Sung Ha Park

Programming DNA Tube Circumferences

Synthesizing molecular tubes with monodisperse, programmable circumferences is an important goal shared by nanotechnology, materials science, and supermolecular chemistry. We program molecular tube circumferences by specifying the complementarity relationships between modular domains in a 42-base single-stranded DNA motif. Single-step annealing results in the self-assembly of long tubes displaying monodisperse circumferences of 4, 5, 6, 7, 8, 10, or 20 DNA helices.

Optimized fabrication and electrical analysis of silver nanowires templated on DNA molecules

We report on the electrical conductivity measurement of silver nanowires templated on native λ-bacteriophage and synthetic double-stranded DNA molecules. After an electroless chemical deposition, the metallized DNA wires have a diameter down to 15nm and are among the thinnest metallic nanowires available to date. Two-terminal I-V measurements demonstrating various conduction behaviors are presented. DNA templated functional nanowires may, in the near future, be targeted to connect at specific locations on larger-scale circuits and represent a potential breakthrough in the self-assembly of nanometer-scale structures for electronics layout.

Electronic nanostructures templated on self-assembled DNA scaffolds

We report on the self-assembly of one- and two-dimensional DNA scaffolds, which serve as templates for the targeted deposition of ordered nanoparticles and molecular arrays .T he DNA nanostructures are easy to reprogram, and we demonstrate two distinct conformations: sheets and tubes. The DNA tubes and individual DNA molecules are metallized in solution to produce ultra-thin metal wires. (Some figures in this article are in colour only in the electronic version)

n- and p-Type Doping Phenomenon by Artificial DNA and M-DNA on Two-Dimensional Transition Metal Dichalcogenides

Deoxyribonucleic acid (DNA) and two-dimensional (2D) transition metal dichalcogenide (TMD) nanotechnology holds great potential for the development of extremely small devices with increasingly complex functionality. However, most current research related to DNA is limited to crystal growth and synthesis. In addition, since controllable doping methods like ion implantation can cause fatal crystal damage to 2D TMD materials, it is very hard to achieve a low-level doping concentration (nondegenerate regime) on TMD in the present state of technology. Here, we report a nondegenerate doping phenomenon for TMD materials (MoS2 and WSe2, which represent n- and p-channel materials, respectively) using DNA and slightly modified DNA by metal ions (Zn(2+), Ni(2+), Co(2+), and Cu(2+)), named as M-DNA. This study is an example of interdisciplinary convergence research between DNA nanotechnology and TMD-based 2D device technology. The phosphate backbone (PO4(-)) in DNA attracts and holds hole carriers in the TMD region, n-doping the TMD films. Conversely, M-DNA nanostructures, which are functionalized by intercalating metal ions, have positive dipole moments and consequently reduce the electron carrier density of TMD materials, resulting in p-doping phenomenon. N-doping by DNA occurs at ∼6.4 × 10(10) cm(-2) on MoS2 and ∼7.3 × 10(9) cm(-2) on WSe2, which is uniform across the TMD area. p-Doping which is uniformly achieved by M-DNA occurs between 2.3 × 10(10) and 5.5 × 10(10) cm(-2) on MoS2 and between 2.4 × 10(10) and 5.0 × 10(10) cm(-2) on WSe2. These doping levels are in the nondegenerate regime, allowing for the proper design of performance parameters of TMD-based electronic and optoelectronic devices (VTH, on-/off-currents, field-effect mobility, photoresponsivity, and detectivity). In addition, by controlling the metal ions used, the p-doping level of TMD materials, which also influences their performance parameters, can be controlled. This interdisciplinary convergence research will allow for the successful integration of future layered semiconductor devices requiring extremely small and very complicated structures.

Low-cost label-free electrical detection of artificial DNA nanostructures using solution-processed oxide thin-film transistors.

A high-sensitivity, label-free method for detecting deoxyribonucleic acid (DNA) using solution-processed oxide thin-film transistors (TFTs) was developed. Double-crossover (DX) DNA nanostructures with different concentrations of divalent Cu ion (Cu(2+)) were immobilized on an In-Ga-Zn-O (IGZO) back-channel surface, which changed the electrical performance of the IGZO TFTs. The detection mechanism of the IGZO TFT-based DNA biosensor is attributed to electron trapping and electrostatic interactions caused by negatively charged phosphate groups on the DNA backbone. Furthermore, Cu(2+) in DX DNA nanostructures generates a current path when a gate bias is applied. The direct effect on the electrical response implies that solution-processed IGZO TFTs could be used to realize low-cost and high-sensitivity DNA biosensors.

Coverage Control of DNA Crystals Grown by Silica Assistance

The impetus behind the current interest in combining DNA materials with conventional nanotechnologies, such as nanoelectronics, biosensors, and nanophotonics, emanates from an ambition to exploit its remarkable properties. One of these properties is self-assembly that is driven by the thermodynamics of sticky end hybridization and makes structural DNA nanotechnology a prime candidate for bottom-up fabrication schemes in these fields. However, unless self-assembled DNA nanostructures can be fabricated on solid surfaces to at least the degree of accuracy of existing top-down methods, it will be unfeasible to replace it with existing technologies. An intermediate step toward this goal has been to merge the two approaches such that DNA nanostructures are self-assembled onto lithographically patterned substrates. Previous works have been successful at depositing self-assembled DNA nanostructures on patterned substrates and controlling the spatial orientations of tailored DNA origami motifs at specifically designated sites. All these approaches have used random depositions (or similar methods) of preformed DNA structures onto lithographically patterned substrates. What has been lacking in literature is a method of precisely controlling the coverage of DNA structures on various substrates, that is, the percentage of the surface covered by crystals, especially on silica (SiO2), which is crucial if DNA is to be universally employed in electronics. We provide a solution to this problem by introducing a new surface-assisted fabrication method, termed the silica-assisted growth (SAG) method, to selfassemble DNA nanostructures on SiO2 surfaces. The novel fabrication technique presented herein bears two important distinctions from previous studies. Firstly, direct annealing on the substrates allows for very accurate control of the amount of DNA structures that self-assemble on the substrate, that is, the coverage. Secondly, because of electrostatic interactions with the silica surface, structures grown by this method show drastic topological changes that lead to previously unreported novel structures. The pretreatment process of SiO2 substrates and the various DNA structures grown on them are shown in Figure 1. Silanol groups on the SiO2 surface become deprotonated once the substrates are treated in a 10 TAE/Mg buffer (see the Experimental section for details) since the pH of this buffer exceeds the isoelectric point of SiO2. [13] This approach allows Mg ions to bind to the substrate surface, which in turn binds the negatively charged DNA backbones (Figure 1a). To demonstrate the SAG method, four different types of DNA nanostructures were prepared. 8 helix tubes (8 HT) and 5 helix ribbons (5 HR) were constructed from single-stranded tiles (SST), while double-crossover (DX) crystals and DX crystals with biotin modifications were fabricated from DX tiles (see Figure S1–S3 in the Supporting Information). The schematic diagrams of the various DNA structures are illustrated in Figure 1b–f and their corresponding AFM images on SiO2 substrates are shown in Figure 1g–p (Figure 1g–k show structures made from the free solution annealing method deposited onto SiO2 for imaging and Figure 1 l–p show structures made using the SAG method where the structures are annealed directly on the substrate, see Figure S4 in the Supporting Information). For the 8 HT, there is a dramatic difference between the structure formations of the free solution annealing method and the SAG method. Caused by a local minimum in the free energy landscape, monodisperse 8 HT structures on SiO2 fabricated from the free solution annealing method are stable, which can be clearly seen in Figure 1g. In this case, the structures have already been formed in solution before they are deposited onto the substrate. Meanwhile, in the case of SAG, the charges of the Mg ions bound on the substrate surface interact with the DNA strands to prevent the formation of tubes. Through these interactions, an acute topological change of the structures occurs, allowing SSTs to bind edgewise and to remain in a single-layer state (Figure 1 l) with some of the tiles overlapping along their boundaries (Figure 1 l, bright regions). To the best of our knowledge, this is the first observation of 2D crystals arising from SST motifs. Another type of 1D structure, the 5 helix ribbon, was also successfully fabricated using both the free solution annealing and SAG methods as can be seen in Figure 1h and m, respectively. The substrate acts as a catalyst to reduce the amount of energy needed for DNA structures to form, resulting in large-scale structure formations on the substrates. In the case of DX crystals, two-tile units of DXmonomers were used as building blocks to fabricate periodic arrays. One [*] J. Lee, J. Kim, Prof. S. H. Park Sungkyunkwan Advanced Institute of Nanotechnology (SAINT) and Department of Physics, Sungkyunkwan University Suwon 440-746 (Korea) E-mail: sunghapark@skku.edu S. Kim, Prof. Y. Roh School of Information and Communication Engineering, Sungkyunkwan University Suwon 440-746 (Korea) E-mail: yhroh@skku.edu

Copper-glucosamine microcubes: synthesis, characterization, and C-reactive protein detection.

Cubelike microstructures of glucosamine-functionalized copper (GlcN-CuMCs) have been fabricated by the integration of injection pump and ultrasonochemistry. Although bulk microstructures and the nanostructure of metallic copper exhibit distinct applications, the amino sugar surface-functionalized copper is almost biocompatible and exhibits advanced features such as more crystallinity, high thermal stability, and electrochemical feasibility toward biomolecule (C-reactive protein, CRP) detection. An electrochemical test of this GlcN-CuMCs was demonstrated by immobilization on a conventional gold-PCB (Au-PCB) electrode. The combination of a biointerface membrane, from glucosamine functionalization, and electroactive sites of metallic copper provides a very efficient electrochemical response against various concentration of CRP. A perfect scaling of steady-state currents with r(2) values of 0.9862 (I(pa)) and 0.9972 (I(pc)) indicate the promise of this kind of biofunctionalized microstructure electrode for many surface and interface applications.

Approaches to label-free flexible DNA biosensors using low-temperature solution-processed InZnO thin-film transistors.

Low-temperature solution-processed In-Zn-O (IZO) thin-film transistors (TFTs) exhibiting a favorable microenvironment for electron transfer by adsorbed artificial deoxyribonucleic acid (DNA) have extraordinary potential for emerging flexible biosensor applications. Superb sensing ability to differentiate even 0.5 μL of 50 nM DNA target solution was achieved through using IZO TFTs fabricated at 280 °C. Our IZO TFT had a turn-on voltage (V(on)) of -0.8 V, on/off ratio of 6.94 × 10(5), and on-current (I(on)) value of 2.32 × 10(-6)A in pristine condition. A dry-wet method was applied to immobilize two dimensional double crossover tile based DNA nanostructures on the IZO surface, after which we observed a negative shift of the transfer curve accompanied by a significant increase in the Ion and degradation of the Von and on/off ratio. As the concentration of DNA target solution increased, variances in these parameters became increasingly apparent. The sensing mechanism based on the current evolution was attributed to the oxidation of DNA, in which the guanine nucleobase plays a key role. The sensing behavior obtained from flexible biosensors on a polymeric substrate fabricated under the identical conditions was exactly analogous. These results compare favorably with the conventional field-effect transistor based DNA sensors by demonstrating remarkable sensitivity and feasibility of flexible devices that arose from a different sensing mechanism and a low-temperature process, respectively.

Magnetic Characteristics of Copper Ion-Modified DNA Thin Films

We developed a new method of fabricating a divalent copper ion (Cu2+) modified DNA thin film on a glass substrate and studied its magnetic properties. We evaluated the coercive field (Hc), remanent magnetization (Mr), susceptibility (χ), and thermal variation of magnetization with varying Cu2+ concentrations [Cu2+] resulting in DNA thin films. Although thickness of the two dimensional DNA thin film with Cu2+ in dry state was extremely thin (0.6 nm), significant ferromagnetic signals were observed at room temperature. The DNA thin films with a [Cu2+] near 5 mM showed the distinct S-shape hysteresis with appreciable high Hc, Mr and χ at low field (≤600 Oe). These were primarily caused by the presence of small magnetic dipoles of Cu2+ coordination on the DNA molecule, through unpaired d electrons interacting with their nearest neighbors and the inter-exchange energy in the magnetic dipoles making other neighboring dipoles oriented in the same direction.

A novel nanometric DNA thin film as a sensor for alpha radiation

The unexpected nuclear accidents have provided a challenge for scientists and engineers to develop sensitive detectors, especially for alpha radiation. Due to the high linear energy transfer value, sensors designed to detect such radiation require placement in close proximity to the radiation source. Here we report the morphological changes and optical responses of artificially designed DNA thin films in response to exposure to alpha radiation as observed by an atomic force microscope, a Raman and a reflectance spectroscopes. In addition, we discuss the feasibility of a DNA thin film as a radiation sensing material. The effect of alpha radiation exposure on the DNA thin film was evaluated as a function of distance from an 241Am source and exposure time. Significant reflected intensity changes of the exposed DNA thin film suggest that a thin film made of biomolecules can be one of promising candidates for the development of online radiation sensors.