03/05/2018 | Press release | Distributed by Public on 03/08/2018 02:22
M.Sc. Boxuan Shen defends his doctoral dissertation in Physics 'Applications of DNA selfassembled structures in nano-electronics and plasmonics'. Opponent Professor Tim Liedl (Ludwig-Maximilians Universitat, Germany) and Custos Associate Professor Jussi Toppari (University of Jyväskylä). The doctoral dissertation is held in English.
The main focus of the thesis of Shen is to explore the possibilities of using DNA molecule as a tool to build miniature optical and electronic devices, e.g., optical bowtie antennas and single-electron-transistors.
DNA nanotechnology is an emerging field, in which DNA molecules are programmed to form nanoscale structures by self-assembly. Millions of DNA nanostructures with the same designed shape can be assembled simultaneously in a test tube.
- 'As a physicist, I am interested in using these fascinating DNA structures for physical applications. However, the electrical and optical properties of DNA are not optimal.', says Shen.
To address this challenge, a novel fabrication method to precisely transfer the shapes of DNA structures to gold objects on transparent substrate has been developed. These gold nanostructures have intriguing optical properties, e.g., optical bowtie antennas, which were fabricated on a sapphire chip, can be used to detect trace amount of molecules for diagnostic purpose. The fabrication method is also compatible with large-scale production thanks to the parallel assembling of DNA. In the future, if the metallic structures can be arranged in an ordered lattice, novel materials enabling phenomena like invisible cloaking or super lens, can even be realized.
- 'Another challenge to use these miniature DNA structures is to incorporate them into macroscopic circuits. This is especially important for electronic applications. ' states Shen.
In the other part of his thesis, inhomogeneous electric field has been used to trap DNA-based structures between gold nanoelectrodes by a method called dielectrophoresis. One of the trapped structures, which combines a DNA scaffold with three gold nanoparticle, is a promising candidate for a single-electron-transistor (SET). The SET has attracted many attentions recently because of its tiny size and extremely low power consumption. A behavior resembling SET has been observed on such device from low temperatures up to the room temperature.
In this thesis, the potential applications of DNA self-assembled structures were explored in both nanoelectronics and plasmonics. The works can be divided into two parts: electrical characterization of unmodified multilayered DNA origami and DNA-gold-nanoparticle conjugates after they were trapped between gold nanoelectrodes by dielectrophoresis, and the development of a novel fabrication method using DNA origami as a template for smooth, high resolution metallic nanostructures as well as optical characterization of them.
One of the biggest challenges in self-assembled nanoelectronic devices is to connect them to macroscopic circuits. Dielectrophoretic (DEP) trapping has been used extensively in manipulation of micro- and nanoscale objects in solution. We have demonstrated this technique by trapping four structurally distinct multilayered DNA origami between gold nanoelectrodes by DEP and electrically characterized some of the trapped structures at high relative humidity. Most of the samples showed insulating behavior in both DC I-V measurement and AC impedance spectroscopy. In the other experiment, an assembly of three gold nanoparticles (AuNPs) conjugated with a triple-cross-over-tile (TX-tile) structure were designed, synthesized, and trapped by DEP. At the beginning no current was observed, but after a few chemical gold growth steps, Coulomb blockade behavior was observed from the liquid helium temperature up to the room temperature. Although no gated measurement was carried out, the random switching at low temperature measurements highly resembled a similar behavior of single electron transistor (SET).
The second half of this thesis is focused on the development of a DNA-assisted lithography (DALI) method, in which DNA origami was used to mask the growth of SiO2 on Si chips in order to generate a stencil mask with openings of the DNA origami shape. Then the stencil was used in conventional microfabrication processes to deposit metallic nanostructures with almost the same shape as DNA origami on different substrates. Three different DNA origami were used to fabricate metallic structures with various optical properties on sapphire substrates. The localized surface plasmon resonance (LSPR) of Seeman tile and a bowtie antenna was characterized by a dark-field microscope. The surface enhanced Raman spectroscopy (SERS) of two different marker molecules on gold bowtie antennas was characterized too. Finally, the chiral double-L samples landed on a surface with different orientation combinations showed distinct circular dichroism (CD) spectra. In addition, a method to deposit DNA origami on unmodified surface with large area by spray coating technique was reported.