Topic Name: BNL Researchers Used DNA for the First time to Yields 3-D Crystalline Organization of Nanoparticles
Research persons: Brookhaven National Laboratory Research Team
Location: Brookhaven National Laboratory, U.S. Department of Energy, United States
In an achievement some see as the "holy grail" of nanoscience,
researchers at the U.S.
Department of Energy's Brookhaven
National Laboratory have for the first time used DNA
to guide the creation of three-dimensional, ordered, crystalline structures of
nanoparticles (particles with dimensions measured in billionths of a meter). The
ability to engineer such 3-D structures is essential to producing functional
materials that take advantage of the unique properties that may exist at the
nanoscale - for example, enhanced magnetism, improved catalytic activity, or new
"From previous research, we know that highly selective DNA binding can
be used to program nanoparticle interactions," said Oleg Gang, a scientist
at Brookhaven's Center for
Functional Nanomaterials (CFN), who led the interdisciplinary research team,
which includes Dmytro Nykypanchuk and Mathew Maye of the CFN, and Daniel van der
Lelie of the Biology Department. "But while theory has intriguingly
predicted that DNA can guide nanoparticles to form ordered, 3-D phases, no one
has accomplished this experimentally, until now."
As with the group's previous work, the new assembly method relies on the
attractive forces between complementary strands of DNA - the molecule made of
pairing bases known by the letters A, T, G, and C that carries the genetic code
of living things. First, the scientists attach to nanoparticles hair-like
extensions of DNA with specific "recognition sequences" of
complementary bases. Then they mix the DNA-covered particles in solution. When
the recognition sequences find one another in solution, they bind together to
link the nanoparticles.
This first binding is necessary, but not sufficient, to produce the organized
structures the scientists are seeking. To achieve ordered crystals, the
scientists alter the properties of DNA and borrow some techniques known for
Importantly, they heat the samples of DNA-linked particles and then cool them
back to room temperature. "This 'thermal processing' is somewhat similar to
annealing used in forming more common crystals made from atoms," explained
Nykypanchuk. "It allows the nanoparticles to unbind, reshuffle, and find
more stable binding arrangements."
The team also experimented with different degrees of DNA flexibility,
recognition sequences, and DNA designs in order to find a "sweet spot"
of interactions where a stable, crystalline form would appear.
Results from a variety of analysis techniques, including small angle x-ray
scattering at the National
Synchrotron Light Source and dynamic light scattering and different types of
optical spectroscopies and electron microscopy at the CFN, were combined to
reveal the detail of the ordered structures and the underlying processes for
their formation. These results indicate that the scientists have indeed found
that sweet spot to create 3-D nanoparticle assemblies with long-range
crystalline order using DNA. The crystals are remarkably open, with the
nanoparticles themselves occupying only 5 percent of the crystal lattice volume,
and DNA occupying another 5 percent. "This open structure leaves a lot of
room for future modifications, including the incorporation of different nano-objects
which will lead to enhanced nanoscale properties and new classes of
applications," said Maye. For example, pairing gold nanoparticles with
other metals often improves catalytic activity. Additionally, the DNA linking
molecules can be used as a kind of chemical scaffold for adding small molecules,
polymers, or proteins.
Furthermore, once the crystal structure is set, it remains stable through
repeated heating and cooling cycles, a feature important to many potential
The crystals are also extraordinarily sensitive to thermal expansion - 100
times more sensitive than ordinary materials, probably due to the heat
sensitivity of DNA. This significant thermal expansion could be a plus in
controlling optical and magnetic properties, for example, which are strongly
affected by changes in the distance between particles. The ability to effect
large changes in these properties underlies many potential applications such as
energy conversion and storage, as well as sensor technology.
The Brookhaven team worked with gold nanoparticles as a model, but they say
the method can be applied to other nanoparticles as well. And they fully expect
the technique could yield a wide array of crystalline phases with different
types of 3-D lattices that could be tailored to particular functions.
"This work is the first step to demonstrate that it is possible to
obtain ordered structures. But it opens so many avenues for researchers, and
this is why it is so exciting," Gang says.
Note for Nanoparticle
A nanoparticle is a small particle with at least one dimension less than 100 nm. Nanoparticle research is currently an area of intense scientific research, due to a wide variety of potential applications in biomedical, optical, and electronic fields. The National Nanotechnology Initiative of the United States government has driven huge amounts of state funding exclusively for nanoparticle research.
Nanoparticles are of great scientific interest as they are effectively a bridge between bulk materials and atomic or molecular structures. A bulk material should have constant physical properties regardless of its size, but at the nano-scale this is often not the case. Size-dependent properties are observed such as quantum confinement in semiconductor particles, surface plasmon resonance in some metal particles and superparamagnetism in magnetic materials.
The properties of materials change as their size approaches the nanoscale and as the percentage of atoms at the surface of a material becomes significant. For bulk materials larger than one micrometre the percentage of atoms at the surface is minuscule relative to the total number of atoms of the material. The interesting and sometimes unexpected properties of nanoparticles are partly due to the aspects of the surface of the material dominating the properties in lieu of the bulk properties.
Nanoparticles exhibit a number of special properties relative to bulk material. For example, the bending of bulk copper (wire, ribbon, etc.) occurs with movement of copper atoms/clusters at about the 50 nm scale. Copper nanoparticles smaller than 50 nm are considered super hard materials that do not exhibit the same malleability and ductility as bulk copper. The change in properties is not always desirable. Ferroelectric materials smaller than 10 nm can switch their magnetisation direction using room temperature thermal energy, thus making them useless for memory storage. Suspensions of nanoparticles are possible because the interaction of the particle surface with the solvent is strong enough to overcome differences in density, which usually result in a material either sinking or floating in a liquid. Nanoparticles often have unexpected visible properties because they are small enough to confine their electrons and produce quantum effects. For example gold nanoparticles appear deep red to black in solution.
Note for Dynamic Light Scattering
Dynamic light scattering (also known as Photon Correlation Spectroscopy) is a powerful technique in physics, which can be used to determine the size distribution profile of small particles in solution.
When light hits small particles the light scatters in all directions (Rayleigh scattering) so long as the particles are small compared to the wavelength (< 250 nm). If the light source is a laser, and thus is monochromatic and coherent, then one observes a time-dependent fluctuation in the scattering intensity. These fluctuations are due to the fact that the small molecules in solutions are undergoing Brownian motion and so the distance between the scatterers in the solution is constantly changing with time. This scattered light then undergoes either constructive or destructive interference by the surrounding particles and within this intensity fluctuation information is contained about the time scale of movement of the scatterers.
There are several ways to derive dynamic information about particles’ movement in solution by Brownian motion. One of such methods is dynamic light scattering, also known as quasi elastic laser light scattering. The dynamic information of the particles is derived from an autocorrelation of the intensity trace recorded during the experiment.
Note for Transmission Electron Microscopy
Transmission electron microscopy (TEM) is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through it. An image is formed from the electrons transmitted through the specimen, magnified and focused by an objective lens and appears on an imaging screen, a fluorescent screen in most TEMs, plus a monitor, or on a layer of photographic film, or to be detected by a sensor such as a CCD camera. The first practical transmission electron microscope was built by Albert Prebus and James Hillier at the University of Toronto in 1938 using concepts developed earlier by Max Knoll and Ernst Ruska.
Theoretically the maximum resolution that one can obtain with a light microscope has been limited by the wavelength of the photons that are being used to probe the sample and the numerical aperture of the system. Early twentieth century scientists theorized ways of getting around the limitations of the relatively large wavelength of visible light (wavelengths of 400–700 nanometers) by using electrons. Like all matter, electrons have both wave and particle properties (as theorized by Louis-Victor de Broglie), and their wave-like properties mean that a beam of electrons can be made to behave like a beam of electromagnetic radiation.
About National Synchrotron Light Source
The National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory (BNL) in Upton, New York is a national user research facility funded by the U.S. Department of Energy (DOE).
The NSLS experimental floor consists of two electron storage rings: an X-Ray ring and a VUV (Vacuum Ultra Violet) Ring which provide intense focused light spanning the electromagnetic spectrum from the infrared through x-rays. The properties of this light and the specially designed experimental stations, called beamlines, allow scientists in many fields of research to perform experiments not otherwise possible at their own laboratories.
This research was funded by the Division
of Materials Science and Engineering in the Office of Basic Energy Sciences
within the U.S. Department of
Energy's Office of Science.
The Center for Functional Nanomaterials (CFN) is one of the five DOE
Nanoscale Science Research Centers (NSRCs), premier national user facilities for
interdisciplinary research at the nanoscale. Together the NSRCs comprise a suite
of complementary facilities that provide researchers with state-of-the-art
capabilities to fabricate, process, characterize, and model nanoscale materials,
and constitute the largest infrastructure investment of the National
Nanotechnology Initiative. The NSRCs are located at DOE's Brookhaven, Argonne,
Lawrence Berkeley, Oak Ridge, and Sandia and Los Alamos National Laboratories.
For more information about the DOE NSRCs.
One of ten national laboratories overseen and primarily funded by the Office
of Science of the U.S. Department of Energy (DOE), Brookhaven National
Laboratory conducts research in the physical, biomedical, and environmental
sciences, as well as in energy technologies and national security. Brookhaven
Lab also builds and operates major scientific facilities available to
university, industry and government researchers. Brookhaven is operated and
managed for DOE's Office of Science by Brookhaven Science Associates, a
limited-liability company founded by the Research Foundation of State University
of New York on behalf of Stony Brook University, the largest academic user of
Laboratory facilities, and Battelle, a nonprofit, applied science and technology
In figure 1, "Body-centered-cubic" unit cells of the 3-D nanoparticle crystals. One type of nanoparticle occupies each corner of the cube and a second type of nanoparticle is located centrally inside. These unit cells, measuring tens of nanometers, form a repeating lattice that extends more than a micron (1,000 nanometers) in three dimensions.
In figure 2, Researchers Matthew Maye, Niels van der Lelie, Oleg Gang, and Dmytro Nykypanchuk.
In figure 3, A beamline for synchrotron light at Brookhaven
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