Fig. 1. An illustration showing how highly nanostructured 3D superconducting materials can be created based on DNA self-assembly.Researchers have harnessed the ability of DNA to self-assemble to create three-dimensional (3D) nanoscale superconducting structures [Shani et al., Nature Communications (2020) 11:5697, https://doi.org/10.1038/s41467-020-19439-9].
Nanoscale superconducting structures have unique properties that could be useful for applications such as signal amplifiers in quantum computers, ultrasensitive magnetic field sensors for medical imaging and the mapping of materials below the surface. But traditional lithographic techniques can only produce one- or two-dimensional superconducting structures such as nanowires or thin films.
Now, researchers from the U.S. Department of Energy’s Brookhaven National Laboratory, Columbia University, and Bar-Ilan University in Israel have devised a ‘bottom-up’ approach that uses DNA-based self-assembly methods to construct 3D superconducting nanostructures. In DNA origami, a long single strand of DNA, helped by multiple shorter ‘staple’ strands, self-folds into a 3D structure, just like the ancient Japanese art of paper folding. Since the staple strands bind to the single strand DNA in specific places, a highly precise and complex structure can be predetermined.
Because of its structural programmability, DNA can provide an assembly platform for building designed nanostructures, explains Oleg Gang, who led the work at Brookhaven’s Center for Functional Nanomaterials (CFN) and is also a professor of chemical engineering, applied physics and materials science at Columbia. In this study, we show how DNA can serve as a scaffold for building 3D nanoscale architectures that can be fully ‘converted’ into inorganic materials like superconductors.
The team initially created octahedral DNA frames with embedded gold nanoparticles to help with structural characterization. By connecting up the frames at their vertices, the researchers were able to fabricate 3D DNA superlattices with a 48 nm unit cell and a gold nanoparticle in each alternating layer (Fig. 1). The DNA superlattice is then transformed into a silica scaffold using a wet chemistry sol-gel process before finally coating in niobium (Nb) to create a superconducting nanostructure.
In its original form, DNA is completely unusable for processing with conventional nanotechnology methods, says Gang. But once we coat the DNA with silica, we have a mechanically robust 3D architecture on which we can deposit inorganic materials using these methods.
The final coating of the silica scaffold with Nb using room-temperature e-beam evaporation was performed carefully enough to ensure that all the inner layers were covered without filling in the spaces in the superlattice. Tight control of the evaporation rate and temperature also made sure that Nb did not penetrate all the way to the bottom of the scaffold, which could short out electrical measurements. The approach results in weakly connected Nb grains on the octahedral DNA structures.
Making 3D nanosuperconductors previously involved a very elaborate and difficult process using conventional fabrication techniques, points out Yosef Yeshurun of Bar-Ilan University and co-corresponding author of the paper. Here we found a relatively simple way using DNA structures.
The resulting arrangement resembles a 3D array of superconducting Josephson bridges, which could be used in a variety of applications from 3D superconducting quantum interference devices (SQUIDs) for measuring magnetic fields and highly sensitive superconducting quantum interference filters (SQIFs) to amplifiers for quantum computers. These highly complex 3D superconducting structures could not easily be created by other conventional methods and could open the way to fabricating other types of nanoscale superlattice.
We have demonstrated a pathway for using complex DNA organizations to create highly nanostructured 3D superconducting materials, says Gang. This material conversion pathway gives us the ability to make a variety of systems with interesting properties – not only superconductivity, but also other electronic, mechanical, optical, and catalytic properties.
Gang describes this approach as a kind of ‘molecular lithography’ where the power of DNA’s programmability is exploited in 3D inorganic nanofabrication. The researchers now plan to create more complex 3D superconductive arrays for use in sensing and information processing.
This article originally appeared in Nano Today 36 (2021) 101071.