Younggeun Park

Selective and sensitive detection of metal ions by plasmonic resonance energy transfer-based nanospectroscopy

Highly selective and sensitive optical methods for the detection of metal ions have had a substantial impact on molecular biology, environmental monitoring and other areas of research. Here we demonstrate a new method for detecting metal ions that is based on selective plasmonic resonance energy transfer (PRET) between conjugated metal-ligand complexes and a single gold nanoplasmonic probe. In addition to offering high spatial resolution due to the small size of the probe, our method is 100 to 1,000 times more sensitive than organic reporter-based methods. Moreover, it can achieve high selectivity owing to the selective formation of Cu(2+) complexes and selective resonant quenching of the gold nanoplasmonic probe by the conjugated complexes. We expect that PRET-based metal ion sensing could have applications in cellular imaging, systems biology and environmental monitoring.

Light-extraction enhancement of vertical-injection GaN-based light-emitting diodes fabricated with highly integrated surface textures

We report on the fabrication of high-efficiency vertical-injection GaN-based light-emitting diodes (LEDs) fabricated with integrated surface textures. An optical ray-tracing simulation shows that the high integration of surface textures can effectively enhance the light-extraction efficiency. The integrated surface textures are fabricated on the top surface of LEDs by generating hexagonal cones on the periodically corrugated surfaces of n-GaN. Compared to reference LEDs without textures, LEDs fabricated with integrated surface textures show an enhancement of the output power by a factor of 2.59, which is in agreement with the calculated results.

Synthesis and characterization of mesoporous alumina as a catalyst support for hydrodechlorination of 1,2-dichloropropane: Effect of catalyst preparation method

A mesoporous alumina was synthesized by a posthydrolysis method. The prepared mesoporous alumina was found to have randomly ordered pores, and retained relatively high surface area with narrow pore size distribution centered at ca. 4 nm. Nickel precursors were then supported on the mesoporous alumina by an impregnation (Ni-IMP) and vapor deposition (Ni-VD) method. Several characterizations were carried out in order to investigate physical and chemical properties of mesoporous alumina and supported Ni catalysts. TPR, XPS, and UV-DRS measurements revealed that the Ni-IMP catalyst retained much more amounts of surface nickel aluminate-like species than the Ni-VD sample. TPD experiments also showed that nickel aluminate species affected the adsorption amounts of reactant (1,2-dichloropropane). In the hydrodechlorination of 1,2-dichloropropane (DCPA), DCPA conversion over the Ni-VD catalyst was about two times higher than that over the Ni-IMP catalyst at 300 °C. It is probably due to the fact that the Ni-VD catalyst, which had low contents of nickel aluminate species compared to the Ni-IMP catalyst, exhibited higher degree of reduction than the Ni-IMP catalyst at pretreatment conditions. The difference in DCPA conversion between two catalysts was closely related to the degree of reduction of nickel species and the amounts of adsorption of DCPA onto the catalyst as well.

Comparison of risk factors and clinical responses to proton pump inhibitors in patients with erosive oesophagitis and non‐erosive reflux disease

Background  There has been no report on the response to proton pump inhibitor (PPI) therapy and on‐demand or the relapse rate of non‐erosive reflux disease (NERD) and erosive oesophagitis in Korea.

Integrated microfluidic array plate (iMAP) for cellular and molecular analysis

Just as the Petri dish has been invaluable to the evolution of biomedical science in the last 100 years, microfluidic cell assay platforms have the potential to change significantly the way modern biology and clinical science are performed. However, an evolutionary process of creating an efficient microfluidic array for many different bioassays is necessary. Specifically for a complete view of a cell response it is essential to incorporate cytotoxic, protein and gene analysis on a single system. Here we present a novel cellular and molecular analysis platform, which allows access to gene expression, protein immunoassay, and cytotoxicity information in parallel. It is realized by an integrated microfluidic array plate (iMAP). The iMAP enables sample processing of cells, perfusion based cell culture, effective perturbation of biologic molecules or drugs, and simultaneous, real-time optical analysis for different bioassays. The key features of the iMAP design are the interface of on-board gravity driven flow, the open access input fluid exchange and the highly efficient sedimentation based cell capture mechanism (∼100% capture rates). The operation of the device is straightforward (tube and pump free) and capable of handling dilute samples (5-cells per experiment), low reagent volumes (50 nL per reaction), and performing single cell protein and gene expression measurements. We believe that the unique low cell number and triple analysis capabilities of the iMAP platform can enable novel dynamic studies of scarce cells.

Numerical Simulation of the Effects of the Design Feature of a Cyclone and the Inlet Flow Velocity on the Separation of CO2 Particles from a CO2-COF2 Mixture

In synthesizing COF2 from CO, a considerable amount of CO2 is produced. A method of solidifying CO2 at low temperature and separating CO2 particles from the COF2 gas using a cyclone was designed and the separation efficiency according to the cyclone feature was studied. Optimal sizing and operation conditions of the cyclone were investigated by reviewing the flow velocity profile and the particle trajectory using a numerical analysis with computational fluid dynamics (CFD). The effects of the inlet flow velocity and the ratio of the cyclone diameter to the cone length (D/L) on the recovery efficiency were estimated. Results revealed that the separation efficiency increases with an increase in the ratio of D/L and a decrease in the cyclone size. The recovery efficiency of CO2 increases with the increase in the inlet flow velocity. Based on these results, we could propose a concept and methodology to design the optimal features and sizing of a cyclone suitable for separating solid CO2 from gaseous COF2 at low temperature.

Doping effect of viologen on photoconductive device made of poly (p-phenylenevinylene)

We report the photovoltaic properties of the donor‐acceptor composite system of poly ( p-phenylenevinylene !~ PPV! and viologen. We observed the significant enhancement of photocurrent with increasing the doping ratio of viologen. The maximum photocurrent of viologen-doped PPV was nine times as high as that of the pristine PPV. The maximum quantum yield and photosensitivity are 13% ~electron/photon! and 0.05 A/W, respectively, at low bias voltage ~2 2V !. The increase of photocurrent is explained with the efficient charge separation that resulted from the transfer of photoexcited electrons from PPV to viologen. The mixture of PPV and viologen can be used as a sensitive photodiode material.

Finely-dispersed Ni/Cu catalysts supported on mesoporous silica for the hydrodechlorination of chlorinated hydrocarbons

Abstract Ni/Cu and Ni catalysts supported on the mesoporous silica were prepared via grafting, metal adsorption and calcination steps. The prepared catalyst was characterized using XRD, TEM, N 2 sorption, and SAXS. Pore structure of the support was maintained throughout the preparation procedures. In addition, no specific metal particle image was appeared in XRD, because the metal particles are highly dispersed in the support as a very small size. Hydrodechlorination of TCEa (Trichloroethane) was selected as a model system to test the catalytic activity and selectivity to VCM. The activity of Ni/Cu-E-SBA is higher than that of Ni-E-SBA. The decrease in activity of Ni/Cu-E-SBA was much slow, because copper was added in the Ni catalyst. Cu may plays an important role to retard the deactivation by, such as coking. Further research is on progress. 97% selectivity to VCM was achieved after about 600min on Ni/Cu-E-SBA catalyst.

Preparation of NaCl-incorporated plugged mesoporous silica using a cost-effective precursor and applications to the hydrodechlorination of chlorinated hydrocarbons

The preparation of SBA-15 type plugged mesoporous silica using an inexpensive silica source in a two-step process is described. The resulting material was used as a catalyst support for a hydrodechlorination (HDC) reaction. The structure and morphology of the mesoporous silica and catalysts were determined using trasmission electron microscopy (TEM), small angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). The contents and particle size of the metal incorporated into the catalysts were measured by ICP atomic emission spectrometry (ICP-AES) and X-ray diffraction analysis (XRD). The material (hereafter referred to as 2MS) included about 2% Na in the form of NaCl. The pore structures of SBA-15 and 2MS were similar but 2MS showed an atypical plugged shape of the N2 desorption isotherm. Furthermore, the pore wall thickness was quite high (5 nm), and particles were large and in close proximity to each other in the 2MS. The micropore area ratio measured using a t-plot method was large, over 25%. When a 2MS-supported palladium catalyst was used for hydrodechlorination of 1,1,2-trichloroethane, the catalyst had a stronger resistance to deactivation.

Functionalized mesoporous adsorbents for Pt(II) and Pd(II) adsorption from dilute aqueous solution

Abstract The surface of the SBA-15 was functionalized with imidazole or thiol functional group via grafting method. Binding behaviors of the adsorbents toward Pt(II) and Pd(II) were examined. The properties of the adsorbents such as pore structure and pore uniformity were also investigated. The pore structure of as-synthesized adsorbents was conserved throughout the preparing steps. The results showed that imidazole- or thiol-functionalized adsorbents showed a high affinity for Pt(II) and Pd(II) metals in aqueous solution.