Nanodevices by DNA based gold nanostructures

Abstract

In this thesis DNA based structures were utilized to create gold nanostructures for nanosensing and nanoelectronic applications. In the past, both of these fields have been dominated by the conventional lithography methods, e.g., electron beam lithography and UV-lithography, but more recently scaling down the components by these techniques has become increasingly more complex and costly. Especially in the micro- and nanoelectronics, the increase in the component density and thus computational power would require fabrication of sub-10-nm components, which is challenging for the top-down approaches. Aforementioned developments have led researchers to seek alternative methods to fabricate these components using so-called bottom-up approaches, that could offer less complex, faster and cost-efficient ways to fabricate the desired structures. Two of the most promising candidates for this task have been the deoxyribonucleic acid and metallic nanoparticles due to their unique optical, mechanical and chemical properties, which allow almost seamless interfacing between the two, yet still incorporate their essential optical and electrical properties, that is typically more difficult to achieve using other pairs of organic and inorganic compounds. Three distinct fabrication methods were investigated to create three different nanodevices. The new DNA assisted lithography method was used to create meta- surfaces covered with arbitrary, highly defined metallic shapes, e.g., nanoantenna bowties. The more traditional hybridization based patterning of gold nanoparticles on DNA template was used to create DNA and gold nanoparticle assemblies, which applicability as a single electron transistor was demonstrated. Finally, DNA and gold nanoparticle based assembly was utilized as an electric field controllable probe to investigate the folding and unfolding properties of a hairpin-DNA molecule. Metallic bowtie antennas have interested researchers due to the high field enhancement between the two triangles, which could be used in e.g. surface-enhanced Raman spectroscopy. However, the current fabrication techniques have been mostly limited to infrared region due to the size and shape restrictions. By using dark field microscopy, we have showed that the new fabrication method is able to produce highly defined structures in a wafer scale and having their desired optical properties at visible regions even on high-refractive index substrates, where both of the features have not been feasible to accomplice before. Single stranded DNA functionalized gold nanoparticles are one of the standard tools to develop nanoscale applications, from nanopatterning to diagnostic detection. Functionalization scheme using DNA and AuNPs was utilized to fabricate two vastly different assemblies: pearl-like, three gold nanoparticle linear chain on DNA template and AuNPs coated with biotinylated DNA strands, which were further immobilized to chimeric avidin coated gold surface via strong biotin-avidin interaction. For the former case, dielectrophoresis trapping was employed to position these pearl-like DNA-AuNP assemblies between a fingertip electrode structure for current-voltage characterization. It was observed that the plain, pearl-like DNA-AuNP assemblies did not conduct a current, which was most probably due to too large air gaps between the AuNPs. Thus the structures were extruded larger by chemical gold growth process. After that the current started to flow when a threshold voltage was reached, i.e, where after the Coulomb blockade was observed for a few samples from 4.2 K up to room temperature. For the latter case, the sandwich assembly of gold surface-avidin-DNA-AuNP was used to study the conformational changes of a hairpin-DNA by electric field induced motion of the AuNP, where the motion of gold nanoparticles either caused the DNA to stretch and unfold or relax and fold back.