Kook-Nyung Lee

Fabrication of Suspended Silicon Nanowire Arrays

A method to fabricate suspended silicon nanowires that are applicable to electronic and electromechanical nanowire devices is reported. The method allows for the wafer-level production of suspended silicon nanowires using anisotropic etching and thermal oxidation of single-crystal silicon. The deviation in width of the silicon nanowire bridges produced using the proposed method is evaluated. The NW field-effect transistor (FET) properties of the device obtained by transferring suspended nanowires are shown to be practical for useful functions.

Protein patterning by maskless photolithography on hydrophilic polymer-grafted surface.

With the help of a microfabrication process and surface modification technology, a method of fabricating protein patterned chips was developed which can be utilized as a powerful tool for performing bioassays in a high-throughput manner. A digital micromirror array (MMA) system was used as a virtual photomask, so that a maskless photolithography process was able to be used to build patterned biomolecules on a chip by selective illumination onto the chip surface. We utilized the nitroveratryloxycarbonyl (NVOC) group as a photolabile protecting group for protein patterning. The NVOC-protected surface was selectively irradiated by a UV illuminator using an MMA. After removing the NVOC group, biotin was coupled to the NVOC-cleaved site, onto which a buffered streptavidin solution was eluted. At this point, we could obtain a streptavidin-patterned surface and observe the effect of the polymer-grafted surface in reducing nonspecific binding.

Effects of surface modification on the resin-transfer moulding (RTM) of glass-fibre/unsaturated-polyester composites

Abstract The effects of glass fibre surface modification on the flow characteristics of unsaturated polyester (UPE) resin were investigated in the resin-transfer moulding (RTM) process. γ-Methacryloxypropyl trimethoxy silane (γ-MPS) was used as a glass fibre surface modifier. It was found that surface energy of glass fibre was decreased by γ-MPS treatment by advancing contact-angle measurement. Unsteady state permeability of glass fabric preforms was measured according to Darcys law. The apparent permeability of γ-MPS-treated glass fabric preforms was slightly lower than that of untreated fabric performs because of the macro/micro flow induced by capillary action. The void contents and the flexural properties of the cured glass-fibre/UPE composites were estimated and morphological study of the glass-fibre/UPE composites was also performed by SEM. When the fibre surface was treated with γ-MPS, the void content and the flexural properties of the glass-fibre/UPE composites were different in different regions of the mould cavity.

Chiral separation of gemifloxacin in sodium‐ containing media using chiral crown ether as a chiral selector by capillary and microchip electrophoresis

Chiral crown ether, (+)‐(18‐crown‐6)‐tetracarboxylic acid (18C6H4), is an effective chiral selector for resolving enantiomeric primary amines owing to the difference in affinities between 18C6H4 and each of the amine enantiomers. In addition to the destacking effect of sodium ion in the sample solution, the strong affinity of sodium ion to the polyether ring of crown ether is unfavorable to chiral capillary electrophoresis using 18C6H4 as a chiral selector. In this report, the chiral separation of gemifloxacin dissolved in a saline sample matrix using 18C6H4 was investigated. Adding a chelating agent, ethylenediaminetetraacetic acid (EDTA), to the run buffer greatly improved the separation efficiencies and peak shapes. The successful chiral separation of gemifloxacin in a urinary solution was demonstrated for both capillary and microchip electrophoresis.

Well controlled assembly of silicon nanowires by nanowire transfer method

Efforts to date in silicon nanowire research have primarily focused on the nanowire synthesis and the demonstration of individual nanowire-based devices exhibiting interdisciplinary potential spanned from electrical (Duan et al 2003 Nature 425 274?8; Cui and Lieber 2001 Science 291 851?3; Morales and Lieber 1998 Science 279 208?11) through biomedical applications (Cui et al 2003 Science 293 1289?92; Zheng et al 2005 Nature Biotechnol. 23 1294?301). However, the realization of integrated nanowire devices requires well ordered assembly of a silicon nanowire (Huang et al 2001 Science 291 630?3; Whang et al 2003 Nano Lett. 3 1255?9) as well as simple and cost effective fabrication. Here we describe a simple fabrication scheme and a large-scale assembly of silicon nanowires by combining top-down fabrication with nanowire transfer onto another insulator substrate for device manufacture. Our innovative fabrication method enables us to obtain well defined silicon nanowires as a freestanding bridge structure with a diameter of 20?200?nm and a length varying from 5 to 100??m using micro-machining processes. Direct transfer of the freestanding nanowires simply provides large-scale assembly of silicon nanowire on various substrates for highly integrated devices such as high-performance thin-film transistors (TFTs) (Duan et al 2003 Nature 425 274?8; Ishihara et al 2003 Thin Solid Films 427 77?85) and nanowire-based electronics (Cui and Lieber 2001 Science 291 851?3). Electrical transport properties of the transferred silicon nanowire were also investigated.

Protein patterning by virtual mask photolithography using a micromirror array

The successful development of biosensors and protein chips requires a method for protein patterning on a solid surface. We describe a virtual mask photolithography method for the surface patterning of proteins on a chip using a micromirror array (MMA) and its characterization. The excitation light was switched on or off using the MMA, and the light pattern was transferred using the pattern of switched-on mirrors. The nitroveratryloxycarbonyl (NVOC) group was utilized as a photolabile protecting group for protein patterning, so that biomolecules could be immobilized on a patterned substrate. When illuminated by UV light, the photolabile protecting group was removed by a chemical reaction, and non-illuminated photolabile protecting groups protected the chip surface. Biotin was coupled only to the region where the protecting group had been removed, and so, biotin?streptavidin patterns were obtained. A two-dimensional MMA was designed and fabricated using micromachining technology for use as a spatial light modulator. The projection system consisted of the MMA, a light source and other optical components, such as a projection lens. Fluorescein isothiocyanate was used to visualize the NVOC photo-cleavage sites and the biotin?streptavidin reaction. Parallel and quantitative experiments required in the development of surface modification technology for protein immobilization on a surface can easily be performed using this protein patterning system.

Micromirror array for protein micro array fabrication

We have designed, fabricated and characterized a micromirror array for protein microarray fabrication that has a simple structure, and the straightforward fabrication process for the mirror will allow the use of low-cost mirrors in protein pattern applications. The characteristics of an exposure system utilizing the micromirror array have been demonstrated by means of an experiment employing a photoresist that is in general use in the semiconductor industry. The micromirror dimensions were 54 × 54 μm2, with a 30 μm separation between mirrors, and a 5.5 μm gap from the bottom electrode so that the mirror had an approximately 10° deflection angle. The size and separation of the mirror were designed in consideration of the protein pattern size and pitch, in contrast with the commercial Texas Instruments Digital Light Processor, which is utilized in the components of projection display systems. The exposure system combined with the micromirror has been used in the photochemical synthesis of chemical ligands via protein immobilization on a chip. Several photosynthesis experiments for peptide array synthesis have been carried out using the micromirror array. Parallel experiments on photochemical ligand synthesis on a chip can easily be performed in the laboratory using this exposure system.

Automated Maskless Photolithography System for Peptide Microarray Synthesis on a Chip

Maskless photolithographic peptide synthesis was performed on a glass chip using an automated peptide array synthesizer system. The peptide array synthesizer was built in a closed box, which contained optical and fluidic systems. The conditions for peptide synthesis were fully controlled by a computer program. For the peptide synthesis on a glass chip, 20 NVOC-protected amino acids were synthesized. The coupling efficiencies of two model peptide sequences were examined on ACA/APTS and PEG/CHI/GPTS chips. PEG/CHI/GPTS chip gave higher average stepwise yields of GIYWHHY (94%) and YIYGSFK (98%) than those of ACA/APTS chip. To quantify peptide-protein binding affinity, HPQ- or HPM-containing pentapeptides were synthesized on a PEG/CHI/GPTS chip and the binding event of Cy3 labeled-streptavidin was quantified. The peptide sequence of IQHPQ showed highest binding affinity with Cy3 labeled-streptavidin. The results demonstrated that the photolithographic peptide array synthesis method efficiently quantified the binding activities of protein-peptide interactions and it can be used for additional biological assay applications.

Improvement of Maskless Photolithography of Bio Pattern with Single Crystalline Silicon Micromirror Array

This study focuses on the enhancement of maskless photolithography as well as the peptide synthesis application with single crystalline silicon micromirrors. A single crystalline silicon micromirror array has been designed and fabricated in order to improve its application to the peptide synthesis. A micromirror rotates about ± 9° at the pull-in voltage, which can range from 90.7 V to 115.1 V. A 210㎛-by-210 ㎛ micromirror device with 270 ㎛ mirror pitch meets the requirements of an adequately precise separation for peptide synthesis. Synthetic 16 by 16 peptide array corresponds to the same number of micromirrors. The large size of peptide pattern and the separation facilitate biochip experiments using fluorescence assay. The peptide pattern has been synthesized on the GPTS-PEG200 surface with BSA-blocking and thereupon the background was acetylated to reject non-specific bindings. Hence, an averaged slope at the pattern edge has been distinguishably improved in comparison to patterning results from an aluminum micromirror.

A sensitive electrochemical sensor for in vitro detection of parathyroid hormone based on a MoS2-graphene composite

This paper reports a biosensor based on a MoS2-graphene (MG) composite that can measure the parathyroid hormone (PTH) concentration in serum samples from patients. The interaction between PTH and MG was analysed via an electrochemical sensing technique. The MG was functionalized using l-cysteine. Following this, PTH could be covalently immobilized on the MG sensing electrode. The properties of MG were evaluated using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectrometry. Following optimization of immobilized materials—such as MG, PTH, and alkaline phosphatase (ALP)—the performance of the MG sensor was investigated via cyclic voltammetry, to assess its linearity, repeatability, and reproducibility. Electrochemical impedance spectroscopy was performed on graphene oxide (GO) and MG-modified electrodes to confirm the capture of a monoclonal antibody (MAb) targeting PTH. Furthermore, the ALP-PTH-MG sensor exhibits a linear response towards PTH from artificial serum over a range of 1–50 pg mL−1. Moreover, patient sera (n = 30) were evaluated using the ALP-PTH-MG sensor and compared using standard equipment (Roche E 170). The P-value is less than 0.01 when evaluated with a t-test using Welch’s correction. This implies that the fabricated sensor can be deployed for medical diagnosis.