Kyung-Jo Kim

In vitro induction of differentiation by ginsenosides in F9 teratocarcinoma cells

The aim of this study was to determine the ability of the ginsenosides, extracts of Panax ginseng C.A. Meyer, to cause differentiation of F9 teratocarcinoma stem cells as a model system. F9 stem cells cultured in the presence of the ginsenosides together with dibutyryl cyclic AMP (dbcAMP) became parietal endoderm-like cells. Moreover, the expression of differentiation marker genes, such as laminin B1 and type IV collagen, was increased after treatment with the ginsenosides. Among the various purified ginsenosides, Rh1 and Rh2 were the most effective at causing differentiation of F9 cells. Since ginsenosides and glucocorticoid hormone have similar chemical structures, we examined the possibility of the involvement of a glucocorticoid receptor (GR) in the differentiation process induced by the ginsenosides. According to Southwestern blot analysis, a 94 kDa protein regarded as a GR was detected in F9 cells cultured in the medium containing the ginsenosides Rh1 or Rh2. In addition, F9 stem cells treated with the ginsenosides Rh1 or Rh2 and with RU486, a glucocorticoid antagonist with a high affinity for the GR, did not differentiate into endoderm cells morphologically, and the expression of laminin B1 gene was not induced in these cells. In a gel mobility shift assay, protein factors capable of binding to the glucocorticoid responsive element (GRE) specifically were detected in nuclear extracts of the ginsenoside-treated F9 cells. Moreover, overexpression of GR by cotransfection of GR expression vector and GRE-luciferase vector enhanced the transactivation activity of GRE promoter in the presence of ginsenosides Rh1 or Rh2 and was further augmented by dbcAMP. In addition, ginsenosides Rh1 and Rh2 bound to a GR assessed by whole-cell binding assay, even though the specific binding affinity was weaker compared to dexamethasone. Based on these data, we suggest that the ginsenosides Rh1 and Rh2 cause the differentiation of F9 cells and the effects of ginsenosides might be exerted via binding with a GR or its analogous nuclear receptor.

Strain induced tunable wavelength filters based on flexible polymer waveguide Bragg reflector

A tunable wavelength filter is demonstrated by imposing a strain on a polymeric Bragg reflection waveguide fabricated on a flexible substrate. The highly elastic property of flexible polymer device enables much wider tuning than the silica fiber. To produce a uniform grating pattern on a flexible plastic substrate, a post lift-off process along with an absorbing layer is incorporated. The flexible Bragg reflector shows narrow bandwidth, which is convincing the uniformity of the grating structure fabricated on plastic film. By stretching the flexible polymer device, the Bragg reflection wavelength is tuned continuously up to 45 nm for the maximum strain of 31,690 muepsilon, which is determined by the elastic expansion limit of waveguide polymer. From the linear wavelength shift proportional to the strain, the photoelastic coefficient of the ZPU polymer is found.

Flexible polymer waveguide tunable lasers

A flexible polymeric Bragg reflector is fabricated for the purpose of demonstrating widely tunable lasers with a compact simple structure. The external feedback of the Bragg reflected light into a superluminescent laser diode produces the lasing of a certain resonance wavelength. The highly elastic polymer device enables the direct tuning of the Bragg wavelength by controlling the imposed strain and provides a much wider tuning range than silica fiber Bragg gratings or thermo-optic tuned polymer devices. Both compressive and tensile strains are applied within the range from -36000 microepsilon to 35000 microepsilon, so as to accomplish the continuous tuning of the Bragg reflection wavelength over a range of up to 100 nm. The external feedback laser with the tunable Bragg reflector exhibits a repetitive wavelength tuning range of 80 nm with a side mode suppression ratio of 35 dB.

Optical Current Sensors Consisting of Polymeric Waveguide Components

Optical current sensors are demonstrated based on polarization rotated reflection interferometry by incorporating polymeric optical waveguide components. Polarization maintaining 3-dB couplers, TE-pass waveguide polarizers, and thermo-optic phase modulators are designed and fabricated in this work in order to provide essential building blocks for constructing the current sensors. The phase difference between the two circularly polarized waves imposed by the Faraday effect of the optical fiber is detected using the interferometric optical sensor consisting of the polymeric components. To remove the bending induced birefringence, the optical fiber wound around a ceramic frame is annealed at 850°C for 24 hours. The reflection interferometer comprising the polymer waveguide components operates with good linearity proportional to the monitoring current.

Polymer Waveguide Label-Free Biosensors With Enhanced Sensitivity by Incorporating Low-Refractive-Index Polymers

Label-free biosensors consisting of polymeric waveguides with a Bragg reflection grating are demonstrated for the purpose of highly sensitive protein detectors. Due to the unique nanoimprinting and injection molding processes, polymer waveguide devices have the potential to provide cost-effective disposable biosensors as long as a robust compatible immunoassay process is developed. A fluorinated polymer material with the lowest refractive index, which is close to that of the saline solution, is used for the sensor waveguide, in order to increase the effective index modulation efficiency. The large contrast waveguide exhibits a 1.9 times higher sensitivity for the detection of the variation of the cover index compared to low-contrast sensors. Bragg reflectors with a 3-dB bandwidth of 0.9 nm are fabricated using laser interferometry and dry etching of the core layer by 50 nm. An immunoassay experiment to detect the concentration of antibiotin is performed by measuring the peak wavelength shift of the Bragg reflection sensors. By using a blocking buffer, it is possible to obtain a stable saturated output signal by preventing the nonspecific binding. In the experiment to measure the antibiotin concentration, the sensor exhibits linear correspondence of peak wavelength shift for the concentrations.

Near-infrared tunable lasers with polymer waveguide Bragg gratings.

Wavelength tunable lasers operating at near infrared (NIR) wavelength are demonstrated through the thermo-optic (TO) refractive index tuning of polymer waveguide Bragg reflectors. The polymer-waveguide device has superior TO efficiency for substantially changing the refractive index, and it enables direct tuning of the Bragg reflection wavelength over a wide range. The waveguide is optimized for NIR wavelengths, and a third-order Bragg reflector is incorporated for facilitating fabrication of the grating. The laser exhibits an output power of 0 dBm, a side-mode suppression ratio of 40 dB, and a tuning range of 21 nm.

Optical Pressure Sensors Based on Vertical Directional Coupling With Flexible Polymer Waveguides

An optical pressure sensor based on the radiation coupling in vertical direction between a channel waveguide and a flexible polymer waveguide is proposed. The flexible waveguide is bent by an applied pressure to reduce the separation distance between the two waveguides so that the light propagating in the channel waveguide is radiated into the flexible planar waveguide. By applying a pressure ranging from 100 to 500 kPa, the output intensity modulation of 20 dB is obtained by virtue of the efficient phase matched coupling between the waveguides made of the same polymer material. The large extinction ratio is useful to measure the pressure precisely for a wide range.

Polymer waveguide integrated-optic current transducers

Various functional optical devices are integrated on a single chip in order to construct optical current transducers based on polarization rotated reflection interferometry, which consists of polarization maintaining 3-dB couplers, TE-pass polarizers, TE/TM polarization converters, and thermo-optic phase modulators. By virtue of the device integration, the sensor exhibited good linearity, and excellent accuracy with an error less than 0.2%. The integrated-optic device provides inherent polarization maintaining characteristics and precise controllability of the optical path length in the interferometric sensor. Single chip integration reduces the complexity of the interferometry, and enables mass-production of low-cost high performance current sensors.

Polymeric waveguide biosensors with calixarene monolayer for detecting potassium ion concentration

Biophotonic sensors based on a polymer waveguide with Bragg reflection gratings are proposed in this work. For developing low-cost disposable sensors, UV curable polymer materials are utilized to demonstrate the waveguide sensors. The grating pattern is formed on the core layer of a polymer waveguide by exposing a laser interference pattern on a photoresist. To detect a small amount of analyte molecule through a specific binding, a calixarene crown molecule is immobilized on a sensing interface. Bragg reflection peak movement is observed depending on the potassium ion concentration dissolved in phosphate buffered saline solution. It has been confirmed experimentally that the sensor could detect the potassium ion concentration on the order of 1pM.

Polarization-Splitting Waveguide Devices Incorporating Perfluorinated Birefringent Polymers

Low-loss perfluorinated polymers with a controllable optical birefringence were synthesized for the purpose of fabricating polarization-splitting waveguide devices, which have become an essential part of polarization-multiplexed coherent optical communications. The birefringent polymer was embedded on one branch of the asymmetric Y-branch waveguide to produce polarization-dependent mode evolution due to the effective birefringence. The device with a branch angle of 1/300 rad and birefringence of 0.007 showed a crosstalk of -25 dB and an insertion loss of 1.5 dB from fiber to fiber. The polarization splitters based on adiabatic mode evolution exhibited negligible wavelength dependence and large tolerance in waveguide dimension.