Kong X.,Nankai University |
Huang Y.,Center for Nanoscale Science and Technology
Journal of Nanoscience and Nanotechnology | Year: 2014
This paper reviews the up-to-date research about the applications of graphene and its related materials in the field of mass spectrometry (MS). Due to its large surface area, delocalized π-electrons, thermal conductivity, stability and rich interaction chemistry, graphene has been widely used in MS-based analytical chemistry. Graphene-based materials were applied as very effective matrixes or surfaces for many kinds of organic molecules in laser desorption/ionization (LDI) MS analysis. Many advantages of this novel matrix have been proved, which included: low interference ions from matrix itself, good reproducibility, high salt tolerance and so on. The unique properties of graphene also make it a superior sorbent used in solid-phase extraction (SPE). Further development of online SPE methods based on graphene coupling directly with LDI-MS, GC-MS and LC-MS greatly simplifies the MS-based analytical procedure for complex samples and makes the corresponding high-throughput and automatic analysis performable. Their applications as a platform in proteolysis for the rapid identification of proteins have been also developed. In addition, graphene was found to be a unique precursor for the generation of large-sized carbon cluster anions in the gas phase. Finally, the possible challenges and future perspectives in their applications in MS are discussed too. Copyright © 2014 American Scientific Publishers All rights reserved.
The team's work, published in Nature Photonics, also was presented at the March 2016 meeting of the American Physical Society in Baltimore, Md. While Moore's Law, the idea that the number of transistors on an integrated circuit will double every two years, has proven remarkably resilient, engineers will soon begin to encounter fundamental limits. As transistors shrink, heat and other factors will begin to have magnified effects in circuits. As a result, researchers are increasingly considering designs in which electronic components interface with other physical systems that carry information such as light and sound. Interfacing these different types of physical systems could circumvent some of the problems of components that rely on just one type of information carrier, if researchers can develop efficient ways of converting signals from one type to another (transduction). For example, light is able to carry a lot of information and typically doesn't interact with its environment very strongly, so it doesn't heat up components like electricity does. As useful as light is, however, it isn't suited to every situation. Light is difficult to store for long periods, and it can't interact directly with some components of a circuit. On the other hand, acoustic wave devices are already used in wireless communications technology, where sound is easier to store for long periods in compact structures since it moves much more slowly. To address such needs, NIST researchers and their collaborators built a piezoelectric optomechanical circuit on a chip. At the heart of this circuit is an optomechanical cavity, which in their case consists of a suspended nanoscale beam. Within the beam are a series of holes that act sort of like a hall of mirrors for light (photons). Photons of a very specific color or frequency bounce back and forth between these mirrors thousands of times before leaking out. At the same time, the nanoscale beam confines phonons, that is, mechanical vibrations, at a frequency of billions of cycles per second (gigahertz or GHz). The photons and phonons exchange energy so that vibrations of the beam influence the buildup of photons inside the cavity, while the buildup of photons inside the cavity influences the size of the mechanical vibrations. The strength of this mutual interaction, or coupling, is one of the largest reported for an optomechanical system. One of the researchers' main innovations came from joining these cavities with acoustic waveguides, which are components that route sound waves to specific locations. By channeling phonons into the optomechanical device, the group was able to manipulate the motion of the nanoscale beam directly. Because of the energy exchange, the phonons could change the properties of the light trapped in the device. To generate the sound waves, which were at GHz frequencies (much higher than audible sounds; not even your dog could hear them), they used piezoelectric materials, which deform when an electric field is applied to them and vice versa. By using a structure known as an "interdigitated transducer" (IDT), which enhances this piezoelectric effect, the group was able to establish a link between radio frequency electromagnetic waves and the acoustic waves. The strong optomechanical links enable them to optically detect this confined coherent acoustic energy down to the level of a fraction of a phonon. They also observed controllable interference effects in sound waves by pitting electrically and optically generated phonons against each other. According to one of the paper's co-authors, Kartik Srinivasan, the device might allow detailed studies of these interactions and the development of phononic circuitry that can be modified with photons. "Future information processing systems may need to incorporate other information carriers, such as photons and phonons, in order to carry out different tasks in an optimal way," says Srinivasan, a physicist at NIST's Center for Nanoscale Science and Technology. "This work presents one platform for transducing information between such different carriers." Explore further: An optomechanical crystal to study interactions among colocalized photons and phonons
Abstract: When lots of energy hits an atom, it can knock off electrons, making the atom extremely chemically reactive and initiating further destruction. That's why radiation is so dangerous. It's also why high-resolution imaging techniques that use energetic electron beams and X-rays can alter, even obliterate, the samples they explore. For example, monitoring battery dynamics using electron microscopy can introduce artifacts that interfere with electrochemical processes. Another case in point: Employing X-ray spectroscopy to see inside a living cell annihilates that cell. Now, researchers at the Department of Energy's Oak Ridge National Laboratory and the National Institute of Standards and Technology have demonstrated a nondestructive way to observe nanoscale objects and processes in conditions simulating their normal operating environments. They start with an "environmental chamber" to encapsulate a sample in a liquid. The chamber has a window made of an ultrathin membrane (8 to 50 billionths of a meter, or nanometers, thick). The tip of a scanning probe microscope moves across the membrane, injecting microwaves into the chamber. The device records where the microwave signal was transmitted versus impeded and creates a high-resolution map of the sample. Because the injected microwaves are 100 million times weaker than those of a home microwave oven, and they oscillate in opposite directions several billions of times each second so potentially destructive chemical reactions cannot proceed, the ORNL-NIST technique produces only negligible heat and does not destroy the sample. The scientists report their novel approach of combining ultrathin membranes with microwaves and a scanning probe--called scanning microwave impedance microscopy, or sMIM--in the journal ACS Nano. "Our imaging is nondestructive and free from the damage frequently caused to samples, such a living cells or electrochemical processes, by imaging with X-ray or electron beams," said first author Alexander Tselev. With colleagues Anton Ievlev and Sergei Kalinin at the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility at ORNL, he performed high-resolution microwave imaging and analysis. "Its spatial resolution is better than what is achievable with optical microscopes for similar in-liquid samples. The paradigm can become instrumental for gaining important insights into electrochemical phenomena, living objects and other nanoscale systems existing in fluids." For example, microwave microscopy may provide a noninvasive way to explore important surface phenomena occurring on the scale of billionths of a meter, such as the formation of a thin coating that protects and stabilizes a new battery's electrode but cannibalizes its electrolyte to make the coating. Microwave microscopy, which allows scientists to watch processes as they're happening without stopping them cold, makes it possible to characterize ongoing chemical reactions at different stages. "At NIST, we developed environmental chambers with ultra-thin membranes to perform electron microscopy and other analytical techniques in liquids," said senior author Andrei Kolmakov. He and colleague Jeyavel Velmurugan at NIST's Center for Nanoscale Science and Technology made chambers to enclose objects and processes in liquid environments and performed preliminary characterizations to identify biologically interesting cells. "Conversations between the ORNL and NIST scientists resulted in the idea to try nondestructive microwaves so the environmental chambers could be used for broader studies. There are very few groups in the world that can image with high resolution using microwaves, and CNMS is among them. The design of the experiment and the adjustment of the technology for imaging required ORNL expertise." The ORNL and NIST researchers combined existing technologies in new ways and came up with a unique approach that may prove useful in medical diagnostics, forensics and materials research. "For the first time, we are able to image through a very thin membrane," Tselev said. "Microwaves and scanning probe microscopy allowed that." The right tool for the job To image highly ordered materials, such as crystals, researchers can employ techniques such as neutron scattering and X-ray diffraction. To image less ordered materials, such as living cell membranes, or processes, such as ongoing chemical reactions, the ORNL-NIST team collaborated closely to innovate the right tool for the job. Once the scientists had combined the environmental chamber with a scanning microwave capability, they investigated a model system to see if their new technique would work and to set a baseline for future experiments. They used the sMIM system to map polystyrene particles self-assembling into densely packed structures in a liquid. With that proof-of-principle achieved, they then asked if their system could discriminate between silver, which is an electrical conductor, and silver oxide, an insulator, during electroplating (an electrically induced reaction to deposit silver onto a surface). Optical microscopy and scanning electron microscopy are not good at distinguishing silver from silver oxide. Microwave microscopy, in contrast, unambiguously distinguished insulators from conductors. Next, the researchers needed to know that observation with sMIM would not introduce artifacts, such as silver precipitation, that scanning electron microscopy may cause--a problem that is not trivial. "One paper lists 79 chemical reactions induced by electrons in water," Tselev noted. Generally, scanning electron microscopy will not allow scientists to follow silver precipitation to form growing dendrites because that technique is destructive. "Dendrites behave very badly under an electron beam," Tselev said. With sMIM, electrochemical artifacts and process stoppage did not occur. "Whereas sMIM is not the only nondestructive technique, in many cases it may be the only one which can be used." Next the researchers imaged living cells. Because healthy and sick cells differ in properties such as the ability to store electrical energy, intracellular mapping could provide a basis for diagnosis. "Tomographic imaging--resolution across the depths--is possible with microwaves as well," Tselev said. "If you have microwaves, you can go variably in depth and get a lot of information about the living biological cell membrane itself--shape and properties that depend very much on the chemical composition and water content, which in turn depend on whether the cell is healthy or not." The researchers were able to detect properties distinguishing healthy from sick cells. In the current experiments, the system allowed observation close to surfaces. "That doesn't mean we'll not be able to see deeper if we redesign the experiment," Tselev said. "Microwaves can penetrate very deeply. The depth is basically limited by the contact size between the probe and the environmental cell membrane." Next the researchers will try to improve the sensitivity and spatial resolution of their system. Because thinning the walls of the environmental chamber would improve the resolution, the researchers will try making the walls with graphene or hexagonal boron nitride, both of which are only one atom thick. They will also use different probes and image-processing algorithms to improve resolution at different depths. The title of the paper is "Seeing Through Walls at the Nanoscale: Microwave Microscopy of Enclosed Objects and Processes in Liquids." The researchers conducted experiments at the CNMS, a DOE Office of Science User Facility at ORNL, and the Center for Nanoscale Science and Technology at NIST. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
News Article | April 13, 2016
What if doctors could deliver anti-cancer drugs directly to tumors without making patients sick? Bringing this dream of targeted drug delivery closer to reality for pharmaceutical manufacturers, researchers at the National Institute of Standards and Technology (NIST) have received a patent for a method to create precisely sized nanometer-scale capsules. The NIST method employs microfluidics to create precise nanoscale spherical capsules. Made of lipids, the kinds of biomolecules that also comprise fats, the spherical capsules are known as liposomes. Essentially, liposomes are simplified artificial versions of cell membranes, the outer coverings of cells. The inside of a liposome could hold drugs, and the outside could be coated with receptors that bind to specific cancer cells. The method can produce liposomes with typical diameters of 100-400 nanometers, or billionths of a meter. This size range is useful for attaching to cells, whose size is typically 1 to 10 micrometers, or millionths of a meter. Typical methods for making liposomes include pushing a lipid solution through a filter, a process that can lead to wide variations in the size of the resulting liposomes. Furthermore, the methods can be wasteful, and can result in large amounts of expensive drugs not being captured inside the liposomes and being discarded. In the NIST technique, lipid material is dissolved in isopropyl alcohol. The resulting lipid-containing solution is then forced into a narrow channel and further constricted when it is squeezed by streams of water coming at it from multiple sides. Lipid molecules are repelled by water, so they clump together and coalesce into spherical liposomes. Adjusting the flow rate of the water can control the size of the liposomes that form. “We have precision control over making liposomes and changing their size by dialing in flow rates,” says Michael Gaitan, who works in NIST’s Physical Measurement Laboratory. Researchers could dissolve drugs or other molecules of interest into the water stream, Gaitan explains. Adjusting the concentrations of these molecules can determine the amount of the drug that ends up in the liposome, down to the single-molecule level. This method, which has received interest in being licensed by companies, originally developed from basic research. Gaitan and collaborator Laurie Locascio were looking for ways to enclose individual molecules of interest in fluid-filled capsules to study their behavior in a liquid environment. Previous methods had anchored individual molecules in glass slides, which are rather unnatural environments, as opposed to the more cell-like environment of a fluid-filled liposome. Once this technique was developed, researchers were able to create a variety of liposomes of many useful sizes, and the potential drug-delivery applications became clear. The researchers were awarded a patent for this work late last year. "This research and the resulting patent also have implications for the on-demand formulation of drugs in a way that’s applicable to personalized or precision medicine," says Laurie Locascio, director of NIST’s Material Measurement Laboratory. “The reason that this patent is so fundamental is that this is a process patent,” which is a more general form of patent, Gaitan explains. The method does not require a specific experimental configuration, but is a general approach that can be realized in many ways, he says. Moving forward, researchers at NIST’s Center for Nanoscale Science and Technology are continuing to develop this technique for more applications by creating capsules made of different types of nanoparticles. Size — and control — most definitely matter in nanotechnology. Being able to create precisely sized nanocontainers can open up many new applications, Gaitan says.
Abstract: Converting a single photon from one color, or frequency, to another is an essential tool in quantum communication, which harnesses the subtle correlations between the subatomic properties of photons (particles of light) to securely store and transmit information. Scientists at the National Institute of Standards and Technology (NIST) have now developed a miniaturized version of a frequency converter, using technology similar to that used to make computer chips. The tiny device, which promises to help improve the security and increase the distance over which next-generation quantum communication systems operate, can be tailored for a wide variety of uses, enables easy integration with other information-processing elements and can be mass produced. The new nanoscale optical frequency converter efficiently converts photons from one frequency to the other while consuming only a small amount of power and adding a very low level of noise, namely background light not associated with the incoming signal. Frequency converters are essential for addressing two problems. The frequencies at which quantum systems optimally generate and store information are typically much higher than the frequencies required to transmit that information over kilometer-scale distances in optical fibers. Converting the photons between these frequencies requires a shift of hundreds of terahertz (one terahertz is a trillion wave cycles per second). A much smaller, but still critical, frequency mismatch arises when two quantum systems that are intended to be identical have small variations in shape and composition. These variations cause the systems to generate photons that differ slightly in frequency instead of being exact replicas, which the quantum communication network may require. The new photon frequency converter, an example of nanophotonic engineering, addresses both issues, Qing Li, Marcelo Davanço and Kartik Srinivasan write in Nature Photonics. The key component of the chip-integrated device is a tiny ring-shaped resonator, about 80 micrometers in diameter (slightly less than the width of a human hair) and a few tenths of a micrometer in thickness. The shape and dimensions of the ring, which is made of silicon nitride, are chosen to enhance the inherent properties of the material in converting light from one frequency to another. The ring resonator is driven by two pump lasers, each operating at a separate frequency. In a scheme known as four-wave-mixing Bragg scattering, a photon entering the ring is shifted in frequency by an amount equal to the difference in frequencies of the two pump lasers. Like cycling around a racetrack, incoming light circulates around the resonator hundreds of times before exiting, greatly enhancing the device's ability to shift the photon's frequency at low power and with low background noise. Rather than using a few watts of power, as typical in previous experiments, the system consumes only about a hundredth of that amount. Importantly, the added amount of noise is low enough for future experiments using single-photon sources. While other technologies have been applied to frequency conversion, "nanophotonics has the benefit of potentially enabling the devices to be much smaller, easier to customize, lower power, and compatible with batch fabrication technology," said Srinivasan. "Our work is a first demonstration of a nanophotonic technology suitable for this demanding task of quantum frequency conversion." ### This work was performed by researchers at NIST's Center for Nanoscale Science and Technology. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.