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Donghyun Kim

Publications and source records attributed to Donghyun Kim.

18 recordsLinked to original sources
PubMed2007

Sensitivity analysis of a nanowire-based surface plasmon resonance biosensor in the presence of surface roughness.

We have investigated the effect of surface roughness on the sensitivity of conventional and nanowire-based surface plasmon resonance (SPR) biosensors. The theoretical research was conducted using rigorous coupled-wave analysis with Gaussian surface profiles of gold films determined by atomic force microscopy. The results suggest that, when surface roughness ranges near 1 nm, the sensitivity of a conventional SPR system is not significantly affected regardless of the correlation length. For a nanowire-based SPR biosensor, however, we have found that the sensitivity degrades substantially with decreasing correlation length. In particular, at a correlation length smaller than 100 nm, a random rough surface may induce destructive coupling between excited localized surface plasmons, which can lead to prominent reduction of sensitivity enhancement.

Journal Article↗
PubMed2006

Cytochemical alterations in the rat retina by LPS administration.

LPS-induced inflammation and changes in protein phosphorylation and the JAK-STAT pathway accompanying glial activation after LPS treatment, were followed by analyzing secreted proinflammatory cytokine levels. The administration of LPS caused tyrosine phosphorylation of STAT3 in retinae and induced glial fibrillary acidic protein. (GFAP) from the nerve fiber layer to the ganglion cell layer. Our results suggest that the LPS-induced activation of the JAK2/STAT3 signaling pathway may play a key role in the induction of astrogliosis. However, no significant increase in vimentin, OX-42 or inducible nitric oxide synthase (iNOS) expressions were observed after LPS administration. Sphingosine kinase catalyzes the conversion of sphingosine to sphingosine-1-phosphate (So-1-P), a sphingolipid metabolite that plays important roles in angiogenesis, inflammation, and cell growth. In the present study, it was found that sphingolipid metabolite levels were elevated in the serum and retinae of LPS-injected rats. To further investigate the chronic effect of increased So-1-P in the retina, So-1-P was infused intracerebroventricularly (i.c.v.) into rats using an osmotic minipump at 100 pmol/10 microl h(-1) for 7 days, and was found to increase retinal GFAP expression. These observations suggest that LPS induces the activation of retinal astrocytes via JAK2/STAT3 and that LPS affects So-1-P generation. Our findings also suggest that elevated So-1-P in the retina and/or in serum could induce cytochemical alterations in LPS treated or inflamed retinae.

Animals↗
PubMed2006

Antibody-based surface plasmon resonance detection of intact viral pathogen.

Surface plasmon resonance (SPR) technique was used to directly detect an intact form of insect pathogen: the baculovirus, Autographa californica multiple nuclear polyhedrosis virus (AcMNPV). An SPR sensor chip with three bio-functional layers was used to detect the intact AcMNPV: amine-reactive crosslinker with a disulfide bond that chemisorbs to gold film, Protein A, and a mouse IgG monoclonal antibody raised against a surface protein of the target viral pathogen. A two-channel (reference & test) micro-fluidic SPR system is used for reliable measurement. Bio-specific response to the AcMNPV is compared with the response for tobacco mosaic virus (TMV) as control. Successive exposure of the sensor chip to both viruses verifies a specific response to AcMNPV. This serves as a prerequisite to the development of a new type of viral pathogen detection sensors.

Antibodies, Viral↗
PubMed2006

Profile effect on the feasibility of extinction-based localized surface plasmon resonance biosensors with metallic nanowires.

We investigate the effect of the cross-sectional profile of an array of metallic nanowires on the feasibility of a localized surface plasmon resonance (LSPR) biosensor. Calculations were performed using rigorous coupled-wave analysis with an emphasis on the extinction properties of the LSPR structure. The results indicate that the nanowire structure, particularly that of a T-profile, delivers an extremely linear sensing performance over a wide range of the target refractive index with much enhanced sensitivity. The extinction-based LSPR structure also involves a relatively large dimension and thus is expected to provide a feasible biosensor using current semiconductor technology.

Biosensing Techniques↗
PubMed2006

Flavonoids as mushroom tyrosinase inhibitors: a fluorescence quenching study.

Flavonoids, a group of naturally occurring antioxidants and metal chelators, can be used as tyrosinase inhibitors due to their formation of copper-flavonoid complexes. Thus, to investigate the underlying inhibition mechanism, a large group of flavonoids from several major flavones and flavonols were tested using fluorescence quenching spectroscopy. In addition, large differences in the tyrosinase inhibitory activities and chelating capacities according to the location of the hydroxyl group(s) in combination with the A and B rings in the flavonoids were confirmed. Accordingly, the major conclusions from this work are as follows: (i) The tyrosinase inhibitory activity is not only dependent on the number of hydroxyl groups in the flavonoids, (ii) the enzyme is primarily quenched by the hydroxyl group(s) of A and B rings on the ether side of the flavonoids, and (iii) the tyrosinase inhibitory activity of 7,8,3',4'-tetrahydroxyflavone is supported by a virtual model of docking with the mushroom tyrosinase, which depicts the quenching of the enzyme. The results also demonstrated that the dihydroxy substitutions in the A and B rings are crucial for Cu2+-chelate formation, thereby influencing the tyrosinase inhibitory activity.

Agaricales↗
PubMed2006

Attenuation of morphine tolerance and withdrawal syndrome by coadministration of nalbuphine.

Morphine has been used widely on the treatment of many types of chronic pain. However the development of tolerance to and dependence on morphine by repeat application is a major problem in pain therapy. The purpose of the present study was to investigate whether combined administration of nalbuphine with morphine affects the development of tolerance to and dependence on morphine. We hypothesize that the use of nalbuphine, kappa-agonist may prove to be useful adjunct therapy to prevent morphine-induced undesirable effects in the management of some forms of chronic pain. Morphine (10 mg/kg) was injected to rats intraperitoneally for 5 day. The variable dose of nalbuphine (0.1, 1.0 and 5.0 mg/kg) was administered (i.p.) in combination with morphine injection. The development of morphine tolerance was assessed by measuring the antinociceptive effect with the Randall-Selitto apparatus. The development of dependence on morphine was determined by the scoring the precipitated withdrawal signs for 30 min after injection of naloxone (10 mg/kg, i.p.). Nalbuphine did not attenuate antinociceptive effect of morphine in rats. Interestingly, combined administration of morphine with nalbuphine (10:1) significantly attenuated the development of dependence on morphine. The elevation of [3H]MK-801 binding in frontal cortex, dentate gyrus, and cerebellum after chronic morphine infusion was suppressed by the coadministration of nalbuphine. In addition, the elevation of NR1 expression by morphine was decreased by the coadministration of nalbuphine in rat cortex. These results suggest that the coadministration of nalbuphine with morphine in chronic pain treatment can be one of therapies to reduce the development of tolerance to and dependence on morphine.

Analgesics, Opioid↗
PubMed2006

Synthesis and evaluation of biological properties of benzylideneacetophenone derivatives.

A series of yakuchinone B 1f and its analogs 1a-e was synthesized and evaluated for free radical scavenging, suppression of LPS-induced NO generation, cytotoxicity and anti-excitotoxicity in vitro. Compound 1c exhibited potent anti-excitotoxicity, while all compounds 1a-f showed considerable effects of free radical scavenging, suppression of LPS-induced NO generation, and cytotoxicity in microglia.

Animals↗
PubMed2006

Fitting-based determination of an effective medium of a metallic periodic structure and application to photonic crystals.

Effective permittivities of a metallic periodic structure for which the second-order effective-medium theory does not yield correct results were obtained by numerically fitting to rigorous-coupled-wave analysis (RCWA). The calculated effective medium showed good agreement with RCWA and minimal deviation in the long-wavelength limit with variation in angle of incidence, grating depth, superstrate, and fill factor. In terms of the standard deviation, the effective medium was least affected by the change in grating depths. The calculated effective permittivities were applied to a three-dimensional metallic photonic-crystal structure and produced a photonic bandgap that is consistent with published experimental data.

Journal Article↗
PubMed2006

Effect of resonant localized plasmon coupling on the sensitivity enhancement of nanowire-based surface plasmon resonance biosensors.

A nanowire-based surface plasmon resonance (SPR) is investigated as a structure that offers improved sensor performance. The results calculated by rigorous coupled-wave analysis on a model using a hexanedithiol self-assembled monolayer (SAM) indicate that the resonant coupling between localized surface plasmons (LSPs) of nanowires affects the sensitivity enhancement substantially, while the LSP resonance in a single nanowire also contributes. SPR characteristics change significantly by applying a SAM, which can give rise to zero sensitivity for a given SAM. The results suggest that a properly designed nanowire-based SPR biosensor can enhance sensitivity by an order of magnitude with reasonable detection properties.

Artifacts↗
PubMed2005

Performance uniformity analysis of a wire-grid polarizer in imaging polarimetry.

The polarimetric performance nonuniformity of a wire-grid polarizer (WGP) used in imaging polarimetry is investigated with a simple numerical model. The simulation results based on rigorous coupled-wave analysis show that the aperture ratio between the entrance pupil and the WGP significantly affects the uniformity among pixels of a WGP. Even with a WGP smaller than an imaging aperture, the results suggest that the design avoids incurring a Rayleigh anomaly, which causes a substantial increase in polarimetric nonuniformity. Minimizing the variation due to the characteristics of a WGP is important to reduce the likelihood of an error in imaging polarimetry.

Journal Article↗
PubMed2005

Portable in situ fluorescence cytometry of microscale cell-based assays.

A portable fluorescence cytometric system has been developed for characterizing chemical concentration and cellular status in microscale cell culture analog (microCCA) devices. Based on discrete optical components, the system provides a modular platform for real-time image measurements applicable to a variety of cell-based microassays. As a feasibility study, we investigated the real-time dynamics of daunorubicin uptake with cultured mouse L-cells in a microCCA compartment. Time course results measured by the portable fluorescence cytometric system confirmed that in the microCCA devices daunorubicin accumulation is proportional to the liquid turnover rate.

Animals↗
PubMed2005

Effect of the azimuthal orientation on the performance of grating-coupled surface-plasmon resonance biosensors.

The effect of azimuthal orientation on the electromagnetic coupling of surface plasmons with the incident and diffracted light of a grating-coupled surface-plasmon resonance (GC-SPR) biosensor is investigated, and its practical implications are explored. For this purpose a GC-SPR biosensor model is considered, and well-established rigorous coupled-wave analysis is used. Numerical results indicate significant variations in surface-plasmon resonance characteristics in connection with the interaction between surface-plasmon polaritons associated with multiple-order diffraction. The results are discussed as they relate to applications that require minimal rotation sensitivity.

Algorithms↗
PubMed2005

Polarization characteristics of a wire-grid polarizer in a rotating platform.

I explore the polarization characteristics of a wire-grid polarizer operating in a rotating platform using well-established rigorous coupled-wave analysis. The results show that the performance of a wire-grid polarizer evaluated in transmittance and extinction ratio is substantially degraded with rotation, although it is still more robust than that of a perfect polarizer. The performance may further deteriorate with inclined incidence due to an increased negative effect of a Rayleigh anomaly. Either a finer or a deeper grating reduces the adverse effect of rotation. Although implementation of such a grating is difficult, the rotation characteristics can be enhanced by means of pixelating the wire grids of various orientations and capturing the input images with a sufficiently high sampling rate.

Journal Article↗
PubMed2004

Reduction of coherent artifacts in dynamic holographic three-dimensional displays by diffraction-specific pseudorandom diffusion.

An electroholographic display based on diffraction-specific computation can reduce speckle by electronic diffusion through selective addition of a pseudorandom sequence. Intensity fluctuation as a result of the introduction of pseudorandom noise does not affect three-dimensional (3-D) images significantly since spatial windows formed by diffused basis fringes do not widen noticeably at low pseudorandom spread, whereas the features of the fluctuation are much smaller than human visual resolution. Experimental results obtained on the Massachusetts Institute of Technology holographic video system confirmed that the diffusion smooths 3-D images and improves the intensity nonuniformity among horizontal holographic lines.

Journal Article↗
PubMed2003

Design of a grating-based thin-film filter for broadband spectropolarimetry.

We propose a simple procedure for designing an integrated single-chip grating-based thin-film filter. A simulation from a rigorous coupled-wave analysis shows that structural adjustment based on the effective medium theory can achieve the desired integration without notable performance degradation. Our spectropolarimetric filter design maintains spectral filter characteristics, while its extinction ratio is significantly enhanced over the passband. The integrated spectropolarimetric filter can be a basis for building multispectral multipolarimetric filters for spectropolarimetry in remote-sensing applications.

Journal Article↗
PubMed2003

Imaging multispectral polarimetric sensor: single-pixel design, fabrication, and characterization.

A discrete-component approach was taken to establish the operational feasibility of a novel, imaging, midinfrared, multispectral, polarimetric sensor for remote-sensing application. The sensor is designed to exploit the spectral and polarimetric characteristics of the scene as discriminants. Pixelated multispectral filters and polarization filters were designed and fabricated on sapphire and Si substrates, respectively, and both were characterized. A single-pixel spectropolarimetric composite filter was characterized by use of a Fourier transform infrared spectrometer and a Pt-Si thermal-imaging camera. The experimental results show excellent agreement with theoretical predictions.

Journal Article↗
PubMed2002

PCDDs, PCDFs, and PCBs concentrations in breast milk from two areas in Korea: body burden of mothers and implications for feeding infants.

We determined breast milk concentration of polychlorinated dibenzo-p-dioxins (PCDDs)/polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) in 24 mothers living in Korea, and assessed the maternal body burden based on PCDDs/PCDFs and PCBs concentrations in breast milk and an infant intake rate through breast-feeding based on their concentration in breast milk. PCDDs/PCDFs and PCBs levels in breast milk from primipara mothers were found to be higher than those from multipara mothers. For total PCDDs/PCDFs TEQ level, 2,3,4,7,8-PeCDD was the predominant congener, and the proportion of 2,3,7,8-TCDD was less than 3% of total PCDDs/PCDFs TEQ level. For PCBs TEQ level, PCB-126 was the predominant congener. Maternal body burden levels of PCDDs/PCDFs and PCBs based on their concentrations in breast milk were 268-622 TEQ ng. The daily dioxin intakes of mothers were predicted to be 0.78-2.18 TEQ pg/kg/day for PCDDs/PCDFs and 0.34-0.66 TEQ pg/kg/ day for PCBs. For the first year, the body burden of an infant was predicted to be 212 TEQ ng and the daily intake of an infant was predicted to be 85 TEQ pg/kg/day, assuming the mean dioxin-related compounds concentration (27.54 TEQ pg/g fat).

Adult↗