Browsing by Author "Liang, Keng S."

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30 nm resolution x-ray imaging at 8 keV using third order diffraction of a zone plate lens objective in a transmission microscope
(2006-11-27)
Yin, Gung-Chian
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Song, Yen-Fang
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Tang, Mau-Tsu
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Chen, Fu-Rong
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Liang, Keng S.
A hard x-ray transmission microscope with 30 nm spatial resolution has been developed employing the third diffraction order of a zone plate objective. The microscope utilizes a capillary type condenser with suitable surface figure to generate a hollow cone illumination which is matched in illumination range to the numerical aperture of the third order diffraction of a zone plate with an outmost zone width of 50 nm. Using a test sample of a 150 nm thick gold spoke pattern with finest half-pitch of 30 nm, the authors obtained x-ray images with 30 nm resolution at 8 keV x-ray energy. (c) 2006 American Institute of Physics.
Dependence of the final-state effect on the coupling between a CdSe nanoparticle and its neighbors studied with photoemission spectroscopy
(2007-03-01)
Wu, Pin-Jiun
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Tsuei, Ku-Ding
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Hsieh, Meng-Ting
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Wei, Kung-Hwa
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Liang, Keng S.
A simple model based on an electrostatic calculation of the photoemission effect in the final state is used to characterize the energy shift, relative to bulk material, which is dependent on size in the photoemission spectra of organically passivated CdSe nanoparticles (NPs). For trioctylphosphine oxide/hexadecylamine-passivated NPs, the core-level shifts are well described with a model involving a static effect in the final state. After the NPs are treated with pyridine, the energy shifts are smaller; this decrease is ascribed to a dynamic effect in the final state describing a finite lifetime, on a femtosecond scale, of the photohole residing in the NP. This condition is intimately related to the coupling between the NP and metallic substrate and among NPs themselves. For the valence-band edge, an additional effect of the initial state due to quantum confinement is required to elucidate the energy shift. We find that this initial-state shift is smaller than a prediction according to a semiempirical pseudopotential calculation.
Electronic structure of pyrochlore Cd(2)Re(2)O(7)
(2009-05-13)
Huang, Shih-Wen
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Jeng, Horng-Tay
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Lin, J-Y
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Chang, W. J.
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Chen, J. M.
Detailed band structure calculations have been performed for Cd(2)Re(2)O(7) in high-, middle- and low-temperature (T) phases. The calculations are based on the observed lattice structures from x-ray diffraction measurements. The spin-orbit interaction is incorporated self-consistently in both the generalized gradient approximation (GGA) and the GGA plus Hubbard U (GGA + U) approaches. It is found that the on-site U has negligible effects on the Re 5d band structures; therefore both the GGA and GGA + U Re 5d band energies agree well with the observed O K-edge x-ray absorption spectroscopy (XAS) spectrum, whereas the Cd 4d band energy observed from photoemission spectroscopy can only be correctly reproduced by GGA + U calculations, indicating the relatively itinerant Re 5d and localized Cd 4d electrons. On the other hand, the spin-orbit coupling gives rise to nontrivial spin and orbital magnetic moments for the middle-T phase. Most unexpectedly, we found that the low-T phase exhibits quasi-two-dimensional Fermi surfaces. The calculated carrier numbers for the three phases are, at least qualitatively, consistent with the measured Hall coefficient.
Electronic structure of pyrochlore Cd2Re2O7
(2009-05-13)
Huang, Shih-Wen
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Jeng, Horng-Tay
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Lin, J-Y
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Chang, W. J.
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Chen, J. M.
Detailed band structure calculations have been performed for Cd2Re2O7 in high-, middle- and low-temperature (T) phases. The calculations are based on the observed lattice structures from x-ray diffraction measurements. The spin-orbit interaction is incorporated self-consistently in both the generalized gradient approximation (GGA) and the GGA plus Hubbard U (GGA + U) approaches. It is found that the on-site U has negligible effects on the Re 5d band structures; therefore both the GGA and GGA + U Re 5d band energies agree well with the observed O K-edge x-ray absorption spectroscopy (XAS) spectrum, whereas the Cd 4d band energy observed from photoemission spectroscopy can only be correctly reproduced by GGA + U calculations, indicating the relatively itinerant Re 5d and localized Cd 4d electrons. On the other hand, the spin-orbit coupling gives rise to nontrivial spin and orbital magnetic moments for the middle-T phase. Most unexpectedly, we found that the low-T phase exhibits quasi-two-dimensional Fermi surfaces. The calculated carrier numbers for the three phases are, at least qualitatively, consistent with the measured Hall coefficient.
Endosomal escape and transfection efficiency of PEGylated cationic liposome-DNA complexes prepared with an acid-labile PEG-lipid
(2012-06-01)
Chan, Chia-Ling
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Majzoub, Ramsey N.
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Shirazi, Rahau S.
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Ewert, Kai K.
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Chen, Yen-Ju
Cationic liposome-DNA (CL-DNA) complexes are being pursued as nonviral gene delivery systems for use in applications that include clinic trials. However, to compete with viral vectors for systemic delivery in vivo, their efficiencies and pharmacokinetics need to be improved. The addition of poly (ethylene glycol)-lipids (PEGylation) prolongs circulation lifetimes of liposomes, but inhibits cellular uptake and endosomal escape of CL-DNA complexes. We show that this limits their transfection efficiency (TE) in a manner dependent on the amount of PEG-lipid, the lipid/DNA charge ratio, and the lipid membrane charge density. To improve endosomal escape of PEGylated CL-DNA complexes, we prepared an acid-labile PEG-lipid (HPEG2K-lipid, PEG MW 2000) which is designed to lose its PEG chains at the pH of late endosomes. The HPEG2K-lipid and a similar but acid-stable PEG-lipid were used to prepare PEGylated CL-DNA complexes. TLC and dynamic light scattering showed that HPEG2K-CL-DNA complexes are stable at pH 7.4 for more than 24 h, but the PEG chains are cleaved at pH 5 within 1 h, leading to complex aggregation. The acid-labile HPEG2K-CL-DNA complexes showed enhanced TE over complexes stabilized with the acid-stable PEG-lipid. Live-cell imaging showed that both types of complexes were internalized to quantitatively similar particle distributions within the first 2 h of incubation with cells. Thus, we attribute the increased TE of the HPEG2K-CL-DNA complexes to efficient endosomal escape, enabled by the acid-labile HPEG2K-lipid which sheds its PEG chains in the low pH environment of late endosomes, effectively switching on the electrostatic interactions that promote fusion of the membranes of complex and endosome. (c) 2012 Elsevier Ltd. All rights reserved.
Energy shift of photoemission spectra for organics-passivated CdSe nanoparticles: The final-state effect
(2007-01-01)
Wu, Pin-Jiun
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Tsuei, Ku-Ding
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Wei, Kung-Hwa
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Liang, Keng S.
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材料科學與工程學系
Size-dependent energy shift of photoemission spectra with respect to bulk sample has been examined for colloidally prepared CdSe nanoparticles with a series of particle sizes. The core-level shifts are well described by a theoretical calculation based on a final-state effect model, whereas an additional initial-state effect due to quantum confinement is required to elucidate the valence-band edge shifts. The results indicate that the interaction between the photohole and the dielectric background in the final state has to be considered in photoemission measurements for organics-passivated nanoparticles. The calculated results in the literature appear to overestimate the initial-state effect compared to our experimental observation. (c) 2006 Elsevier Ltd. All rights reserved.
Envelope Structure of Human eNOS Protein Revealed by Small-Angle X-ray Scattering
(2012-04-01)
Chen, Chun-Yu
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Chen, Pei-Feng
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Hwu, Yeukuang
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Jeng, U-Ser
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Wu, Kun-Yu
We investigate the solution structure of human eNOS protein by using synchrotron small-angle X-ray scattering (SAXS). The pair-correlation analysis of the profile shows the radius of gyration (R-g) and maxima dimension (D-max) of 6.87 +/- 0.03 nm and 22 nm, respectively. The ratio of D-max and R-g revealed that the protein was an extended conformation. The ab initio shape determination and rigid-body calculations were performed to reconstruct the real-space structure of eNOS in solution. The result shows that human eNOS form homodimer form in solution with the closed contact of two oxygenase domains.
Fluorescence microscopy colocalization of lipid-nucleic acid nanoparticles with wildtype and mutant Rab5-GFP: A platform for investigating early endosomal events
(2015-06-01)
Majzoub, Ramsey N.
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Chan, Chia-Ling
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Ewert, Kai K.
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Silva, Bruno F. B.
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Liang, Keng S.
Endosomal entrapment is known to be a major bottleneck to successful cytoplasmic delivery of nucleic acids (NAs) using cationic liposome-NA nanopartides (NPs). Quantitative measurements of distributions of NPs within early endosomes (EEs) have proven difficult due to the sub-resolution size and short lifetime of wildtype EEs. In this study we used Rab5-GFP, a member of the large family of GTPases which cycles between the plasma membrane and early endosomes, to fluorescently label early endosomes. Using fluorescence microscopy and quantitative image analysis of cells expressing Rab5-GFP, we found that at early time points (t < 1 h), only a fraction (approximate to 35%) of RGD-tagged NPs (which target cell surface integrins) colocalize with wildtype EEs, independent of the NP\'s membrane charge density. In comparison, a GTP-hydrolysis deficient mutant, Rab5-Q79L, which extends the size and lifetime of EEs yielding giant early endosomes (GEEs), enabled us to resolve and localize individual NPs found within the GEE lumen. Remarkably, nearly all intracellular NPs are found to be trapped within GEEs implying little or no escape at early time points. The observed small degree of colocalization of NPs and wildtype Rab5 is consistent with recycling of Rab5-GDP to the plasma membrane and not indicative of NP escape from EEs.Taken together, our results show that endosomal escape of PEGylated nanoparticles occurs downstream of EEs i.e., from late endosomes/lysosomes. Our studies also suggest that Rab5-Q79L could be used in a robust imaging assay which allows for direct visualization of NP interactions with the luminal membrane of early endosomes. (C) 2015 Elsevier B.V. All rights reserved.
Live Cell Imaging of GFP-Rab Gtpases allows for Intracellular, Spatiotemporal Tracking of Surface Functionalized Lipid-DNA Complexes
(2013-01-29)
Majzoub, Ramsey N.
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Chan, Chia-Ling
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Ewert, Kai K.
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Liang, Keng S.
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Safinya, Cyrus R.
Live Cell Imaging with Rab-Gtpases Elucidates Intracellular Pathways of RGD and iRGD Tagged Cationic Lipid-DNA Nanoparticles
(2014-01-28)
Majzoub, Ramsey N.
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Ewert, Kai K.
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Kotamraju, Venkata R.
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Chan, Chia-Ling
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Liang, Keng S.
Optimizing cationic and neutral lipids for efficient gene delivery at high serum content
(2014-03-01)
Chan, Chia-Ling
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Ewert, Kai K.
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Majzoub, Ramsey N.
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Hwu, Yeu-Kuang
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Liang, Keng S.
BackgroundCationic liposome (CL)-DNA complexes are promising gene delivery vectors with potential application in gene therapy. A key challenge in creating CL-DNA complexes for application is that their transfection efficiency (TE) is adversely affected by serum. In particular, little is known about the effects of a high serum content on TE, even though this may provide design guidelines for application in vivo. MethodsWe prepared CL-DNA complexes in which we varied the neutral lipid [1,2-dioleoyl-sn-glycerophosphatidylcholine, glycerol-monooleate (GMO), cholesterol], the headgroup charge and chemical structure of the cationic lipid, and the ratio of neutral to cationic lipid; we then measured the TE of these complexes as a function of serum content and assessed their cytotoxicity. We tested selected formulations in two human cancer cell lines (M21/melanoma and PC-3/prostate cancer). ResultsIn the absence of serum, all CL-DNA complexes of custom-synthesized multivalent lipids show high TE. Certain combinations of multivalent lipids and neutral lipids, such as MVL5(5+)/GMO-DNA complexes or complexes based on the dendritic-headgroup lipid TMVLG3(8+) exhibited high TE both in the absence and presence of serum. Although their TE still dropped to a small extent in the presence of serum, it reached or surpassed that of benchmark commercial transfection reagents, particularly at a high serum content. ConclusionsTwo-component vectors (one multivalent cationic lipid and one neutral lipid) can rival or surpass benchmark reagents at low and high serum contents (up to 50%, v/v). We propose guidelines for optimizing the serum resistance of CL-DNA complexes based on a given cationic lipid. Copyright (c) 2014 John Wiley & Sons, Ltd.
Phase tomography reconstructed by 3D TIE in hard X-ray microscope
(2007)
Yin, Gung-Chian
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Chen, Fu-Rong
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Pyun, Ahram
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Ho, Jung
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Hwu, Yeukuang
X-ray phase tomography and phase imaging are promising ways of investigation on low Z material- A polymer blend of PE/PS sample was used to test the 3D phase retrieval method in the parallel beam illuminated microscope. Because the polymer sample is thick, the phase retardation is quite mixed and the image can not be distinguished when the 2D transport intensity equation (TIE) is applied. In this study, we have provided a different approach for solving the phase in three dimensions for thick sample. Our method involves integration of 3D TIE/Fourier slice theorem for solving thick phase sample. In our experiment, eight sets of de-focal series image data sets were recorded covering the angular range of 0 to 180 degree. Only three set of image cubes were used in 3D TIE equation for solving the phase tomography. The phase contrast of the polymer blend in 3D is obviously enhanced, and the two different groups of polymer blend can be distinguished in the phase tomography.
Quantitative phase retrieval in transmission hard x-ray microscope
(2007-04-30)
Yin, Gung-Chian
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Chen, Fu-Rong
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Hwu, Yeukuang
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Shieh, Han-Ping D.
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Liang, Keng S.
Quantitative phase retrieval with a sub-100-nm resolution is achieved from micrographs of a zone plate based transmission x-ray microscope. A plastic zone plate containing objects of sizes from micrometers down to tens of nanometers is used as a test sample to quantify the retrieved phase. Utilizing the focal serial images in the image plane, the phase information is retrieved quantitatively across the entire range of sizes by combining the transport intensity equation and self-consistent wave propagation methods in this partial coherence system. The study demonstrates a solution to overcome the deficiency encountered in the two phase retrieval approaches. (c) 2007 American Institute of Physics.
Rapid and sensitive detection of cancer cells by coupling with quantum dots and immunomagnetic separation at low concentrations
(2011-06-15)
Hsieh, Yi-Heui
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Lai, Lee-Jene
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Liu, Shih-Jen
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Liang, Keng S.
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電子物理學系
This work presents a rapid and sensitive method for detecting cancer cells at low concentration. In this method, two biomarkers of T-help cancer cells are detected simultaneously. One biomarker is conjugated with magnetic beads to separate T-help cell from the mixed cells and the other biomarker, associated with quantum dots, is used to detect fluorescence. The specific T-help cells can be quantified using the relationship between the QD fluorescence intensity and the cell frequency following magnetic separation. The intensity of fluorescence increases linearly with the frequency of T-help cells from 10(-7) to 10(-3), and neither B cells nor red blood cells interfere with the detection of T-help cells. Moreover, the total detection time is under 15 min, even though the frequency of specific T-help cells is as low as 5 x 10(-7). The numerous advantages of detecting specific cells at low concentration using the presented method include ease of preparation, low cost, fast detection, and high sensitivity. (C) 2011 Elsevier B.V. All rights reserved.
Simultaneous use of small- and wide-angle X-ray techniques to analyze nanometerscale phase separation in polymer heterojunction solar cells
(2008-07-02)
Chiu, Mao-Yuan
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Jeng, U-Ser
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Su, Chiu-Hun
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Liang, Keng S.
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Wei, Kung-Hwa
Using grazing-incidence small-angle X-ray scattering and wide-angle X-ray diffraction techniques to analyze the nanoscale phase separation of P3HT and PCBM after annealing, the effects of the sizes of the PCBM clusters and P3HT crystallites on the power conversion efficiency of bulk heterojunction solar cells are studied.
Size dependence of tetrahedral bond lengths in CdSe nanocrystals
(2007-04-16)
Wu, Pin-Jiun
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Stetsko, Yuri P.
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Tsuei, Ku-Ding
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Dronyak, Roman
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Liang, Keng S.
The structural characteristics of organically passivated CdSe nanocrystals (NCs) were investigated with x-ray diffraction and extended x-ray absorption fine structure. As the NC size decreases, the axial bond length R-(1) for an atomic tetrahedron extends but the equatorial bond length R-(2) contracts, with a similar tendency of distortion for the lattice parameters of the wurtzite structure. The authors suggest that the observed hexagonal distortion is attributed to the surface stress of the NCs related to the organic passivation effect and the relaxation of atomic positions at the stacking fault interface. (c) 2007 American Institute of Physics.
Strategies for optimizing lipid-based delivery of nucleic acids to cells for gene delivery and gene silencing: Synthesis, live cell imaging, and transfection efficiency studies
(2013-04-07)
Ewert, Kai K.
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Majzoub, Ramsey N.
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Chan, Chialing
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Liang, Keng S.
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Safinya, Cyrus R.
Strategies for optimizing lipid-based delivery of nucleic acids to cells for gene delivery and gene silencing: Synthesis, live cell imaging, and transfection efficiency studies
(2013-04-07)
Ewert, Kai K.
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Majzoub, Ramsey N.
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Chan, Chialing
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Liang, Keng S.
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Safinya, Cyrus R.
Structural evolution of poly(styrene-b-4-vinylpyridine) diblock copolymer/gold nanoparticle mixtures from solution to solid state
(2007-07-10)
Huang, Ching-Mao
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Wei, Kung-Hwa
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Jeng, U-Ser
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Liang, Keng S.
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材料科學與工程學系
We used in situ annealing small-angle X-ray scattering to monitor the structural evolution of a spherical poly(styrene-b-4-vinylpyridine) diblock copolymer (PS-b-P4VP)/2-phenylethanethiol-coated Au nanoparticle (AuSC2Ph) mixture in the solid state during its thermal annealing. We found that the Au nanoparticles (NPs) that existed initially in a random state with some cluster packing in the PS domain diffused to the interface of the amphiphilic PS-b-P4VP diblock copolymer within 4 h at 170 degrees C under vacuum to form NP-filled shell-like assemblies, as further evidenced from transmission electron microscopy imaging. From the X-ray photoelectron spectroscopy data, we speculate that this interfacial activity of AuSC2Ph results from the fact that the initially hydrophobic Au NP surfaces became increasingly hydrophilic as most of the 2-phenylethanethiol ligands had evaporated off. The Au NP nanoshell assemblies located at the interface between PS and P4VP were quite stable even after redissolving in toluene; they remained in the form of PS-Au-P4VP core/shell/corona onion micelles, as evidenced from solution state small-angle X-ray scattering data.
Surface-functionalized cationic liposome-DNA complexes: Strategies for optimal targetting and endosomal escape for gene delivery
(2012-03-25)
Safinya, Cyrus R.
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Majzoub, Ramsey N.
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Chan, Chialing
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Ewert, Kai K.
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Liang, Keng S.