DNA origami imaged with different methods. Top left, a DNA origami sample after cryo etch, imaged with SEM. Left middle, a deconvoluted image of DNA origami tubes, imaged with confocal microscopy. Bottom left, DNA origami lattice on silicon, imaged with AFM in air. Top right, DNA origami lattice sample after SIO2 growth, imaged with HIM. Right bottom, DNA origami tubes assembled in liquid and imaged with cryo-TEM. Credit: Johannes Parikka, Nanofabrication using DNA nanotechnology. http://urn.fi/URN:ISBN:978-952-86-1191-2
A dissertation study at the University of Jyväskylä (Finland) developed two-dimensional fishnet-like structures from DNA origami for silicon surfaces and investigated how different conditions affect their formation. The results provide new possibilities for DNA-assisted lithography and thus for the fabrication of new types of materials, for example, for optics.
In his doctoral thesis research, Doctoral Researcher Johannes Parikka from the University of Jyväskylä fabricated fishnet-type two-dimensional (2D) DNA origami lattices on silicon.
"DNA origami are nanoscale structures composed of single-stranded DNA. They can interact with each other, forming larger lattice structures," says Parikka.
Earlier, similar lattices have been made only on mica, which, as a fragile mineral, is not compatible with any subsequent microfabrication methods, such as etching. DNA origami lattices on silicon open the possibility to utilize DNA-assisted lithography, which further enables the fabrication of a new type of material.
"The largest single crystal lattice assembled on silicon was 5.6 µm2 in area, which means around 560 individual DNA origami. For this particular design and silicon substrate, it is the largest result ever achieved," says Parikka.
Versatile DNA origami
The research utilized the self-assembly of DNA origami structures on silicon, where they can form larger 2D lattices. DNA origami and the treated silicon substrate are both negatively charged. Divalent cations, such as Mg2+, can therefore attach DNA origami to the surface. The interaction strength between the DNA origami and the surface can be tuned with a monovalent cation, such as Na+, that is, by table salt (NaCl).
"The Na+ ions of added table salt replace some of the attaching Mg2+ ions, which increases the DNA origami mobility on the surface, enabling the lattice assembly," says Parikka.
During the research, it was determined how deposition conditions, such as temperature and salt concentrations, affect the lattice formation. Structures were mostly imaged using atomic force microscopy (AFM).
"During the research, it was also noticed that by tuning the conditions, mainly sample solution salt concentrations, DNA origami lattices could be rolled into tubular structures in solution. In addition, the same DNA origami, with slight modifications, could be used to form controlled nanoparticle lattices," states Parikka.
Towards metamaterial fabrication
The results presented in this thesis are important for DNA origami lattice fabrication on silicon and thus also for photonics, since it enables metallization of the structures by DNA-assisted lithography. Metallic lattices, compared to individual DNA origami, enhance the optical response better and enable the fabrication of a metamaterial.
"Metamaterials have a certain property, such as a negative refractive index, which cannot be found in materials found in nature," explains Parikka.
Parikka completed his master's thesis in 2020 at the Department of Chemistry and started his Ph.D. research at the Department of Physics and the Nanoscience Center. The supervisor for the doctoral thesis is Professor Jussi Toppari.
MSc Parikka's thesis, titled "Nanofabrication using DNA nanotechnology," public examination will be held on Friday, 19th of December at 12:00. The opponent is Professor Tim Liedl (Ludwig-Maximilians-Universität München), and the custos is Professor Jussi Toppari (University of Jyväskylä). Public examination is held in English.
Provided by University of Jyväskylä
