Sang-Don Jung

Centrifugal enhancement of Kaposi's sarcoma-associated virus infection of human endothelial cells in vitro

In order to improve the efficiency of infection of primary human endothelial cells in vitro of Kaposis sarcoma-associated herpesvirus (KSHV), the effect of low speed centrifugation was investigated. The recombinant KSHV, BAC36, was used to examine the centrifugal enhancement of KSHV. Infectivity was estimated by green fluorescent protein (GFP) expression and real-time RT-PCR. The enhancement of infectivity was dependent upon the time and force of centrifugation in human umbilical vein endothelial cells (HUVECs). Centrifugation enhanced the infectivity of KSHV by up to 70 fold compared to non-centrifugal control infection for the same period of time; viral mRNA expression was also enhanced by centrifugation. HUVECs that were centrifuged before infection with KSHV displayed no enhancement in infectivity; therefore, enhancement is believed to occur during centrifugation. In addition, the mechanisms of infection including the initial viral attachment to cells, lipid rafts, and clathrin-mediated and caveolae endocytosis appear to be similar in KSHV infection with and without centrifugal enhancement. These results show that low speed centrifugation could be a useful tool for improving the efficiency of KSHV infection in vitro.

Enhancement of neuronal cell adhesion by covalent binding of poly-d-lysine

We have prepared the poly-d-lysine (PDL) bound surfaces for neuron cell culture by covalent binding between the poly-d-Lysine and substrates and investigated neuronal cell adhesion properties and cell growth morphology. The number of neuronal cell and the number of neurite per neuronal cell on PDL bound surfaces was much more than those on PDL coated surfaces and also the neuronal cells on PDL bounded surfaces survived a longer time. On the pattern of covalently bound PDL, neuronal cells and their neurites are confined within the grid line leading to patterned neuronal networks with the long-term survival.

In vitro extracellular recording and stimulation performance of nanoporous gold-modified multi-electrode arrays.

OBJECTIVE Nanoporous gold (Au) structures can reduce the impedance and enhance the charge injection capability of multi-electrode arrays (MEAs) used for interfacing neuronal networks. Even though there are various nanoporous Au preparation techniques, fabrication of MEA based on low-cost electro-codeposition of Ag:Au has not been performed. In this work, we have modified a Au MEA via the electro-codeposition of Ag:Au alloy, followed by the chemical etching of Ag, and report on the in vitro extracellular recording and stimulation performance of the nanoporous Au-modified MEA. APPROACH Ag:Au alloy was electro-codeposited on a bilayer lift-off resist sputter-deposition passivated Au MEA followed by chemical etching of Ag to form a porous Au structure. MAIN RESULTS The porous Au structure was analyzed by scanning electron microscopy and tunneling electron microscopy and found to have an interconnected nanoporous Au structure. The impedance value of the nanoporous Au-modified MEA is 15.4 ± 0.55 kΩ at 1 kHz, accompanied by the base noise V rms of 2.4 ± 0.3 μV. The charge injection limit of the nanoporous Au-modified electrode estimated from voltage transient measurement is approximately 1 mC cm(-2), which is comparable to roughened platinum and carbon nanotube electrodes. The charge injection capability of the nanoporous Au-modified MEA was confirmed by observing stimulus-induced spikes at above 0.2 V. The nanoporous Au-modified MEA showed mechanical durability upon ultrasonic treatment for up to an hour. SIGNIFICANCE Electro-codeposition of Ag:Au alloy combined with chemical etching Ag is a low-cost process for fabricating nanoporous Au-modified MEA suitable for establishing the stimulus-response relationship of cultured neuronal networks.

The enhancement of electroluminescence efficiency by molecular doping

Abstract We report on the investigation of electroluminescence (EL) for a dye-doped polymer. This doping system consists of main chain conjugated poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and highly fluorescent dye rubrene. We fabricated many EL samples of various doping ratios due to the good solubility of rubrene and MEH-PPV in organic solvents. Low operation voltage and high EL efficiency were obtained simultaneously in the molecularly doped system. We made EL cells having an emission efficiency 10 times higher than that of an undoped MEH-PPV diode with nearly the same turn-on voltage.

Fabrication of multi-electrode array platforms for neuronal interfacing with bi-layer lift-off resist sputter deposition

We report a bi-layer lift-off resist (LOR) technique in combination with sputter deposition of silicon dioxide (SiO2) as a new passivation method in the fabrication of a multi-electrode array (MEA). Using the photo-insensitive LOR as a sacrificial bottom layer and the negative photoresist as a patterning top layer, and performing low-temperature sputter deposition of SiO2?followed by lift-off, we could successfully fabricate damage-free indium-tin oxide (ITO) and Au MEA. The bi-layer LOR sputter deposition processed Au MEA showed an impedance value of 6???105?? (at 1?kHz), with good consistency over 60 electrodes. The passivation performance of the bi-layer LOR sputter-deposited SiO2?was tested by electrodepositing Au nanoparticles (NPs) on the Au electrode, resulting in the well-confined and uniformly coated Au NPs. The bi-layer LOR sputter deposition processed ITO, Au, and Au NP-modified MEAs were evaluated and found to have a neuronal spike recording capability at a single unit level, confirming the validity of the bi-layer LOR sputter deposition as an effective passivation technique in fabrication of a MEA. These results suggest that the damage-free Au MEA fabricated with bi-layer LOR sputter deposition would be a viable platform for screening surface modification techniques that are available in neuronal interfacing.

Structural study of a poly(methylmethacrylate) Langmuir–Blodgett film on a graphite surface by scanning tunneling microscope

In this study, molecular configurations of three different stereoregular poly(methylmethacrylate) (PMMA) (isotactic, atactic, and syndiotactic PMMA) monolayers, which were transferred onto graphite substrates by the Langmuir–Blodgett (LB) technique, were investigated using scanning tunneling microscope (STM). STM images of monolayer films taken in air in the constant height mode showed various types of film structures. First, polymer films in their different forms always showed long‐range ordered chain structures. Second, these polymer chains were generally observed to arrange themselves in parallel chains with no backbone crossovers. However, the packing density of polymer chains on the surface varied with change of scanning area presumably due to the nonuniformity of the LB film and the effect of thermal fluctuation of polymer chains on the film. Third, a monolayer film of isotactic PMMA film showed the coexistence of helical and linear chains in most of the film areas suggesting that the structural tra...

Electroluminescent Properties of Novel Silyl-Disubstituted Soluble PPV Derivative

Abstract Light-emitting properties of a solvent processable poly(1,4-phenylenevinylene) (PPV) derivative, poly[2-bis(dimethyloctylsilyl)-1,4-phenylenevinylene] (BDMOS-PPV) have been studied Synthesized BDMOS-PPV is highly fluorescent and the measured absolute PL quantum efficiency is exceeding 60%. Single layer electroluminescent device (ITO/BDMOS-PPV/Al) exhibits an emission maximum at 515 nm which corresponds to the green region.

Degradation process in polymeric electroluminescent devices

Abstract To investigate the initial degradation process in polymeric electroluminescent (EL) devices, in situ measurement of photoluminescence image change was carried out. The Al electrode was sunk or protruded during the device operation. Formation of the dented dark spot is observed by using an atomic force microscope and a scanning electron microscope, which is the critical factor of the degradation.

Electrode effects on the low-frequency dielectric properties of (Ba, Sr)TiO3 thin films prepared by pulsed laser ablation

Abstract (Ba, Sr)TiO3(BST) thin films were prepared by pulsed laser deposition on the perovskite conductive oxide LaNiO3 (LNO), YBa2Cu3O7−δ(YBCO) films, and Pt as a bottom electrode. The crystalline structures and surface microstructrue of the BST deposited on several substrates were characterized by x-ray diffraction measurement and scanning electron microscopy, respectively. The electrode effects on low-frequency dielectric behavior of BST thin films were investigated. The complex dielectric constants of the films were measured as a function of frequency in the frequency range from 0.1 Hz to 10 MHz. BST films grown on metallic oxide substrates exhibited marked dielectric relaxation below 10 MHz. This low frequency dielectric relaxations is attributed to the ionized space charge carriers such as the oxygen vacancies and cation defects in BST film, and the interfacial polarization in the grain boundary region and the electrode/film interface.

Effects of photobleaching wavelength on the resulting refractive index profiles in nonlinear optical polymeric thin films

Photobleaching process and the resulting refractive index profiles of the nonlinear optical polymeric thin films have been investigated for the formation of active and passive waveguide devices. The material, a PMMA based copolymer with stilbene derivative as side chain, is formed to thin films by spin coating. Two different wavelengths of 458nm and 514.5nm generated from Ar + ion laser are selected as the bleaching light, which are located near the absorption maximum and the absorption edge of the material, respectively. Bleaching rate of the thin films measured by transmission experiment is found to be linearly proportional to the power of the incident light, indicating that the photobleaching is one photon process. Evolution of the refractive index profiles with bleaching time is obtained using the inverse WKB method with the measured guiding mode indices. The refractive index profiles bleached with 458nm are steeper than those bleached with 514.5nm as expected. A simple kinetic model with the parameters deduced from the transmission experiment is used to delineate the refractive index profiles and the resulting profiles are compared with the experimental ones.