Publications by authors named "Haiwon Lee"

51 Publications

Thickness-dependent humidity sensing by poly(vinyl alcohol) stabilized Au-Ag and Ag-Au core-shell bimetallic nanomorph resistors.

R Soc Open Sci 2018 Jun 6;5(6):171986. Epub 2018 Jun 6.

Institute of Nano Science and Technology, Hanyang University, Seoul 04763, South Korea.

We herein report a simple chemical route to prepare Au-Ag and Ag-Au core-shell bimetallic nanostructures by reduction of two kinds of noble metal ions in the presence of a water-soluble polymer such as poly(vinyl alcohol) (PVA). PVA was intentionally chosen as it can play a dual role of a supporting matrix as well as stabilizer. The simultaneous reduction of metal ions leads to an alloy type of structure. Ag(c)-Au(s) core-shell structures display tendency to form prismatic nanostructures in conjunction with nanocubes while Au(c)-Ag(s) core-shell structures show formation of merely nanocubes. Although UV-visible spectroscopy and X-ray photoelectron spectroscopy analyses of the samples typically suggest the formation of both Ag(c)-Au(s) and Au(c)-Ag(s) bimetallic nanostructures, the definitive evidence comes from high-resolution transmission electron microscopy-high-angle annular dark field elemental mapping in the case of Au(c)-Ag(s) nanomorphs only. The resultant nanocomposite materials are used to fabricate resistors on ceramic rods having two electrodes by drop casting technique. These resistors are examined for their relative humidity (RH) response in the range (2-93% RH) and both the bimetallic nanocomposite materials offer optimized sensitivity of about 20 Kohm/% RH and 300 ohm/% RH at low and higher humidity conditions, respectively, which is better than that of individual nanoparticles.
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http://dx.doi.org/10.1098/rsos.171986DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6030311PMC
June 2018

Fluorescence-based immunosensor using three-dimensional CNT network structure for sensitive and reproducible detection of oral squamous cell carcinoma biomarker.

Anal Chim Acta 2018 Oct 18;1027:101-108. Epub 2018 Apr 18.

Department of Chemistry, Hanyang University, Seoul, 04763, South Korea; Institute of Nano Science & Technology, Hanyang University, Seoul, 04763, South Korea. Electronic address:

A hierarchical three-dimensional network of carbon nanotubes on Si pillar substrate (3DN-CNTs) was developed for the accurate detection of oral squamous cell carcinoma (OSCC) in clinical saliva samples. The 3DN-CNTs were uniformly coated with a layer of aluminum oxides to enhance structural stability during biomarker detection. Cytokeratin-19 antigen (Cyfra 21-1) was utilized as a model biomarker of OSCC for fluorescence-based immunosensor using 3DN-CNTs (3DN-CNTs sensor). The 3DN-CNTs sensor enhances the sensitivity of Cyfra 21-1 detection by increasing the density of immobilized antibody through high surface area of 3DN-CNTs and enhancing the accessibility of biomolecules through the ordered pathway of hierarchical structure. The reliable detection limit for sensing of Cyfra 21-1 was estimated as in the level of 0.5 ng/mL and the quantitative estimation of Cyfra 21-1 was analyzed by 4-parameter logistic (4-PL) model for curve-fitting analysis. Clinical applicability of 3DN-CNTs sensor was evaluated through correlation with the commercially available electrochemiluminescence (ECL) detection system in the hospital. The assay results of the two systems for clinical saliva samples showed a good linear correlation. The 3DN-CNTs sensor offers great potential for accurate diagnosis of OSCC using Cyfra 21-1 biomarker in clinical fluids.
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http://dx.doi.org/10.1016/j.aca.2018.04.025DOI Listing
October 2018

Designing Ecofriendly Bionanocomposite Assembly with Improved Antimicrobial and Potent on-site Zika Virus Vector Larvicidal Activities with its Mode of Action.

Sci Rep 2017 Nov 14;7(1):15531. Epub 2017 Nov 14.

Institute of Nano Science and Technology, Hanyang University, Seoul, 04763, South Korea.

Dialyzed natural polymer, fibroin, from Bombyx mori was used to synthesize biocompatible silver and gold nanoparticles in-situ in dispersion form. The films of pure fibroin (PF), fibroin-silver nanocomposite (FSNC) and fibroin-gold nanocomposite (FGNC) were fabricated by drop casting method. The characterization of the resultant dispersion and films was performed by visual color change, UV-Vis spectroscopy and atomic force microscopy. The dispersions of PF, FSNC and FGNC were tested for antibacterial activity against E. coli NCIM 2065, S. aureus NCIM 5021, K. pneumoniae NCIM 2957, P. aeruginosa ATCC 9027 and antifungal activity against A. fumigatus NCIM 902. FSNC dispersion exhibited an effective antimicrobial action against all the tested microbes as compared to FGNC dispersion. The mechanism of action for FSNC and FGNC against these microorganisms is proposed. Additionally, the larvicidal activity of the films was investigated against the larvae of Aedes aegypti. The films of FSNC exhibited 100% mortality while the films of FGNC revealed 86-98% mortality against all the larval instars and pupae of A. aegypti. The phytotoxicity study of the nanocomposite films was also carried out to confirm the reusability of water. This is first noble metal nanocomposite based report on larvicidal activity of zika virus vector.
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http://dx.doi.org/10.1038/s41598-017-15537-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5686063PMC
November 2017

Swift tuning from spherical molybdenum microspheres to hierarchical molybdenum disulfide nanostructures by switching from solvothermal to hydrothermal synthesis route.

Nano Converg 2017 29;4(1):25. Epub 2017 Sep 29.

Institute of Nano Science and Technology, Hanyang University, Seoul, 04763 Republic of Korea.

Herein, we report the synthesis of metallic molybdenum microspheres and hierarchical MoS nanostructures by facile template-free solvothermal and hydrothermal approach, respectively. The morphological transition of the Mo microspheres to hierarchical MoS nanoflower architectures is observed to be accomplished with change in solvent from ethylenediamine to water. The resultant marigold flower-like MoS nanostructures are few layers thick with poor crystallinity while spherical ball-like molybdenum microspheres exhibit better crystalline nature. This is the first report pertaining to the synthesis of Mo microspheres and MoS nanoflowers without using any surfactant, template or substrate in hydro/solvothermal regime. It is opined that such nanoarchitectures of MoS are useful candidates for energy related applications such as hydrogen evolution reaction, Li ion battery and pseudocapacitors. Inquisitively, metallic Mo can potentially act as catalyst as well as fairly economical Surface Enhanced Raman Spectroscopy (SERS) substrate in biosensor applications.
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http://dx.doi.org/10.1186/s40580-017-0119-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5620365PMC
September 2017

A label-free electrochemical immunosensor for the detection of cardiac marker using graphene quantum dots (GQDs).

Biosens Bioelectron 2016 Dec 17;86:548-556. Epub 2016 Jul 17.

CSIR-Institute of Microbial Technology (CSIR-IMTECH), Sector 39, Chandigarh, 160038, India. Electronic address:

A label-free immunosensor based on electrochemical impedance spectroscopy has been developed for the sensitive detection of a cardiac biomarker myoglobin (cMyo). Hydrothermally synthesized graphene quantum dots (GQDs) have been used as an immobilized template on screen printed electrodes for the construction of an impedimetric sensor platform. The GQDs-modified electrode was conjugated with highly specific anti-myoglobin antibodies to develop the desired immunosensor. The values of charge transfer resistance (Rct) were monitored as a function of varying antigen concentration. The Rct value of the immunosensor showed a linear increase (from 0.20 to 0.31kΩ) in the range of 0.01-100ng/mL cMyo. The specific detection of cMyo was also made in the presence of other competing proteins. The limit of detection for the proposed immunosensor was estimated as 0.01ng/mL which is comparable to the standard ELISA techniques.
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http://dx.doi.org/10.1016/j.bios.2016.07.052DOI Listing
December 2016

Neuroprotective and antioxidant activities of bamboo salt soy sauce against HO-induced oxidative stress in rat cortical neurons.

Exp Ther Med 2016 Apr 9;11(4):1201-1210. Epub 2016 Feb 9.

Department of Neurology, College of Medicine, Hanyang University, Seoul 133791, Republic of Korea.

Bamboo salt (BS) and soy sauce (SS) are traditional foods in Asia, which contain antioxidants that have cytoprotective effects on the body. The majority of SS products contain high levels of common salt, consumption of which has been associated with numerous detrimental effects on the body. However, BS may be considered a healthier substitute to common salt. The present study hypothesized that SS made from BS, known as bamboo salt soy sauce (BSSS), may possess enhanced cytoprotective properties; this was evaluated using a hydrogen peroxide (HO)-induced neuronal cell death rat model. Rat neuronal cells were pretreated with various concentrations (0.001, 0.01, 0.1, 1 and 10%) of BSSS, traditional soy sauce (TRSS) and brewed soy sauce (BRSS), and were subsequently exposed to HO (100 µM). The viability of neuronal cells, and the occurrence of DNA fragmentation, was subsequently examined. Pretreatment of neuronal cells with TRSS and BRSS reduced cell viability in a concentration-dependent manner, whereas neuronal cells pretreated with BSSS exhibited increased cell viability, as compared with non-treated neuronal cells. Furthermore, neuronal cells pretreated with 0.01% BSSS exhibited the greatest increase in viability. Exposure of neuronal cells to HO significantly increased the levels of reactive oxygen species (ROS), B-cell lymphoma 2-associated X protein, poly (ADP-ribose), cleaved poly (ADP-ribose) polymerase, cytochrome , apoptosis-inducing factor, cleaved caspase-9 and cleaved caspase-3, in all cases. Pretreatment of neuronal cells with BSSS significantly reduced the levels of ROS generated by HO, and increased the levels of phosphorylated AKT and phosphorylated glycogen synthase kinase-3β. Furthermore, the observed effects of BSSS could be blocked by administration of 10 µM LY294002, a phosphatidylinositol 3-kinase inhibitor. The results of the present study suggested that BSSS may exert positive neuroprotective effects against HO-induced cell death by reducing oxidative stress, enhancing survival signaling, and inhibiting death signals.
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http://dx.doi.org/10.3892/etm.2016.3056DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4812428PMC
April 2016

A 3D networked polydiacetylene sensor for enhanced sensitivity.

Chem Commun (Camb) 2016 Jan;52(5):926-9

Department of Chemistry, Hanyang University, Seoul 133-791, Korea. and Institute of Nano Science and Technology, Hanyang University, Seoul 133-791, Korea.

A three order sensitivity enhancement over a 2D system was achieved with a polydiacetylene-immobilized 3D networked sensor matrix.
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http://dx.doi.org/10.1039/c5cc08566gDOI Listing
January 2016

Control over Neurite Directionality and Neurite Elongation on Anisotropic Micropillar Arrays.

Small 2016 Mar 23;12(9):1148-52. Epub 2015 Sep 23.

Center for Cell-Encapsulation Research, Department of Chemistry, KAIST, Daejeon, 305-701, South Korea.

Control over neurite orientation in primary hippocampal neurons is achieved by using interrupted, anisotropic micropillar arrays as a cell culture platform. Both neurite orientation and neurite length are controlled by a function of interpillar distance.
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http://dx.doi.org/10.1002/smll.201501896DOI Listing
March 2016

Enhanced Acid Diffusion Control by Using Photoacid Generator Bound Polymer Resist.

J Nanosci Nanotechnol 2015 Feb;15(2):1764-6

Photoacid generators (PAGs) have been widely used as a key component for improving photoresist performance. The acid diffusion influences on the photoresist characteristics of resolution and line edge roughness (LER). The PAG bound polymer resist has been a key component for solving the problems of PAG aggregation and acid diffusion control. A triphenyl sulfonium salt methacrylate as PAG was synthesized and copolymerized with crosslinkable glycidyl methacrylate and methyl methacrylate by radical reaction for a new PAG bound polymer resist. The characterization of resist polymers was carried out by 1H NMR. The lithographic performance of photoresists was investigated by ArF lithography. Both PAG bound resist and the PAG blended resist were employed to demonstrate the effect of PAG unit in a resist system. The polymer bound PAG resist improved the LER and showed a higher resolution than the PAG blend resist.
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http://dx.doi.org/10.1166/jnn.2015.9330DOI Listing
February 2015

Gold Nanowire Bundles Grown Radially Outward from Silicon Micropillars.

ACS Appl Mater Interfaces 2015 Aug 5;7(32):17582-6. Epub 2015 Aug 5.

†School of Chemical and Biomedical Engineering, Nanyang Technological University, 637457, Singapore.

One-dimensional (1D) micro- and nanostructures have become increasingly popular because of their tremendous prospect in various applications. While the design and fabrication of these structures from a single component in two-dimensional (2D) arrays is common, the attainment of hierarchical three-dimensional (3D) architectures made up of multicomponent one-dimensional structures is rare. Herein we report, for the first time, the lateral growth of gold nanowires from the sidewalls of substrate grown silicon micropillars to form a unique "wire-on-pillar" architecture. Unlike zero-dimensional (0D) point-like, 1D linear, and 2D planar Au structures, the obtained 3D "wire-on-pillar" Au architecture provides abundant hotspots between adjacent Au wires, which led to remarkably high surface-enhanced Raman scattering (SERS) signals.
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http://dx.doi.org/10.1021/acsami.5b05161DOI Listing
August 2015

Bio-inspired Hierarchical Nanowebs for Green Catalysis.

Small 2015 09 8;11(34):4292-7. Epub 2015 Jun 8.

Department of Chemistry, Hanyang University, 17 Haengdang dong, Seoul, 133-791, South Korea.

Bio-inspired 3D hierarchical nanowebs are fabricated using silicon micropillars, carbon nanotubes (CNT), and manganese oxide. The Si pillars act as artificial branches for growing CNTs and the secondary metal coating strengthens the structures. The simple but effective structure provides both chemical and mechanical stability to be used as a green catalyst for recycling waste polymers into raw materials.
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http://dx.doi.org/10.1002/smll.201403717DOI Listing
September 2015

Elucidating how bamboo salt interacts with supported lipid membranes: influence of alkalinity on membrane fluidity.

Eur Biophys J 2015 Jul 24;44(5):383-91. Epub 2015 May 24.

Department of Convergence Nanoscience, College of Natural Science, Hanyang University, Seoul, 133070, Korea.

Bamboo salt is a traditional medicine produced from sea salt. It is widely used in Oriental medicine and is an alkalizing agent with reported antiinflammatory, antimicrobial and chemotherapeutic properties. Notwithstanding, linking specific molecular mechanisms with these properties has been challenging to establish in biological systems. In part, this issue may be related to bamboo salt eliciting nonspecific effects on components found within these systems. Herein, we investigated the effects of bamboo salt solution on supported lipid bilayers as a model system to characterize the interaction between lipid membranes and bamboo salt. The atomic composition of unprocessed and processed bamboo salts was first analyzed by mass spectrometry, and we identified several elements that have not been previously reported in other bamboo salt preparations. The alkalinity of hydrated samples was also measured and determined to be between pH 10 and 11 for bamboo salts. The effect of processed bamboo salt solutions on the fluidic properties of a supported lipid bilayer on glass was next investigated by fluorescence recovery after photobleaching (FRAP) analysis. It was demonstrated that, with increasing ionic strength of the bamboo salt solution, the fluidity of a lipid bilayer increased. On the contrary, increasing the ionic strength of near-neutral buffer solutions with sodium chloride salt diminished fluidity. To reconcile these two observations, we identified that solution alkalinity is critical for the effects of bamboo salt on membrane fluidity, as confirmed using three additional commercial bamboo salt preparations. Extended-DLVO model calculations support that the effects of bamboo salt on lipid membranes are due to the alkalinity imparting a stronger hydration force. Collectively, the results of this work demonstrate that processing of bamboo salt strongly affects its atomic composition and that the alkalinity of bamboo salt solutions contributes to its effect on membrane fluidity.
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http://dx.doi.org/10.1007/s00249-015-1043-8DOI Listing
July 2015

The effect of hydrophilic photoacid generator on acid diffusion in chemical amplification resists.

J Nanosci Nanotechnol 2014 Dec;14(12):9662-4

A photoacid generator (PAG) is a component of chemical amplification photoresists (CAR). The most widely used PAG in CAR system is triphenyl onium salt which is well known to one of the best leaving groups from various radiation. Acid diffusion influences resist characteristics in area such as resolution and linewidth control. The structure of the hydrophilic PAG was designed to restrict acid diffusion within the photoresist. Acid amplification was suppressed by the hydroxyl group-acid interaction. Novel PAGs with functional groups were synthesized and characterized. Poly(GMA-co-MMA) was synthesized with a combination of crosslinkable glycidyl methacrylate (GMA) and highly refractive methyl methacrylate (MMA). The synthesized polymers were confirmed by NMR and FT-IR, and their thermal properties were studied using TGA and DSC. The resists were evaluated as a positive type resist for ArF lithography. PAGs exhibited good acid generation efficiency with controlled acid diffusion. We found that the energy latitude property of the photoresist was improved with hydroxyl-PAG.
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http://dx.doi.org/10.1166/jnn.2014.10155DOI Listing
December 2014

TiO2 particles on a 3D network of single-walled nanotubes for NH3 gas sensors.

J Nanosci Nanotechnol 2014 Dec;14(12):9148-51

Ammonia (NH3) gas is one of the gases which causes damage to environment such as acidification and climate change. In this study, a gas sensor based on the three-dimensional (3D) network of single-walled nanotubes (SWNTs) was fabricated for the detection of NH3 gas in dry air. The sensor showed enhanced performance due to the fast gas diffusion rate and weak interactions between the carbon nanotubes and the substrate. Metal oxide particles were introduced to enhance the performance of the gas sensor. Atomic layer deposition (ALD) was employed to deposit the metal oxide in the complex structure, and good control over thickness was achieved. The hybrid gas sensor consisting of the 3D network of SWNTs with anatase TiO2 particles showed stable, repeatable, and enhanced gas sensor performance. The phase of TiO2 particles was characterized by Raman and the morphology of the TiO2 particles on the 3D network of SWNTs was analyzed by transmission electron microscope.
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http://dx.doi.org/10.1166/jnn.2014.10092DOI Listing
December 2014

Synthesis of triphenylsulfonium triflate bound copolymer for electron beam lithography.

J Nanosci Nanotechnol 2014 Aug;14(8):6270-3

Photoacid generator (PAG) has been widely used as a key component in photoresist for high-resolution patterning with high sensitivity. A novel acrylic monomer, triphenylsulfonium salt methyl methacrylate (TPSMA), was synthesized and includes triphenylsulfonium triflate as a PAG. The poly(MMA-co-TPSMA) (PMT) as a polymer-bound PAG was synthesized with methyl methacrylate (MMA) and TPSMA for electron beam lithography. Characterization of PMT was carried out by NMR and FTIR. The molecular weight was analyzed by GPC. Thermal properties were studied using TGA and DSC. Thecharacterization results were in good agreement with corresponding chemical compositions and thermal stability. PMT was subsequently employed in electron beam lithography and its lithographic performance was confirmed by FE-SEM. This PMT was accomplished to improve the lithographic performance including sensitivity, line width roughness (LWR) and resolution. We found that PMT was capable of 20 nm negative tone patterns with better sensitivity than hydrogensilsesquioxane (HSQ) which is a conventional negative tone resist.
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http://dx.doi.org/10.1166/jnn.2014.8826DOI Listing
August 2014

A Highly Sensitive and Reliable Strain Sensor Using a Hierarchical 3D and Ordered Network of Carbon Nanotubes.

Small 2015 Jul 26;11(25):2990-4. Epub 2015 Feb 26.

Department of Chemistry, Hanyang University, Seoul, 133-791, South Korea.

A 3D network of single-walled carbon nanotubes embedded in poly-(dimethylsiloxane) is presented as a promising route to the fabrication of a flexible film with ordered and interconnected single-walled carbon nanotubes. This is possible using a simple transfer method of as-grown hierarchical single-walled carbon nanotubes on a Si pillar substrate. This film is used as a highly sensitive strain gauge sensor. This type of network embedded in a polymer film should be applicable to many fields involving mechanically stable and reliable strain sensors.
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http://dx.doi.org/10.1002/smll.201401812DOI Listing
July 2015

Contribution of temperature to deformation of adsorbed vesicles studied by nanoplasmonic biosensing.

Langmuir 2015 Jan 7;31(2):771-81. Epub 2015 Jan 7.

School of Materials Science and Engineering, Nanyang Technological University , 50 Nanyang Avenue 639798, Singapore.

With increasing temperature, biological macromolecules and nanometer-sized aggregates typically undergo complex and poorly understood reconfigurations, especially in the adsorbed state. Herein, we demonstrate the strong potential of using localized surface plasmon resonance (LSPR) sensors to address challenging questions related to this topic. By employing an LSPR-based gold nanodisk array platform, we have studied the adsorption of sub-100-nm diameter 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid vesicles on titanium oxide at two temperatures, 23 and 50 °C. Inside this temperature range, DPPC lipid vesicles undergo the gel-to-fluid phase transition accompanied by membrane area expansion, while DOPC lipid vesicles remain in the fluid-phase state. To interpret the corresponding measurement results, we have derived general equations describing the effect of deformation of adsorbed vesicles on the LSPR signal. At the two temperatures, the shape of adsorbed DPPC lipid vesicles on titanium oxide remains nearly equivalent, while DOPC lipid vesicles become less deformed at higher temperature. Adsorption and rupture of DPPC lipid vesicles on silicon oxide were also studied for comparison. In contrast to the results obtained on titanium oxide, adsorbed vesicles on silicon oxide become more deformed at higher temperature. Collectively, the findings demonstrate that increasing temperature may ultimately promote, hinder, or have negligible effect on the deformation of adsorbed vesicles. The physics behind these observations is discussed, and helps to clarify the interplay of various, often hidden, factors involved in adsorption of biological macromolecules at interfaces.
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http://dx.doi.org/10.1021/la504267gDOI Listing
January 2015

Fabrication of cobalt magnetic nanostructures using atomic force microscope lithography.

J Nanosci Nanotechnol 2013 Dec;13(12):8055-8

Department of Chemistry, Hanyang University, 17 Haengdang dong, Seoul 133-791, Korea.

Cobalt nanopatterns are promising assemblies for patterned magnetic storage applications. The fabrication of cobalt magnetic nanostructures on n-tridecylamine x hydrochloride (TDA x HCl) self-assembled monolayer (SAM) modified silicon surfaces using direct writing atomic force microscope (AFM) lithography for localized electrochemical reduction of cobalt ions was demonstrated. The ions were reduced to form metal nanowires along the direction of the electricfield between the AFM tip and the substrate. In this lithography process, TDA x HCI SAMs play an important role in the lithography process for improving the resolution of cobalt nanopatterns by preventing nonspecific reduction of cobalt ions on the unwritten background. Cobalt nanowires and nanodots with width of 225 +/- 26 nm and diameter of 208 +/- 28 nm were successfully fabricated. Platinium-coated polydimethylsiloxane (PDMS) stamp was used fabricating bulk cobalt structures which can be detected by energy dispersive X-ray spectroscopy for element analysis and the physical and magnetic properties of these cobalt nanopatterns were characterized using AFM and magnetic force microscope.
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http://dx.doi.org/10.1166/jnn.2013.8173DOI Listing
December 2013

Growth, solvent effects, and thermal desorption behavior of octylthiocyanate self-assembled monolayers on Au(111).

Phys Chem Chem Phys 2013 Mar 4;15(10):3609-17. Epub 2013 Feb 4.

Institute of Nano Science and Technology, Hanyang University, Seoul, Korea.

The growth process, solvent effects, and thermal desorption behavior of octylthiocyanate [OTC, CH(3)(CH(2))(7)S-CN] self-assembled monolayers (SAMs) on Au(111) were characterized by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS). To investigate their growth processes, octanethiol [OT, CH(3)(CH(2))(7)S-H] and OTC SAMs were prepared in 0.5 μM ethanol solution at room temperature as a function of immersion time: 10 min, 1 h, 2 h, and 24 h. STM imaging revealed that OT SAMs underwent a phase transition from the liquid phase containing striped-phase domains to the closely packed c(4 × 2) phase. OTC SAMs underwent a different phase transition from the liquid phase containing aggregated molecules to the disordered phase containing striped-phase domains. The adsorption amounts of OTC SAMs formed after immersion for 10 min and 24 h were measured to be 16% and 30% smaller than those of OT SAMs under the same conditions. STM and XPS results show that the growth kinetics of OTC SAMs on Au(111) are much slower than those of OT SAMs. Hexane resulted in OTC SAMs of higher structural quality than ethanol, DMF, or toluene. TDS measurements revealed that the relative desorption intensities of octanethiolate (C8S(+), monomer) and dioctyl disulfide (C8SSC8(+), dimer) to octanethiol (C8SH(+)) fragments for OTC SAMs were much weaker than those of OT SAMs. This is because desorption of monomers and dimers is strongly suppressed by low surface coverage of OTC SAMs, as revealed by STM observations.
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http://dx.doi.org/10.1039/c3cp44425bDOI Listing
March 2013

Synthesis of novel photoacid generator containing resist polymer for electron beam lithography.

J Nanosci Nanotechnol 2012 Jan;12(1):725-9

Department of Chemistry Hanyang University, Seoul 133-791, Korea.

Photoacid generators (PAGs) have been widely used as a key material in the development of novel photoresist materials. One of the important uses of PAGs is found in chemically amplified photoresists (CARs) because of their high photosensitivity and high resolution capability. Triphenylsulfonium salt methacrylate (TPSMA) as the PAG has been bounded in the main polymer backbone. TPSMA was employed for synthesis of terpolymers, poly(MMA-co-tBVPC-co-TPSMA) and poly(tBVPC-co-tBOCPOMI-co-TPSMA) as a positive tone photoresists by free radical polymerization using AIBN. Terpolymers with various ratio of TPSMA, MMA, tBVPC and tBOCOPMI were synthesized and well characterized by FTIR, NMR. Molecular weight distribution was analyzed by GPC. Thermal properties were studied using TGA, DSC which showed thermal stability of terpolymer up to 150 degrees C. We have applied E-beam lithography and KrF lithography in order to demonstrate the effect of the polymer bounded PAG resists. These positive tone resists were successfully applied for fabrication of nano-scale patterns.
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http://dx.doi.org/10.1166/jnn.2012.5344DOI Listing
January 2012

Hierarchical and multifunctional three-dimensional network of carbon nanotubes for microfluidic applications.

Adv Mater 2012 Apr 16;24(15):1975-9. Epub 2012 Mar 16.

Department of Chemistry, Hanyang University, Seoul 133-791, Korea.

Three-Dimensional network of carbon nanotubes: The 3D network of CNTs have hierarchical structures comprised of interconnected SWNTs between Si pillars in microfluidic channels. The Al(2)O(3) coated 3D networks were used for size different nanoparticles filtration and streptavidin capturing in very diluted solution. The 3D network of SWNTs systems will provide a robust multifuncitonal platform for a variety of biomedical and environmental applications.
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http://dx.doi.org/10.1002/adma.201104958DOI Listing
April 2012

Modification of silicon substrate using low-energy proton beam for selective growth of CNTs.

J Nanosci Nanotechnol 2011 May;11(5):4378-83

Department of Chemistry, Hanyang University, Seoul 133-791, Korea.

A 3 keV low-energy proton beam was used to irradiate a silicon substrate for selective modification. The water contact angle measurement, chemical etching test with HF and the auger electron spectroscopy were used to investigate the chemical properties and the material composition of the proton beam-irradiated silicon substrate. The proton beam-irradiated silicon substrate was covered with a silicon oxide layer of about 60-70 angstroms due to the incorporation of oxygen molecules after exposure to ambient air. The silicon oxide layer produced by the proton beam was highly resistant to HF treatment which typically used to remove the silicon oxide on a substrate, and the surface of it was more hydrophilic than the native silicon oxide removed silicon surface with Si-H surface group. For the selective growth of carbon nanotubes (CNTs), the silicon oxide pattern was easily fabricated via proton beam irradiation when the silicon substrate was covered with a shadow mask. The Fe-Mo bimetallic catalysts for the growth of CNTs were adsorbed onto the silicon oxide layer, which is more hydrophilic than the silicon surface. The CNTs were grown on the patterned substrate using a chemical vapor deposition method, and it was confirmed by scanning electron microscopy.
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http://dx.doi.org/10.1166/jnn.2011.3712DOI Listing
May 2011

Biophysical characterization of the molecular orientation of an antibody-immobilized layer using secondary ion mass spectrometry.

Analyst 2011 Apr 15;136(7):1412-9. Epub 2011 Feb 15.

Program for Bio-Microsystem Technology, Korea University, 1, 5-ka, Anam-dong, Seongbuk-Gu, Seoul, 136-701, Republic of Korea.

The molecular orientation of antibody layers formed on separate solid matrices (e.g., gold-coated glass substrate) was characterized by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS) in static mode. For comparison, three different antibody species, IgG, F(ab')(2), and Fab, were prepared, biotinylated in random and site-directed fashions, and immobilized on distinct streptavidin-coated surfaces. ToF-SIMS analyses of each antibody layer revealed that the secondary ion intensity peaks measured at the mass-to-charge (m/z) ratio 253, 325, and 647 were unique to the site-directly immobilized antibodies. The ions in the three peaks were detected neither from the streptavidin layer nor from the randomly prepared antibody, indicating that the insolubilized antibody layers constructed in the two different manners had distinct molecular arrangements. The antibody preparations were further tested for their binding characteristics in sandwich-type immunoassays, which showed that the site-directed antibodies consistently enhanced the detection capability comparing to those randomly prepared. Based on the analytical results of both the ToF-SIMS analysis and sandwich-type immunoassays, the site-directed antibody species were immobilized on the surfaces in a more orientated manner, with their antigen binding sites exposed to the bulk solution, than when random immobilization was used.
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http://dx.doi.org/10.1039/c0an00672fDOI Listing
April 2011

Electrical impedance properties of carbon nanotube composite electrodes for chemical and biosensor.

J Nanosci Nanotechnol 2010 May;10(5):3449-52

Nanotechnology Information Analysis Team, Korea Institute of Science and Technology Information, Seoul 130-741, Korea.

Electrical impedance properties of different type of carbon nanotubes based bulk electrodes have been investigated to develop chemical and biosensors. The bulk composite electrodes were fabricated with single-wall and multi-wall carbon nanotubes involving ionic conducting host polymer, Nafion, by using traditional solution-casting techniques. Under the various amounts of buffer solution, resistance and capacitance of the electrodes were measured with LCR meter and their characteristics due to ionic conducting host polymer were investigated by means of electrokinetic analysis. The capacitance values showed drastic change while the resistances only changed within few percent ranges. Electrical impedance measurement provided rapid and simple sensing mechanism to develop chemical sensor and biosensors with bulk nano electrodes.
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http://dx.doi.org/10.1166/jnn.2010.2338DOI Listing
May 2010

Real-time atomic force microscopy in lubrication condition.

Ultramicroscopy 2010 Jun 6;110(7):826-30. Epub 2010 Mar 6.

Faculty of Nanotechnology and Advanced Material Engineering, Sejong University, Seoul 143-747, South Korea.

We have studied frictional force and wear problem in real-time atomic force microscopy in contact-mode using a resonator type mechanical scanner allegedly reported. The fast scanning may cause wear in the sample surface or the tip, and may deteriorate the image quality. Mineral oil was used to make a lubricious surface on a polycarbonate sample, and it was found that the interfacial frictional force was decreased. A Si tip which was coated with a hydrophobic film by means of chemical modification was confirmed to diminish the frictional force in the fast scanning process. The resultant image quality was improved due to reduced friction and wear.
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http://dx.doi.org/10.1016/j.ultramic.2010.02.045DOI Listing
June 2010

Direct nanofabrication of copper on silicon substrate by electrochemical atomic force microscope lithography.

J Nanosci Nanotechnol 2009 Dec;9(12):7076-9

Department of Nanoscale Semiconductor Engineering, Hanyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea.

The electrochemical reaction by applying an electrical bias between an atomic force microscope (AFM) tip and a substrate was used to directly fabricate desired copper patterns. The negative sample bias could strongly reduce copper at the point localized by an AFM tip but not oxidize silicon. The mixture solution of Cu(NO3)2 and poly(sodium 4-styrenesulfonate) which are highly soluble in water was used to form a conductive copper ion film. The arrayed dots and line patterns were fabricated by electrical exposure at regular steps and continuous bias, respectively. This technique demonstrated the fabrication of copper patterns by using the electrochemical reduction by AFM lithography.
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December 2009

Fabrication of ball-shaped atomic force microscope tips by ion-beam-induced deposition of platinum on multiwall carbon nanotubes.

Ultramicroscopy 2009 Dec 30;110(1):82-8. Epub 2009 Sep 30.

Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea.

Ball-shaped atomic force microscope (AFM) tips (ball tips) are useful in AFM metrology, particularly in critical dimension AFM metrology and in micro-tribology. However, a systematic fabrication method for nano-scale ball tips has not been reported. We report that nano-scale ball tips can be fabricated by ion-beam-induced deposition (IBID) of Pt at the free end of multiwall carbon nanotubes that are attached to AFM tips. Scanning electron microscopy and transmission electron microscopy analyses were done on the Pt ball tips produced by IBID in this manner, using ranges of Ga ion beam conditions. The Pt ball tips produced consisted of aggregated Pt nano-particles and were found to be strong enough for AFM imaging.
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http://dx.doi.org/10.1016/j.ultramic.2009.09.011DOI Listing
December 2009

Automatic approaching method for atomic force microscope using a Gaussian laser beam.

Rev Sci Instrum 2009 Jul;80(7):073705

Division of Electrical and Computer Engineering, Hanyang University, Seoul 133-791, Republic of Korea.

In this paper, a criterion for a fast automatic approach method in conventional atomic force microscope is introduced. There are currently two approach methods: automatic and semiautomatic methods. However, neither of them provides a high approach speed to enable the avoidance of possible damage to tips or samples. Industrial atomic force microscope requires a high approach speed and good repeatability for inspecting a large volume. Recently, a rapid automatic engagement method was reported to improve the approach speed. However, there was no information on how to determine the safe distance. This lack of information increases the chance for damage to occur in calibrating optimal approach speed. In this paper, we show that the proposed criterion can be used for decision making in determining mode transitions from fast motion to slow motion. The criterion is calculated based on the average intensity of a Gaussian laser beam. The tip-sample distance where the average intensity becomes the maximum value is used for the criterion. We explain the effects of the beam spot size and the window size on the average intensity. From experimental results with an optical head used in a commercial atomic force microscope, we observed that the mean and standard deviation (of the distance at which intensity is the maximum for the 25 experiments) are 194.0 and 15.0 microm, respectively, for a rectangular cantilever (or 224.8 and 12.6 microm for a triangular cantilever). Numerical simulation and experimental results are in good agreement.
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http://dx.doi.org/10.1063/1.3181787DOI Listing
July 2009

The fabrication of polyaniline/single-walled carbon nanotube fibers containing a highly-oriented filler.

Nanotechnology 2009 Feb 3;20(8):085701. Epub 2009 Feb 3.

Center for Bio-Artificial Muscle and Department of Biomedical Engineering, Hanyang University, Seoul 133-791, Korea.

Highly uniform composite nanofibers composed of well-oriented single-walled carbon nanotubes (SWCNTs) wrapped in a conducting polymer have been fabricated using electrospinning. Water-soluble polyaniline (WS-PANI) was used as a conducting material to improve the processability during electrospinning. The WS-PANI formed a homogeneous dispersion with the SWCNTs and poly(vinyl alcohol), and good compatibility of the WS-PANI with the SWCNTs was demonstrated by data showing interactions between two components and the wrapping of the SWCNTs by the WS-PANI. Through transmission electron microscopy, atomic force microscopy, and polarized Raman spectroscopy, we confirmed that the WS-PANI plays an important role as a conducting polymer matrix to achieve aligned SWCNTs in composite nanofibers and to form uniform nanofibers.
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http://dx.doi.org/10.1088/0957-4484/20/8/085701DOI Listing
February 2009

Selective immobilization of proteins on gold dot arrays and characterization using chemical force microscopy.

J Colloid Interface Sci 2009 Jun 8;334(2):161-6. Epub 2009 Apr 8.

Department of Chemistry, Hanyang University, Seoul 133-791, Republic of Korea.

Streptavidin that has four binding sites arranged in two opposing pairs is known as one of the most important linker proteins for binding the second biotinylated protein. To efficiently locate streptavidins to selective positions without nonspecific binding, we prepared well-controlled arrays of biotins on a gold surface by using a mixed self-assembly process. Two thiol derivatives (11-mercapto-1-undecanol and 11-mercaptoundecanoic-(8-biotinylamido-3,6-dioxaoctyl)amide) were used for preparing the mixed self-assembled monolayers. Fragment antibodies modified with biotin were immobilized on a gold surface covered with streptavidin. This system was applied to gold dot arrays formed by nanosphere lithography. The gold dot arrays were used as the mother structure to construct the array of proteins at the nanometer scale. Selective immobilization of antibodies was characterized by imaging the substrate with an atomic force microscope and measuring the interaction force between biomaterials by chemical force microscopy. Also, the interaction force between antibodies was compared with the force predicted using the Johnson-Kendall-Roberts theory.
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http://dx.doi.org/10.1016/j.jcis.2009.03.082DOI Listing
June 2009