Tag Archives: Yugang Zhang

Innerspace of a nanoparticle

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A Jan. 3, 2019 news item on ScienceDaily touts a new means of transporting DNA-coated nanoparticles (DNA is deoxyribonucleic acid),

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 [2018] in ACS Central Science, a journal of the American Chemical Society (ACS).

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A January 3, 2018 Brookhaven National Laboratory (BNL) news release (also on EurekAlert), which originated the news item, explains the work in more detail (Note: Links have been removed),

“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.”

Here’s a link to and a citation for the paper,

Tailoring Surface Opening of Hollow Nanocubes and Their Application as Nanocargo Carriers by Fang Lu, Huolin Xin, Weiwei Xia, Mingzhao Liu, Yugang Zhang, Weiping Cai, and Oleg Gang. ACS Cent. Sci., 2018, 4 (12), pp 1742–1750 DOI: 10.1021/acscentsci.8b00778 Publication Date (Web): December 12, 2018

Copyright © 2018 American Chemical Society

This paper is open access.

DNA (deoxyribonucleic acid) scaffolding for nonbiological construction

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DNA (deoxyribonucleic acid) is being exploited in ways that would have seemed unimaginable to me when I was in high school. Earlier today (June 3, 2015), I ran a piece about DNA and data storage as imagined in an art/science project (DNA (deoxyribonucleic acid), music, and data storage) and now I have this work from the US Department of Energy’s (DOE) Brookhaven National Laboratory, from a June 1, 2015 news item on Nanowerk,

You’re probably familiar with the role of DNA as the blueprint for making every protein on the planet and passing genetic information from one generation to the next. But researchers at Brookhaven Lab’s Center for Functional Nanomaterials have shown that the twisted ladder molecule made of complementary matching strands can also perform a number of decidedly non-biological construction jobs: serving as a scaffold and programmable “glue” for linking up nanoparticles. This work has resulted in a variety of nanoparticle assemblies, including composite structures with switchable phases whose optical, magnetic, or other properties might be put to use in dynamic energy-harvesting or responsive optical materials. Three recent studies showcase different strategies for using synthetic strands of this versatile building material to link and arrange different types of nanoparticles in predictable ways.

The researchers have provided an image of the DNA building blocks,

Controlling the self-assembly of nanoparticles into superlattices is an important approach to build functional materials. The Brookhaven team used nanosized building blocks—cubes or octahedrons—decorated with DNA tethers to coordinate the assembly of spherical nanoparticles coated with complementary DNA strands.

Controlling the self-assembly of nanoparticles into superlattices is an important approach to build functional materials. The Brookhaven team used nanosized building blocks—cubes or octahedrons—decorated with DNA tethers to coordinate the assembly of spherical nanoparticles coated with complementary DNA strands.

A June 1, 2015 article (which originated the news item) in DOE Pulse Number 440 goes on to highlight three recent DNA papers published by researchers at Brookhaven National Laboratory,

The first [leads to a news release], published in Nature Communications, describes how scientists used the shape of nanoscale building blocks decorated with single strands of DNA to orchestrate the arrangement of spheres decorated with complementary strands (where bases on the two strands pair up according to the rules of DNA binding, A to T, G to C). For example, nano-cubes coated with DNA tethers on all six sides formed regular arrays of cubes surrounded by six nano-spheres. The attractive force of the DNA “glue” keeps these two dissimilar objects from self-separating to give scientists a reliable way to assemble composite materials in which the synergistic properties of different types of nanoparticles might be put to use.

In another study [leads to a news release], published in Nature Nanotechnology, the team used ropelike configurations of the DNA double helix to form a rigid geometrical framework, and added dangling pieces of single-stranded DNA to glue nanoparticles in place on the vertices of the scaffold. Controlling the code of the dangling strands and adding complementary strands to the nanoparticles gives scientists precision control over particle placement. These arrays of nanoparticles with predictable geometric configurations are somewhat analogous to molecules made of atoms, and can even be linked end-to-end to form polymer-like chains, or arrayed as flat sheets. Using this approach, the scientists can potentially orchestrate the arrangements of different types of nanoparticles to design materials that regulate energy flow, rotate light, or deliver biomolecules.

“We may be able to design materials that mimic nature’s machinery to harvest solar energy, or manipulate light for telecommunications applications, or design novel catalysts for speeding up a variety of chemical reactions,” said Oleg Gang, the Brookhaven physicist who leads this work on DNA-mediated nano-assembly.

Perhaps most exciting is a study [leads to a news release] published in Nature Materials in which the scientists added “reprogramming” strands of DNA after assembly to rearrange and change the phase of nanoparticle arrays. This is a change at the nanoscale that in some ways resembles an atomic phase change—like the shift in the atomic crystal lattice of carbon that transforms graphite into diamond—potentially producing a material with completely new properties from the same already assembled nanoparticle array. Inputting different types of attractive and repulsive reprogramming DNA strands, scientists could selectively trigger the transformation to the different resulting structures.

“The ability to dynamically switch the phase of an entire superlattice array will allow the creation of reprogrammable and switchable materials wherein multiple, different functions can be activated on demand,” Gang said.

Here are links to and citation for all three papers,

Superlattices assembled through shape-induced directional binding by Fang Lu, Kevin G. Yager, Yugang Zhang, Huolin Xin, & Oleg Gang. Nature Communications 6, Article number: 6912 doi:10.1038/ncomms7912 Published 23 April 2015

Prescribed nanoparticle cluster architectures and low-dimensional arrays built using octahedral DNA origami frames by Ye Tian, Tong Wang, Wenyan Liu, Huolin L. Xin, Huilin Li, Yonggang Ke, William M. Shih, & Oleg Gang. Nature Nanotechnology (2015) doi:10.1038/nnano.2015.105 Published online 25 May 2015

Selective transformations between nanoparticle superlattices via the reprogramming of DNA-mediated interactions by Yugang Zhang, Suchetan Pal, Babji Srinivasan, Thi Vo, Sanat Kumar & Oleg Gang. Nature Materials (2015) doi:10.1038/nmat4296 Published online 25 May 2015

The first study is open access, the second is behind a paywall but there is a free preview via ReadCube Acces, and the third is behind a paywall.

Mixing and matching your nanoparticles

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An Oct. 20, 2013 Brookhaven National Laboratory (BNL; US Dept. of Energy) news release (also on EurekAlert) describes a technique for combining different kinds of nanoparticles into a single nanocomposite,

Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have developed a general approach for combining different types of nanoparticles to produce large-scale composite materials. The technique, described in a paper published online by Nature Nanotechnology on October 20, 2013, opens many opportunities for mixing and matching particles with different magnetic, optical, or chemical properties to form new, multifunctional materials or materials with enhanced performance for a wide range of potential applications.

The approach takes advantage of the attractive pairing of complementary strands of synthetic DNA—based on the molecule that carries the genetic code in its sequence of matched bases known by the letters A, T, G, and C. After coating the nanoparticles with a chemically standardized “construction platform” and adding extender molecules to which DNA can easily bind, the scientists attach complementary lab-designed DNA strands to the two different kinds of nanoparticles they want to link up. The natural pairing of the matching strands then “self-assembles” the particles into a three-dimensional array consisting of billions of particles. Varying the length of the DNA linkers, their surface density on particles, and other factors gives scientists the ability to control and optimize different types of newly formed materials and their properties.

The news release details some of the challenges the researchers faced,

… the scientists explored the effect of particle shape. “In principle, differently shaped particles don’t want to coexist in one lattice,” said Gang [Brookhaven physicist Oleg Gang]. “They either tend to separate into different phases like oil and water refusing to mix or form disordered structures.” The scientists discovered that DNA not only helps the particles mix, but it can also improve order for such systems when a thicker DNA shell around the particles is used.

They also investigated how the DNA-pairing mechanism and other intrinsic physical forces, such as magnetic attraction among particles, might compete during the assembly process. For example, magnetic particles tend to clump to form aggregates that can hinder the binding of DNA from another type of particle. “We show that shorter DNA strands are more effective at competing against magnetic attraction,” Gang said.

For the particular composite of gold and magnetic nanoparticles they created, the scientists discovered that applying an external magnetic field could “switch” the material’s phase and affect the ordering of the particles. “This was just a demonstration that it can be done, but it could have an application—perhaps magnetic switches, or materials that might be able to change shape on demand,” said Zhang [[Yugang Zhang, first author of the paper].

The third fundamental factor the scientists explored was how the particles were ordered in the superlattice arrays: Does one type of particle always occupy the same position relative to the other type—like boys and girls sitting in alternating seats in a movie theater—or are they interspersed more randomly? “This is what we call a compositional order, which is important for example for quantum dots because their optical properties—e.g., their ability to glow—depend on how many gold nanoparticles are in the surrounding environment,” said Gang. “If you have compositional disorder, the optical properties would be different.” In the experiments, increasing the thickness of the soft DNA shells around the particles increased compositional disorder.

These fundamental principles give scientists a framework for designing new materials. The specific conditions required for a particular application will be dependent on the particles being used, Zhang emphasized, but the general assembly approach would be the same.

Said Gang, “We can vary the lengths of the DNA strands to change the distance between particles from about 10 nanometers to under 100 nanometers—which is important for applications because many optical, magnetic, and other properties of nanoparticles depend on the positioning at this scale. We are excited by the avenues this research opens up in terms of future directions for engineering novel classes of materials that exploit collective effects and multifunctionality.”

Here’s a link to and a citation for the research paper,

A general strategy for the DNA-mediated self-assembly of functional nanoparticles into heterogeneous systems by Yugang Zhang, Fang Lu, Kevin G. Yager, Daniel van der Lelie, & Oleg Gang. Nature Nanotechnology (2013) doi:10.1038/nnano.2013.209 Published online 20 October 2013.

This article can be viewed/previewed on ReadCube or purchased.