which is why we use a computer.”
The “electronically excited” states of the nanoparticles influence their optical properties, he says.
“We investigate these excited states by solving the Schrödinger equation for the nanoparticles,” he says, referring to a partial differential equation that describes how the quantum state of some physical system changes with time. “The Schrödinger equation provides the quantum mechanical description of all the electrons in the nanoparticle.
“However, accurate solution of the Schrödinger equation is challenging because of large number of electrons in system,” he adds. “For example, a 20 nanometer CdSe quantum dot contains over 6 million electrons. Currently, the primary focus of my research group is to develop new quantum chemical methods to address these challenges. The newly developed methods are implemented in open-source computational software, which will be distributed to the general public free of charge.”
Solar voltaics, “requires a substance that captures light, uses it, and transfers that energy into electrical energy,” he says. With solar cell materials made of nanoparticles, “you can use different shapes and sizes, and capture more energy,” he adds. “Also, you can have a large surface area for a small amount of materials, so you don’t need a lot of them.”
Nanoparticles also could be useful in converting solar energy to chemical energy, he says. “How do you store the energy when the sun is not out?” he says. “For example, leaves on a tree take energy and store it as glucose, then later use the glucose for food. One potential application is to develop artificial leaves for artificial photosynthesis. There is a huge area of ongoing research to make compounds that can store energy.”
Medical imaging presents another useful potential application, he says.
“For example, nanoparticles have been coated with binding agents that bind to cancerous cells,” he says. “Under certain chemical and physical conditions, the nanoparticles can be tuned to emit light, which allows us to take pictures of the nanoparticles. You could pinpoint the areas where there are cancerous cells in the body. The regions where the cancerous cells are located show up as bright spots in the photograph.”
Chakraborty is conducting his research under an NSF Faculty Early Career Development (CAREER) award. The award supports junior faculty who exemplify the role of teacher-scholars through outstanding research, excellent education and the integration of education and research within the context of the mission of their organization. NSF is funding his work with $622,123 over five years.
As part of the grant’s educational component, Chakraborty is hosting several students from a local high school–East Syracuse Mineoa High School–in his lab. He also has organized two workshops for high school teachers on how to use computational tools in their classrooms “to make chemistry more interesting and intuitive to high school students,” he says.
“The really good part about it is that the kids can really work with the molecules because they can see them on the screen and manipulate them in 3-D space,” he adds. “They can explore their structure using computers. They can measure distances, angles, and energies associated with the molecules, which is not possible to do with a physical model. They can stretch it, and see it come back to its original structure. It’s a real hands-on experience that the kids can have while learning chemistry.”
Source: By Marlene Cimons, National Science Foundation
08 May 2015
Summary: Some substances, when they undergo a process called ‘rapid-freezing’ or ‘supercooling,’ remain in liquid form — even at below-freezing temperatures. A new study is the first to break down the rules governing the complex process of crystallization through rapid-cooling.
Its findings may revolutionize the delivery of drugs in the human body, providing a way to ‘freeze’ the drugs at an optimal time and location in the body.
Water, when cooled below 32°F, eventually freezes — it’s science known even to pre-schoolers. But some substances, when they undergo a process called “rapid-freezing” or “supercooling,” remain in liquid form — even at below-freezing temperatures.
The supercooling phenomenon has been studied for its possible applications in a wide spectrum of fields. A new Tel Aviv University study published in Scientific Reports is the first to break down the rules governing the complex process of crystallization through rapid-cooling. According to the research, membranes can be engineered to crystallize at a specific time. In other words, it is indeed possible to control what was once considered a wild and unpredictable process — and it may revolutionize the delivery of drugs in the human body, providing a way to “freeze” the drugs at the exact time and biological location in the body necessary.
The study was led jointly by Dr. Roy Beck of the Department of Physics at TAU’s School of Physics and Astronomy and Prof. Dan Peer of the Department of Cell Research and Immunology at TAU’s Faculty of Life Sciences, and conducted by TAU graduate students Guy Jacoby, Keren Cohen, and Kobi Barkai.
Controlling a metastable process
“We describe a supercooled material as ‘metastable,’ meaning it is very sensitive to any external perturbation that may transform it back to its stable low-temperature state,” Dr. Beck said. “We discovered in our study that it is possible to control the process and harness the advantages of the fluid/not-fluid transition to design a precise and effective nanoscale drug encapsulating system.”
For the purpose of the study, the researchers conducted experiments on nanoscale drug vesicles (fluid-filled sacs that deliver drugs to their targets) to determine the precise dynamics of crystallization. The researchers used a state-of-the-art X-ray scattering system sensitive to nanoscale structures.
“One key challenge in designing new nano-vesicles for drug delivery is their stability,” said Dr. Beck. “On the one hand, you need a stable vesicle that will entrap your drug until it reaches the specific diseased cell. But on the other, if the vesicle is too stable, the payload may not be released upon arrival at its target.”
“Supercooled material is a suitable candidate since the transition between liquid and crystal states is very drastic and the liquid membrane explodes to rearrange as crystals. Therefore this new physical insight can be used to release entrapped drugs at the target and not elsewhere in the body’s microenvironment. This is a novel mechanism for timely drug release.”
All in the timing
The researchers found that the membranes were able to remain stable for tens of hours before collectively crystallizing at a predetermined time.
“What was amazing was our ability to reproduce the results over and over again without any complicated techniques,” said Dr. Beck. “We showed that the delayed crystallization was not sensitive to minor imperfection or external perturbation. Moreover, we found multiple alternative ways to ‘tweak the clock’ and start the crystallization process.”
The researchers are investigating an appropriate new nano-capsule capable of releasing medication at a specific time and place in the body. “The challenge now is to find the right drugs to exploit our insights for the medical benefit of patients,” said Dr. Beck.
- Guy Jacoby, Keren Cohen, Kobi Barkan, Yeshayahu Talmon, Dan Peer, Roy Beck. Metastability in lipid based particles exhibits temporally deterministic and controllable behavior. Scientific Reports, 2015; 5: 9481 DOI: 10.1038/srep09481
The race to make the first quantum computer is becoming as important as the race 75 years ago to get the first nuke. It could change the balance of power in politics and business.
Quantum computers have long been theoretically possible but a kind of futuristic fantasy, like Interstellar-style wormhole travel, or zero-calorie Hershey Bars. I first wrote in the 1990s about the quest for one.
Now breakthroughs are coming faster, and scientists say we’re 15 to 20 years away from fully functional, programmable quantum computers.
This technology will make the microprocessor in your laptop seem as sophisticated as a booger. The silicon-based technology inside today’s computers, which engineers have constantly made faster and cheaper for five decades, is running out of ways to get better. Quantum computers will herald, well, a quantum leap—like riding a horse one day and getting into a fighter jet the next. These machines will be millions of times more powerful than today’s fastest supercomputers, solving problems that now elude solving, like dead-on accurate weather prediction or modeling protein molecules for medical research.
A quantum computer could also create indestructible encryption, and unlock any existing computer security as easily as you unzip your fly. We’re entering an era of cyberwar, so imagine how power might shift if one country gets the ability to invade any other country’s computer systems while putting up the ultimate computer defenses. That’s a major reason nations are pouring money into this research. The U.K., China, Russia, Australia, Netherlands and other countries are in the game. In the U.S., the CIA, National Security Agency and Pentagon are all funding research, while Los Alamos National Laboratory operates one of the most significant quantum computer labs.
Negotiations to keep nuclear weapons from Iran are certainly critical, but if you play out the promise of quantum computing, an American machine could bust into Iranian systems and shut down all that country’s nuclear activity in an instant. It’s like a game of rock-paper-scissors: Nukes might be the world’s version of a rock, but quantum computers would be paper, winning every time.
And yet, quantum computing research isn’t self-contained and secretive in the manner of the Los Alamos atomic bomb work during World War II. Some of it is academic work at universities such as the Massachusetts Institute of Technology, with findings shared in scientific papers. Technology companies are working on this, too, since these things have the potential to be business nukes. IBM, Google and Microsoft all fund research. Imagine if Google gets one before Microsoft. That pesky Bing could wind up vaporized. Google has a Quantum Artificial Intelligence unit working with the University of California, Santa Barbara, with a goal of developing a quantum machine that can learn.
Meanwhile, a Canadian startup, D-Wave Systems, is partially funded by Amazon CEO Jeff Bezos—and the CIA. The very secretive and often controversial company is already marketing a hybrid machine that seems to be a traditional silicon computer with some sort of quantum turbo thruster.
There’s no telling, yet, how this technology will emerge, or whether it will be hoarded by a few nations (like nukes) or spread around the globe (like computers). “There’s a healthy mix of cooperation and competition,” IBM quantum computing scientist Jerry Chow tells me. “But there’s starting to be more competition.”
Keep in mind that this technology is really hard, and really, really weird. A quantum computer makes calculations using the spin of special atoms, called qubits, and it relies on bizarre quantum physics properties like multiple parallel universes. Quantum computing is so fast because it calculates all possible answers at the same time. To borrow a metaphor from D-Wave CEO Vern Brownell, let’s say you had to find an X written on one page among the 37 million books in the Library of Congress. A typical computer today would look at every page, one at a time—very quickly, but still in a serial process. A quantum computer could look at every page at the same time—as if it were splitting the task into a billion parallel universes, finding the answer, then coming back to ours to show us where that X is.
Scientists have managed to get a few qubits to do calculations in labs, but we are far from getting a stable, programmable, fully quantum machine. On April 29, IBM announced what it says is a significant advance—a way to detect and measure the two types of quantum errors, called bit-flip and phase-flip, at the same time. That sounds esoteric to most of us, but it will help with a peculiar problem that vexes researchers: The very act of looking at a qubit to get its answer can make the qubit change its answer. So some mechanism needs to figure out whether we’re seeing the right answer. Again—this stuff is really weird.
The various labs often disagree on the best way to build a quantum computer, and the art of programming qubits is as big a challenge as making the machine in the first place. Today’s software is based on algorithms, which are linear, one-step-at-a-time calculations. Top mathematicians aren’t yet sure how to write algorithms that calculate everything at the same time. It’s like trying to come up with a recipe for an apple pie in which all the ingredients combine in the pan in the same split second.
Yet hard as this work seems, scientists have become sure that the first quantum computers are within reach. Expect quantum computing news to keep coming. And it might not be too early to prepare for quantum-era life a couple decades from now. If you’re already worried that artificial intelligence will take your job, quantum AI will seem terrifying. Your Google self-driving car will be smarter than your whole department.
Summary: For faster, longer-lasting water filters, some scientists are looking to graphene –thin, strong sheets of carbon — to serve as ultrathin membranes, filtering out contaminants to quickly purify high volumes of water.
Graphene’s unique properties make it a potentially ideal membrane for water filtration or desalination. But there’s been one main drawback to its wider use: Making membranes in one-atom-thick layers of graphene is a meticulous process that can tear the thin material — creating defects through which contaminants can leak. Now engineers have devised a process to repair these leaks.
Graphene’s unique properties make it a potentially ideal membrane for water filtration or desalination. But there’s been one main drawback to its wider use: Making membranes in one-atom-thick layers of graphene is a meticulous process that can tear the thin material — creating defects through which contaminants can leak.
Now engineers at MIT, Oak Ridge National Laboratory, and King Fahd University of Petroleum and Minerals (KFUPM) have devised a process to repair these leaks, filling cracks and plugging holes using a combination of chemical deposition and polymerization techniques. The team then used a process it developed previously to create tiny, uniform pores in the material, small enough to allow only water to pass through.
Combining these two techniques, the researchers were able to engineer a relatively large defect-free graphene membrane — about the size of a penny. The membrane’s size is significant: To be exploited as a filtration membrane, graphene would have to be manufactured at a scale of centimeters, or larger.
In experiments, the researchers pumped water through a graphene membrane treated with both defect-sealing and pore-producing processes, and found that water flowed through at rates comparable to current desalination membranes. The graphene was able to filter out most large-molecule contaminants, such as magnesium sulfate and dextran.
Rohit Karnik, an associate professor of mechanical engineering at MIT, says the group’s results, published in the journal Nano Letters, represent the first success in plugging graphene’s leaks.
“We’ve been able to seal defects, at least on the lab scale, to realize molecular filtration across a macroscopic area of graphene, which has not been possible before,” Karnik says. “If we have better process control, maybe in the future we don’t even need defect sealing. But I think it’s very unlikely that we’ll ever have perfect graphene — there will always be some need to control leakages. These two [techniques] are examples which enable filtration.”
Sean O’Hern, a former graduate research assistant at MIT, is the paper’s first author. Other contributors include MIT graduate student Doojoon Jang, former graduate student Suman Bose, and Professor Jing Kong.
A delicate transfer
“The current types of membranes that can produce freshwater from saltwater are fairly thick, on the order of 200 nanometers,” O’Hern says. “The benefit of a graphene membrane is, instead of being hundreds of nanometers thick, we’re on the order of three angstroms — 600 times thinner than existing membranes. This enables you to have a higher flow rate over the same area.”
O’Hern and Karnik have been investigating graphene’s potential as a filtration membrane for the past several years. In 2009, the group began fabricating membranes from graphene grown on copper — a metal that supports the growth of graphene across relatively large areas. However, copper is impermeable, requiring the group to transfer the graphene to a porous substrate following fabrication.
However, O’Hern noticed that this transfer process would create tears in graphene. What’s more, he observed intrinsic defects created during the growth process, resulting perhaps from impurities in the original material.
Plugging graphene’s leaks
To plug graphene’s leaks, the team came up with a technique to first tackle the smaller intrinsic defects, then the larger transfer-induced defects. For the intrinsic defects, the researchers used a process called “atomic layer deposition,” placing the graphene membrane in a vacuum chamber, then pulsing in a hafnium-containing chemical that does not normally interact with graphene. However, if the chemical comes in contact with a small opening in graphene, it will tend to stick to that opening, attracted by the area’s higher surface energy.
The team applied several rounds of atomic layer deposition, finding that the deposited hafnium oxide successfully filled in graphene’s nanometer-scale intrinsic defects. However, O’Hern realized that using the same process to fill in much larger holes and tears — on the order of hundreds of nanometers — would require too much time.
Instead, he and his colleagues came up with a second technique to fill in larger defects, using a process called “interfacial polymerization” that is often employed in membrane synthesis. After they filled in graphene’s intrinsic defects, the researchers submerged the membrane at the interface of two solutions: a water bath and an organic solvent that, like oil, does not mix with water.
In the two solutions, the researchers dissolved two different molecules that can react to form nylon. Once O’Hern placed the graphene membrane at the interface of the two solutions, he observed that nylon plugs formed only in tears and holes — regions where the two molecules could come in contact because of tears in the otherwise impermeable graphene — effectively sealing the remaining defects.
Using a technique they developed last year, the researchers then etched tiny, uniform holes in graphene — small enough to let water molecules through, but not larger contaminants. In experiments, the group tested the membrane with water containing several different molecules, including salt, and found that the membrane rejected up to 90 percent of larger molecules. However, it let salt through at a faster rate than water.
The preliminary tests suggest that graphene may be a viable alternative to existing filtration membranes, although Karnik says techniques to seal its defects and control its permeability will need further improvements.
“Water desalination and nanofiltration are big applications where, if things work out and this technology withstands the different demands of real-world tests, it would have a large impact,” Karnik says. “But one could also imagine applications for fine chemical- or biological-sample processing, where these membranes could be useful. And this is the first report of a centimeter-scale graphene membrane that does any kind of molecular filtration. That’s exciting.”
- Sean C. O’Hern, Doojoon Jang, Suman Bose, Juan-Carlos Idrobo, Yi Song, Tahar Laoui, Jing Kong, Rohit Karnik. Nanofiltration across Defect-Sealed Nanoporous Monolayer Graphene. Nano Letters, 2015; 150427124208006 DOI: 10.1021/acs.nanolett.5b00456
08 May 2015
But because the blood containing the drug travels all round your body only a small percentage of the initial dose actually reaches the desired location.
For over-the-counter drugs like paracetamol or ibuprofen, with very few side-effects, this doesn’t matter too much.
But when it comes to cancer drugs, which can affect healthy cells just as much as cancer cells, this process can cause big problems.
Partly because drugs are diluted in their blood, cancer patients need to take these drugs in particularly high doses – and this can cause seriously unpleasant side effects.
But Professor Sonia Trigueros, co-director of the Oxford Martin Programme on Nanotechnology, is inching closer to developing a nano-scale drug delivery system with the aim of specifically targeting cancer cells.
Working with a team of chemists, engineers and physicists, Trigueros has embarked on an ambitious mission to tackle cancer at the ‘nano’ level – less than 100 nanometers wide. For context, this is super-tiny: a nanometre is a thousandth of a thousandth of a millimetre.
There’s still a long way to go, but Trigueros is making decent headway, and has recently tackled a major problem of working at a nano level. And at this year’s Wired Health conference – which looked at the future of health care, wellbeing and genomics – she told us about her recent progress, and her visions for the future.
At the nano level
Some of us will remember the periodic table displayed in our science classrooms which told us about the properties of each element. But working on a nano level everything changes, and elements behave completely differently.
Elements have different properties at the nano level than they do at the micro level, explained Prof Trigueros to the Wired Health 2015 audience.
This poses big problems for researchers trying to make nano-scale devices, which can be made out of a number of different materials, including gold, silver and carbon. All these materials are highly unstable at the nano level.
“After you make the nanostructures you only have minutes to a couple of days to work,” she said. They are really unstable, especially when you put them in water.”
This isn’t ideal, considering our bodies are made up mostly of water.
Trigueros’ recent work has focused on trying to stabilise tiny tubes made of carbon, called carbon nanotubes, which hold drugs inside the tube so they can be delivered into cancer cells.
She has now found a way of keeping them stable for more than two years and in temperatures up to 42ºC.
To do this, she wraps DNA around the structures, like a tortilla wraps around the fillings of a burrito.
While this accomplishes the goal of keeping the nanostructures stable inside the body this doesn’t do much good if the DNA can’t unwrap to deliver the drugs. But, according to Trigueros, she has shown that, once inside a cell, the DNA easily unwinds and releases its payload.
Truly targeted drug delivery
So how does it all work? How do the drugs get into the cancer cells? Trigueros’s nanotubes exploit the differences between cancer cells and healthy cells – in this case, differences in the membranes that hold them together.
“Cancer cells are more permeable than normal cells so the nanotubes can get through the cell membrane. And once they are in, they unwrap and deliver drug,” explained Trigueros.
Exploiting differences in their permeability is one way to target the cancer cells, but Trigueros explains that there is more than one way to create a truly targeted drug delivery system.
“We can attach whatever we want on DNA,” she said. “So you can attach a protein that recognises cancer cells”.
From theory to reality
While this all sounds great in theory, will it actually work in reality?
Trigueros has now started preliminary tests on laboratory grown lung cancer cells, she told us during an interview. And this has shown tentative promise, she says, citing unpublished data on their effectiveness at killing these cells in the lab.
Others are cautiously optimistic. “This is a really exciting prospect,” says Professor Duncan Graham, nanotechnology expert and advisor to Cancer Research UK.
“A common concern with carbon nanotubes is toxicity, but when coated with DNA this concern could be removed,” he explains, “and it also addresses a fundamental issue, which is that they collect into clusters that become a solid mass and so are unable to leave the body.”
In theory, once Trigueros’s nanotubes have finished their job they are tiny enough (50 nanometres) to be excreted through urine.
This isn’t the first time carbon nanotubes have been used in cancer research: a US research team has used them, for example, to target and collect images of tumours in mice. But the combination of drug delivery and cancer-specific targeting is what interests Professor Graham.
“Unlike previous work using carbon nanotubes, this approach is set to target the tumour specifically, potentially meaning fewer side effects and a lower dosage. I look forward to seeing this in animal models which is where the real proof of activity lies,” he said.
But he’s cautious, stressing that Trigueros’s work has not yet been peer-reviewed and published.
Next Trigueros is aiming towards starting animal trials and, eventually, she wants to begin clinical trials in patients – that is if everything goes well.
She hopes to focus on how nanostructures could be used to cross the blood-brain barrier – the brain’s highly selective ‘bouncer’ that only lets certain molecules across. This has been notoriously difficult to get past, making targeting cancers in the brain more difficult.
But there is a still a long way to go and a lot of problems to tackle. In the shorter term, we’ll be keeping an eager eye on her drug delivery research, as her ideas continue to develop.
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