A schematic of the programmable assembly of 3D ordered nanostructures from material voxels that can carry inorganic or organic nanoparticles with different functions, including light emitters and absorbers, proteins, and enzymes with chemical activity. Image: Brookhaven National Laboratory.Scientists have developed a platform for assembling nanosized material components, or ‘nano-objects’, of very different types – inorganic or organic – into desired three-dimensional (3D) structures.
Though self-assembly (SA) has successfully been used to organize nanomaterials of several kinds, the process has been extremely system-specific, generating different structures based on the intrinsic properties of the nanomaterials. As the scientists report in a paper in Nature Materials, their new DNA-programmable nanofabrication platform can organize a variety of 3D materials in the same prescribed ways at the nanoscale, where unique optical, chemical and other properties can emerge.
"One of the major reasons why SA is not a technique of choice for practical applications is that the same SA process cannot be applied across a broad range of materials to create identical 3D-ordered arrays from different nanocomponents," explained corresponding author Oleg Gang, leader of the Soft and Bio Nanomaterials Group at Brookhaven National Laboratory’s Center for Functional Nanomaterials (CFN) and a professor of chemical engineering and of applied physics and materials science at Columbia Engineering. "Here, we decoupled the SA process from material properties by designing rigid polyhedral DNA frames that can encapsulate various inorganic or organic nano-objects, including metals, semiconductors, and even proteins and enzymes."
The scientists engineered synthetic DNA frames in the shape of a cube, octahedron and tetrahedron. Inside the frames are DNA ‘arms’ that only nano-objects with the complementary DNA sequence can bind to. The resulting material voxels, integrating the DNA frame and nano-object, are the building blocks from which macroscale 3D structures can be made.
The frames connect to each other regardless of what kind of nano-object is inside (or not), according to complementary DNA sequences encoded at their vertices. Depending on their shape, the frames have a different number of vertices and thus form entirely different structures. Any nano-objects hosted inside the frames take on that specific frame structure.
To demonstrate their assembly approach, the scientists selected metallic (gold) and semiconducting (cadmium selenide) nanoparticles and a bacterial protein (streptavidin) as the inorganic and organic nano-objects to be placed inside the DNA frames. First, they confirmed the integrity of the DNA frames and the formation of material voxels by imaging with electron microscopes at the CFN Electron Microscopy Facility and the Van Andel Institute, which has a suite of instruments that operate at cryogenic temperatures for biological samples.
They then probed the 3D lattice structures at the Coherent Hard X-ray Scattering and Complex Materials Scattering beamlines of the National Synchrotron Light Source II (NSLS-II) at Brookhaven Lab. Sanat Kumar, a professor of chemical engineering at Columbia Engineering, and his group performed computational modeling to reveal that the experimentally observed lattice structures (based on the X-ray scattering patterns) were the most thermodynamically stable ones that the material voxels could form.
"These material voxels allow us to begin to use ideas derived from atoms (and molecules) and the crystals that they form, and port this vast knowledge and database to systems of interest at the nanoscale," explained Kumar.
Gang's students at Columbia Engineering then demonstrated how the assembly platform could be used to drive the organization of two different kinds of materials, one with chemical functions and one with optical functions. For the chemical material demonstration, the scientists co-assembled two enzymes, creating 3D arrays with a high packing density. Though the enzymes remained chemically unchanged, they showed about a four-fold increase in enzymatic activity. These ‘nanoreactors’ could be used to manipulate cascade reactions and enable the fabrication of chemically active materials.
For the optical material demonstration, the scientists mixed two different colors of quantum dots – tiny nanocrystals that are being used to make television displays with high color saturation and brightness. Images captured with a fluorescence microscope showed that the resulting lattice maintained color purity below the diffraction limit of light, which could allow for significant resolution improvement in various display and optical communication technologies.
"We need to rethink how materials can be formed and how they function," said Gang. "Material redesign may not be necessary; simply packaging existing materials in new ways could enhance their properties. Potentially, our platform could be an enabling technology 'beyond 3D printing manufacturing' to control materials at much smaller scales and with greater material variety and designed compositions. Using the same approach to form 3D lattices from desired nano-objects of different material classes, integrating those that would otherwise be considered incompatible, could revolutionize nanomanufacturing."
This story is adapted from material from Brookhaven National Laboratory, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.