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    • 2019-01-03 09:05:38
    • Article ID: 705950

    Carrying and Releasing Nanoscale Cargo with "Nanowrappers"

    Nanocubes with hollow interiors and surface openings whose shape, size, and location are precisely controlled could be used to load and unload materials for biomedical, catalysis, and optical sensing applications

    • Credit: Brookhaven National Laboratory

      Yugang Zhang, Oleg Gang, Fang Lu, and Mingzhao Liu hold structural models of "nanowrappers" made of gold and silver and featuring holes in the corners. The scientists synthesized these hollow, porous nanostructures through a chemical reaction and characterized them using electron microscopy and optical spectroscopy capabilities at Brookhaven Lab's Center for Functional Nanomaterials.

    • The 3-D structure and chemical composition characterizations of the products obtained after five minutes (a), 20 minutes (b), and one hour (c). The scanning electron microscope images (subscript 1, scale bars are 100 nanometers), reconstructed 3-D volume renderings (subscript 2), and 3-D elemental mappings (subscript 3, gold in green and silver in red) show the transformation of the silver nanocubes into gold-silver nanowrappers.

    • Schematic for using the nanowrapper as a carrier to load and release a DNA-capped spherical nanoparticle. The blue and red on the direction arrow bars refer to low and high salt concentrations, respectively.

    UPTON, NY—This holiday season, scientists at the Center for Functional Nanomaterials (CFN)—a U.S. Department of Energy Office of Science User Facility at Brookhaven National Laboratory—have wrapped a box of a different kind. Using a one-step chemical synthesis method, they engineered hollow metallic nanosized boxes with cube-shaped pores at the corners and demonstrated how these “nanowrappers” can be used to carry and release DNA-coated nanoparticles in a controlled way. The research is reported in a paper published on Dec. 12 in ACS Central Science, a journal of the American Chemical Society (ACS).  

    “Imagine you have a box but you can only use the outside and not the inside,” said co-author Oleg Gang, leader of the CFN Soft and Bio Nanomaterials Group. “This is how we’ve been dealing with nanoparticles. Most nanoparticle assembly or synthesis methods produce solid nanostructures. We need methods to engineer the internal space of these structures.”

    “Compared to their solid counterparts, hollow nanostructures have different optical and chemical properties that we would like to use for biomedical, sensing, and catalytic applications,” added corresponding author Fang Lu, a scientist in Gang’s group. “In addition, we can introduce surface openings in the hollow structures where materials such as drugs, biological molecules, and even nanoparticles can enter and exit, depending on the surrounding environment.”

    Synthetic strategies have been developed to produce hollow nanostructures with surface pores, but typically the size, shape, and location of these pores cannot be well-controlled. The pores are randomly distributed across the surface, resulting in a Swiss-cheese-like structure. A high level of control over surface openings is needed in order to use nanostructures in practical applications—for example, to load and release nanocargo.

    In this study, the scientists demonstrated a new pathway for chemically sculpturing gold-silver alloy nanowrappers with cube-shaped corner holes from solid nanocube particles. They used a chemical reaction known as nanoscale galvanic replacement. During this reaction, the atoms in a silver nanocube get replaced by gold ions in an aqueous solution at room temperature. The scientists added a molecule (surfactant, or surface-capping agent) to the solution to direct the leaching of silver and the deposition of gold on specific crystalline facets.  

    “The atoms on the faces of the cube are arranged differently from those in the corners, and thus different atomic planes are exposed, so the galvanic reaction may not proceed the same way in both areas,” explained Lu. “The surfactant we chose binds to the silver surface just enough—not too strongly or weakly—so that gold and silver can interact. Additionally, the absorption of surfactant is relatively weak on the silver cube’s corners, so the reaction is most active here. The silver gets “eaten” away from its edges, resulting in the formation of corner holes, while gold gets deposited on the rest of the surface to create a gold and silver shell.”

    To capture the structural and chemical composition changes of the overall structure at the nanoscale in 3-D and at the atomic level in 2-D as the reaction proceeded over three hours, the scientists used electron microscopes at the CFN. The 2-D electron microscope images with energy-dispersive X-ray spectroscopy (EDX) elemental mapping confirmed that the cubes are hollow and composed of a gold-silver alloy. The 3-D images they obtained through electron tomography revealed that these hollow cubes feature large cube-shaped holes at the corners.

    “In electron tomography, 2-D images collected at different angles are combined to reconstruct an image of an object in 3-D,” said Gang. “The technique is similar to a CT [computerized tomography] scan used to image internal body structures, but it is carried out on a much smaller size scale and uses electrons instead of x-rays.”

    The scientists also confirmed the transformation of nanocubes to nanowrappers through spectroscopy experiments capturing optical changes. The spectra showed that the optical absorption of the nanowrappers can be tuned depending on the reaction time.  At their final state, the nanowrappers absorb infrared light.

    “The absorption spectrum showed a peak at 1250 nanometers, one of the longest wavelengths reported for nanoscale gold or silver,” said Gang. “Typically, gold and silver nanostructures absorb visible light. However, for various applications, we would like those particles to absorb infrared light—for example, in biomedical applications such as phototherapy.”

    Using the synthesized nanowrappers, the scientists then demonstrated how spherical gold nanoparticles of an appropriate size that are capped with DNA could be loaded into and released from the corner openings by changing the concentration of salt in the solution. DNA is negatively charged (owing to the oxygen atoms in its phosphate backbone) and changes its configuration in response to increasing or decreasing concentrations of a positively charged ion such as salt. In high salt concentrations, DNA chains contract because their repulsion is reduced by the salt ions. In low salt concentrations, DNA chains stretch because their repulsive forces push them apart.

    When the DNA strands contract, the nanoparticles become small enough to fit in the openings and enter the hollow cavity. The nanoparticles can then be locked within the nanowrapper by decreasing the salt concentration. At this lower concentration, the DNA strands stretch, thereby making the nanoparticles too large to go through the pores. The nanoparticles can leave the structure through a reverse process of increasing and decreasing the salt concentration.

    “Our electron microscopy and optical spectroscopy studies confirmed that the nanowrappers can be used to load and release nanoscale components,” said Lu. “In principle, they could be used to release optically or chemically active nanoparticles in particular environments, potentially by changing other parameters such as pH or temperature.”  

    Going forward, the scientists are interested in assembling the nanowrappers into larger-scale architectures, extending their method to other bimetallic systems, and comparing the internal and external catalytic activity of the nanowrappers.   

    “We did not expect to see such regular, well-defined holes,” said Gang. “Usually, this level of control is quite difficult to achieve for nanoscale objects. Thus, our discovery of this new pathway of nanoscale structure formation is very exciting. The ability to engineer nano-objects with a high level of control is important not only to understanding why certain processes are happening but also to constructing targeted nanostructures for various applications, from nanomedicine and optics to smart materials and catalysis. Our new synthesis method opens up unique opportunities in these areas.”  

    “This work was made possible by the world-class expertise in nanomaterial synthesis and capabilities that exist at the CFN,” said CFN Director Charles Black. “In particular, the CFN has a leading program in the synthesis of new materials by assembly of nanoscale components, and state-of-the-art electron microscopy and optical spectroscopy capabilities for studying the 3-D structure of these materials and their interaction with light. All of these characterization capabilities are available to the nanoscience research community through the CFN user program. We look forward to seeing the advances in nano-assembly that emerge as scientists across academia, industry, and government make use of the capabilities in their research.” 

    Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit

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    A Challenging Future for Tropical Forests

    Mortality rates of moist tropical forests are on the rise due to environmental drivers and related mechanisms.

    Stronger, lighter, greener

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    In a recent study from the U.S. Department of Energy's (DOE) Argonne National Laboratory, scientists have combined two membrane-bound protein complexes to perform a complete conversion of water molecules to hydrogen and oxygen.

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    Argonne scientist elected as SAE Fellow

    Scientist Michael Wang from the U.S. Department of Energy's (DOE) Argonne National Laboratory was recently inducted as a Fellow of the professional engineering organization SAE (Society of Automotive Engineers). The organization reserves this prestigious grade of membership for thosewho have made significant contributions to mobility technology and have demonstrated leadership in their field.

    Top 10 Discoveries of 2018

    Every year, the U.S. Department of Energy's (DOE) Brookhaven National Laboratory compiles a list of the biggest advances made by the Lab's staff scientists, engineers, and visiting researchers. From uncovering mysteries of the universe to building better batteries, here, in no particular order, are our picks for the top 10 discoveries of 2018.

    U.S. Department of Energy Announces $33 Million for Small Business Research and Development Grants

    The U.S. Department of Energy announced it will award 189 grants totaling $33 million to 149 small businesses in 32 states.

    DOE to Provide $16 Million for New Research into Atmospheric and Terrestrial Processes

    The U.S. Department of Energy (DOE) announced a plan to provide $16 million for new observational research aimed at improving the accuracy of today's climate and earth system models.

    Machine learning award powers Argonne leadership in engine design

    When attempting to design engines to be more fuel-efficient and emissions-free, automotive manufacturers have to take into account all the complexity inherent in the combustion process.

    ORNL partners with industry to address multiple nuclear technology challenges

    The Department of Energy's Oak Ridge National Laboratory is collaborating with industry on six new projects focused on advancing commercial nuclear energy technologies that offer potential improvements to current nuclear reactors and move new reactor designs closer to deployment.

    Lithium earns honors for three physicists working to bring the energy that powers the sun to Earth

    Feature describes research of three PPPL physicists who have won the laboratory's 2018 outstanding research awards

    DOE approves technical plan and cost estimate to upgrade Argonne facility; Project will create X-rays that illuminate the atomic scale, in 3D

    The U.S. Department of Energy has approved the technical scope, cost estimate and plan of work for an upgrade of the Advanced Photon Source, a major storage-ring X-ray source at Argonne.

    Costas Soukoulis elected to National Academy of Inventors

    Costas Soukoulis, Ames Laboratory senior scientist and Iowa State University Frances M. Craig Endowed Chair and Distinguished Professor, has been named as a 2018 National Academy of Inventors (NAI) Fellow.

    Biophysicist F. William Studier Elected Fellow of the National Academy of Inventors

    F. William Studier, a Senior Biophysicist Emeritus at the U.S. Department of Energy's Brookhaven National Laboratory and Adjunct Professor of Biochemistry at Stony Brook University, has been elected as a Fellow of the National Academy of Inventors (NAI). He is among 148 renowned academic inventors being recognized by NAI for 2018.

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    Observing Clouds in Four Dimensions

    Six cameras are revolutionizing observations of shallow cumulus clouds.

    A Challenging Future for Tropical Forests

    Mortality rates of moist tropical forests are on the rise due to environmental drivers and related mechanisms.

    Rapid Lake Draining on Ice Sheets Changes How Water Moves in Unexpected Ways

    Widespread fracturing during lake drainage triggers vertical shafts to form that affect the Greenland Ice Sheet.

    New Historical Emissions Trends Estimated with the Community Emissions Data System

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    Peering into the Mist: How Water Vapor Changes Metal at the Atomic Level

    New insights into molecular-level processes could help prevent corrosion and improve catalytic conversion.

    Microbial Types May Prove Key to Gas Releases from Thawing Permafrost

    Scientists discover key types of microbes that degrade organic matter and release carbon dioxide and methane into the atmosphere.

    New Method Knocks Out Yeast Genes with Single-Point Precision

    Researchers can precisely study how different genes affect key properties in a yeast used industrially to produce fuel and chemicals.

    How Plants Regulate Sugar Deposition in Cell Walls

    Identified genes involved in plant cell wall polysaccharide production and restructuring could aid in engineering bioenergy crops.

    Scientists Identify Gene Cluster in Budding Yeasts with Major Implications for Renewable Energy

    How yeast partition carbon into a metabolite may offer insights into boosting production for biofuels.

    More Designer Peptides, More Possibilities

    A combined experimental and modeling approach contributes to understanding small proteins with potential use in industrial, therapeutic applications.


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