bluuebunny/crossref_metadata_2025 huggingface dataset:
256×192 pixel field emitter array image sensor with high-gain avalanche rushing amorphous photoconductor target
Authors: Takiguchi Yoshiro , Nanba M. , Osada K. , Watabe T. , Okazaki S. , Egami N. , Tanioka K. , Tanaka M. , Itoh S.
Published: July 2004

A 256×192 pixel field emitter array (FEA) image sensor with a highly sensitive high-gain avalanche rushing amorphous photoconductor (HARP) target was fabricated and tested as a step toward the development of a practical image sensor for ultrahigh sensitivity and ultrahigh-definition compact TV cameras. The experimental results showed that the prototype had an adequate resolution corresponding to the spot size of the scanning electrons on the HARP target which was estimated by the simulation. The prototype also had a wide dynamic range and high sensitivity, demonstrating its potential as a next generation practical image sensor and offering new application of FEAs.
Real-time stress evolution during growth of InxAl1−xAs/GaAs metamorphic buffer layers
Authors: Lynch C. , Beresford R. , Chason E.
Published: July 2004

Real-time stress measurements during growth of both linearly and step-graded InxAl1−xAs/GaAs metamorphic buffer layers are presented. We show that in situ stress monitoring provides information about the evolution of the film stress and surface lattice parameter, the kinetics of which cannot be fully studied using ex situ analysis. This technique may be used to help optimize the design of metamorphic buffer layers.
Comparison of As- and P-based metamorphic buffers for high performance InP heterojunction bipolar transistor and high electron mobility transistor applications
Authors: Lubyshev D. , Fastenau J. M. , Fang X.-M. , Wu Y. , Doss C. , Snyder A. , Liu W. K. , Lamb M. S. M. , Bals S. , Song C.
Published: July 2004

Metamorphic buffers (M-buffers) consisting of graded InAlAs or bulk InP were employed for the production of InP-based epiwafers on GaAs substrates by molecular-beam epitaxy. The graded InAlAs is the standard for production metamorphic high electron mobility transistors (M-HEMTs), while the bulk InP offers superior thermal properties for higher current density circuits. The surface morphology and crystal structure of the two M-buffers showed different relaxation mechanisms. The graded InAlAs gave a cross-hatched pattern with nearly full relaxation and very effective dislocation filtering, while the bulk InP had a uniform isotropic surface with dislocations propagating further up towards the active layers. Both types of M-buffers had atomic force microscopy root-mean-square roughness values around 20–30 Å. The Hall transport properties of high electron mobility transistors (HEMTs) grown on the InAlAs M-buffer, and a baseline HEMT grown lattice matched on InP, both had room-temperature mobilities >10 000 cm2/V s, while the M-HEMT on the InP M-buffer showed a decrease to 9000 cm2/V s. Similarly, the dc parameters of a double heterojunction bipolar transistor (DHBT) grown on the InAlAs M-buffer were much closer to the baseline heterojunction bipolar transistor than a DHBT grown on the InP M-buffer. A high breakdown voltage of 11.3 V was achieved on an M-DHBT with the InAlAs M-buffer. We speculate that the degradation in device characteristics on the InP M-buffer was related to the incomplete dislocation filtering.
Useful protocol for evaluating subtle and important differences between photoresist formulations
Authors: Pawloski Adam R. , Nealey Paul F.
Published: July 2004

A useful protocol is presented for evaluation of the lithographic performance of chemically amplified photoresists that differ by formulation. A standard addition technique, infrared spectroscopy, and a development rate monitor were used, respectively, to measure the efficiency of photoacid generation upon exposure, the extent of polymer deprotection after the postexposure bake (PEB), and the dissolution rate of the resist in aqueous base developer. The combination of these experimental methods enabled the determination of (1) the concentration of photoacid that was generated in the resists as a function of exposure dose, (2) the extent of polymer deprotection that was achieved after the PEB as a function of the concentration of photoacid, and (3) the dissolution rate of the resist as a function of the extent of polymer deprotection. Photoresists may be compared using these three key relationships to evaluate the effects of formulation on resist performance. These methods were applied to investigate the impact of the chemical structure of two photoacid generators, norbornene dicarboximidyl triflate and triphenylsulfonium triflate, on the performance of photoresist comprised of poly(p-t-butoxycarbonyloxystyrene-co-p-hydroxystyrene) as the matrix polymer. The chemical structure of the photoacid generator affected the performance of these resist formulations in at least three key ways: (1) the efficiency of photoacid generation upon exposure to ionizing radiation, (2) the reaction-diffusion process of photoacid to deprotect the polymer during postexposure processing, and (3) the inhibition of resist dissolution in aqueous base. These three processes synergistically contributed to the sensitivity of the resist. The differences in the performance between these two resists were directly related to the chemical structure of the photoacid generator, in ways beyond the type of photogenerated acid, since both molecules produce triflic acid upon exposure and the matrix polymer and processing conditions were identical for both resist systems.
Selective growth of C60/GaAs and the optical characteristic
Authors: Ogawa Masaaki , Nishinaga Jiro , Kida Yosuke , Yamagata Hiroshi , Aihara Tomoyuki , Horikoshi Yoshiji
Published: July 2004

Area selective epitaxy of C60/GaAs heterostructures on GaAs substrates masked by SiO2 has been investigated by solid-source molecular beam epitaxy. The crystallinity of the C60/GaAs heterostructures on GaAs planer substrates during growth is evaluated by reflection high-energy electron diffraction. The surface morphology of the mask substrate is then elucidated by scanning electron microscopy. Finally, the optical characteristic and selectivity are evaluated by microphotoluminescence.
Combined x-ray diffraction/scanning tunneling microscopy study of segregation and interfacial bonding in type-II heterostructures
Authors: Zhong M. , Steinshnider J. , Weimer M. , Kaspi R.
Published: July 2004

Appropriate control over the type-II band alignment between InAs and GaSb is important for a number of applications, including the further development of midinfrared (IR) semiconductor lasers and long-wavelength photodetectors. Accurate tailoring of interface structure and composition in such heterostructures grown by molecular beam epitaxy is nevertheless problematic for several reasons. Special challenges are posed by antimony segregation at the arsenide-on-antimonide interface, indium segregation at the antimonide-on-arsenide interface, and by the desire to selectively control the purity and types of interface bonds at either heterojunction. Here, we briefly review how cross-sectional scanning tunneling microscopy may be used to examine antimony and indium segregation with atomic-scale precision in type-II quantum wells, and then explain how such measurements suggest a unique structural interpretation for the residual strain exhibited by typical mid-IR semiconductor laser active regions in x-ray diffraction.
Competition of nitrogen doping and graphitization effect for field electron emission from nanocrystalline diamond films
Authors: Karabutov A. V. , Konov V. I. , Pereverzev V. G. , Vlasov I. I. , Zavedeev E. V. , Pimenov S. M. , Loubnin E. N.
Published: July 2004

Field electron emission properties were investigated for nitrogen-doped nanocrystalline diamond films grown on Si substrates from CH4/Ar/N2 gas mixtures by direct current arc plasma chemical vapor deposition (CVD). Different nitrogen content in the gas mixtures and different deposition temperatures were used for the growth to get the films with different nitrogen content, microstructure, and field emission properties. In addition, higher growth temperature for some of the films assists to partial graphitization of the diamond films that can improve the emission too. The film surface and microstructure was studied using atomic force microscopy, scanning electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and electron energy-loss spectra to find correlations between the field emission and other film properties. The field electron emission was studied using both a macroscopic phosphor screen setup and a microprobe setup. It was found that nitrogenated CVD diamond films show different microstructure than the films prepared without nitrogen. The field electron emission for the nitrogenated films was typically better than for the “pure” diamond films. On the other hand, partially graphitized films grown at higher temperatures (with or without nitrogen in the gas mixtures) typically show the best field emission properties with emission threshold fields of as low as 1–2 V/μm, higher density of emission sites, and higher working limit of the emission current.
Secondary ion mass spectrometry analysis of vertical cavity surface-emitting lasers
Authors: Kim Yong K. , Choquette Kent D. , Baker Judith E. , Allerman Andrew A.
Published: July 2004

Depth profile analysis by high-resolution secondary ion mass spectrometry (SIMS) can accurately determine C and Si concentrations within monolithic reflectors of vertical cavity surface-emitting lasers (VCSELs). These SIMS depth profiles are quantified to atomic concentrations using relative sensitivity factors and calibration standards, and are correlated to the laser characteristics. We compare the light output versus current and voltage of a conventional oxide-confined VCSEL with a self-pulsating VCSEL. We show that SIMS depth profiling of VCSELs can be useful as a diagnostic method for VCSEL epitaxial wafers, and that the doping level of oxide aperture layers can dramatically impact the device performance.
Electron-beam lithography with aromatic self-assembled monolayers on silicon surfaces
Authors: Küller A. , El-Desawy M. A. , Stadler V. , Geyer W. , Eck W. , Gölzhäuser A.
Published: July 2004

Aromatic self-assembled monolayers are formed via the coupling of hydroxy head groups to hydrogen-terminated silicon surfaces. We first investigate the application of 4-hydroxy-1,1′-biphenyl as an ultrathin negative tone electron-beam (e-beam) resist using conventional e-beam lithography with a beam energy of 3 keV. We demonstrate the fabrication of nanometer silicon patterns that are transferred using the modified monolayer as a resist mask for a wet chemical etching process in potassium hydroxide. The necessary dose for complete cross linking was determined to be 20 mC/cm2. Using this approach, isolated silicon structures with lateral dimensions down to ∼10 nm and periodic structures with a resolution of ∼20 nm were fabricated. On the other hand, 4′-nitro-4-hydroxy-1,1′-biphenyl has been found not to form monolayers suitable for chemical lithography on hydrogenated silicon surfaces. Upon adsorption, the nitro groups are partially reduced to amino groups by the hydrogenated surface and some of the molecules bind to the surface via the nitrogen terminus.
Design of a complementary-metal-oxide-semiconductor-compatible field-emission magnetic sensor with adjustable sensitivity
Authors: Garner D. M. , French P. J. , Hui G. , Fung A.
Published: July 2004

We report on the development of a practical realization of a vacuum magnetic sensor device. The proposed device differs from those proposed in previous work [M. I. Marques, P. A. Sarena, D. Nicolaescu, and A. Correia, Solid-State Electron. 45, 977 (2001); K. Uemura, S. Kanemaru, and J. Itoh, J. Micromech. Microeng. 11, 81 (2001)] in that it is lateral, with the cathode, gate, and anode electrodes all lying in a plane parallel to that of the silicon substrate. By using the ion trajectory modeling program SIMION, we show that this structure allows the sensor device to have a variable sensitivity mode of operation, in which the sensitivity can be controlled through application of a voltage to the device substrate. This device allows a magnetic sensing system to be created that can measure magnetic field strengths over many orders of magnitude.
Quadrupole-mass-spectroscopy studies on hot-filament chemical vapor deposition of carbon films with nanosized constituents
Authors: Choi Seungho , Lee Soonil , Koh Ken Ha
Published: July 2004

We used a quadrupole mass spectrometer (QMS) to investigate the dissociation of source gases and the generation of radical species during the hot-filament chemical vapor deposition (HFCVD) process at various methane and ammonia concentrations. Since the HFCVD was carried out at the working pressure of 30 Torr, a capillary tube and a 5 μm pinhole were installed to sample the small amount of gas from the HFCVD chamber to the differentially pumped QMS at the vacuum level of 5×10−6 Torr. An investigation of the systematic variations in mass spectra corresponding to the increase of methane concentration in the ammonia-free source gases revealed substantial generation of chemical species containing two carbon atoms. However, an increase of ammonia concentration in the source gas with 20% of methane resulted in generation of nitrogen containing radicals such as CN and HCN, together with the suppression of two-carbon radicals. An implication of observed mass-spectrum variation for the growth behavior of carbon nanotube and/or carbon nanoparticle films was discussed.
Interference fringes observed in electron emission patterns of a multiwalled carbon nanotube
Authors: Hata Koichi , Takakura Akihiro , Miura Kenji , Ohshita Akinori , Saito Yahachi
Published: July 2004

A capped multiwalled carbon nanotube with clean surface gives field emission patterns consisting of six pentagonal rings which correspond to pentagons located at the tip end. One or a few bright streaks are also observed at the boundaries of neighboring pentagons. The spacing of streaks is inversely proportional to the square root of the accelerating voltage. Namely, the spacing changes with the wavelength of emitted electrons according to Young’s interference equation. The visibility of streaks increased with the accelerating voltage, which can be explained in terms of a concept of a virtual source size. These experimental results suggest that the streaks are no more than Young’s interference fringes for which the adjacent pentagons behave as double slits.
Conductivity change of carbon nanotube with strong electron-donating and withdrawing molecules
Authors: Oh Jihoon , Roh Seungkwang , Yi Whikun , Lee Haesung , Yoo Jibeom
Published: July 2004

Electron transport properties of single-walled carbon nanotubes are investigated with TTF and TCNQ molecules, i.e., tetrathiafulvalene and 7,7,8,8-tetracyano-p-quinodimethane. TTF and TCNQ are well known strong charge transfer molecules. From the current–voltage measurement in a vacuum, current decreases and increases distinctly upon the adsorption of TTF and TCNQ, respectively. The same results are observed in the case of MAT–single-walled carbon nanotube (SWNT) device, representing a good prospect for future nanostructured devices using carbon nanotubes, especially as chemical sensors. According to the spectroscopic data from x-ray spectroscopy and near infrared spectroscopy, the adsorbed TTF and TCNQ molecules act as electron-donating and withdrawing species, respectively, on the surface of SWNTs.
Schottky emitter using boron-doped diamond
Authors: Bae Joon Hyung , Minh Phan Ngoc , Ono Takahito , Esashi Masayoshi
Published: July 2004

In this article, a microboron-doped diamond Schottky emitter for microelectron sources is presented. We fabricated an emitter tip on the top of the cantilever-type heating element using selective diamond deposition and silicon molding techniques. The fabricated diamond emitter shows high brightness emission current of 800 nA at a tip-anode (screen) electric field of 0.55 V/μm and tip heating voltage of 25 V. From the estimation using the Schottky emission model, the temperature of the emitter was found out 862±10 °C. The long-term stability of the emission current was characterized. This kind of structure can be utilized for electron sources with potential advantages of low threshold voltage and long lifetime stability in the proper emission condition.
Interface bonding structure of hafnium oxide prepared by direct sputtering of hafnium in oxygen
Authors: Wong Hei , Ng K. L. , Zhan Nian , Poon M. C. , Kok C. W.
Published: July 2004

The interface properties of the hafnium gate oxide films prepared by direct sputtering of hafnium in oxygen with rapid thermal annealing have been investigated in detail. X-ray photoelectron spectroscopy reveals that the interface silicate layer is a random mixture of Hf–O, Si–O, Hf–Si, and excess Hf and Si atoms. The contributions of these bonds to the composition of silicate layer are governed by the Si/Hf ratio. At low Si/Hf ratio (<2), the silicate layer is a mixture of SiO4 and HfO4 phases. At higher Si/Hf ratio (2–5), the contribution of the HfO4 phase decreases and Hf–Si (silicide) bonds become important. At very high Si/Hf ratio (>9) and close to the substrate, Hf–Si dominates and the high strain Hf–Si bonds govern the electrical properties of the interface. These results explain the observed high interface trap density at the HfO2/Si interface and the soft breakdown behavior which is different from the silicon oxide film.
Photoconductive characteristics in a trench-type InGaAs quantum-wire field effect transistor
Authors: Jang Kee-Youn , Sugaya Takeyoshi , Hahn Cheol-Koo , Ogura Mutsuo , Komori Kazuhiro , Shinoda Akito , Yonei Kenji
Published: July 2004

We describe the photoconductive characteristics of a narrow trench-type InGaAs quantum wire field effect transistor (QWR-FET) with a negative differential resistance (NDR). The photoconductive intensity peak of the trench-type QWR was observed at a drain voltage (VDS) region lower than an onset voltage of NDR (VNDR), and decreased at the VDS larger than the VNDR. This result indicates that the carriers transfer from the QWR level to other quantum levels at the VDS region larger than the VNDR. By numerically solving the two-dimensional single band Schrödinger equation using the finite element method, we confirm that the carrier can transfer from the high mobility QWR layer to the low mobility sidewall quantum wells, which is thought to be a mechanism of the negative differential resistance of the QWR-FETs.
Flux profile modeling: Monte Carlo simulation and numerical computation
Authors: Venkat Rama , Pemmireddy Bharat Reddy , Vijayagopal Ramprasad , Cheng Hwa , Bresnahan Rich
Published: July 2004

Spatial variations in flux are a result of the shape of the Knudsen cell crucible (K-cell) and the geometry of the growth chamber. In this article, a process simulation tool based on a phenomenological model is proposed and elaborated. Two different models based on physical principles are investigated. Model I includes the primary flux from the liquid surface and a secondary flux re-emitted from the crucible walls for the total flux at the platen. No intermolecular collisions are considered in this model. Since the investigated 10000 g SUMO crucible has a tapered region leading to the crucible opening (the smallest radii opening), molecules undergo extensive interwall and intermolecular collisions in that region. The simulation of intermolecular collisions requires considerable time and limits the usage of the modeling tool in the industry. Thus, the effect of intermolecular collisions is captured through the assumption of a virtual flux source (VFS) at the neck in model II. For the two models, a Monte Carlo approach and a numerical approach are employed for theoretical analysis. The Monte Carlo and numerical approaches as implemented are equivalent and produce essentially the same results. The results of model II from both approaches using cos2 θ distribution from the VFS best describes the experimental data for the SUMO 10000 g crucible. Further comparison with experimental data is necessary to validate the cos2 θ model.
Similarities between Ga0.48In0.52NyP1−y and Ga0.92In0.08NyAs1−y grown on GaAs (001) substrates
Authors: Hong Y. G. , Nishikawa A. , Tu C. W.
Published: July 2004

Bulk Ga0.48In0.52NyP1−y and Ga0.92In0.08NyAs1−y were grown on GaAs (001) substrates by gas-source molecular beam epitaxy. Optical and electrical transport properties show great similarities between Ga0.48In0.52NyP1−y and Ga0.92In0.08NyAs1−y. With nitrogen incorporation, the low-temperature photoluminescence (PL) spectra exhibit an asymmetric line shape with a low-energy tail indicating the presence of N-related localized states which dominate the radiative recombination processes. N incorporation significantly reduces the electron mobility and electron concentration. Because N is more electronegative than P or As, N has a tendency to bind the free valence electron of Si. The free electron concentration of N-containing Ga0.48In0.52N0.005P0.995 and Ga0.48In0.52N0.03As0.97 decreases dramatically with high-temperature annealing because Si is passivated by N through the formation of Si–N pairs.
Molecular-beam epitaxy growth of quantum cascade lasers on (111)B substrates for second harmonic generation
Authors: Marcadet X. , Ortiz V. , Bengloan J.-Y. , Dhillon S. , Calligaro M. , Sirtori C.
Published: July 2004

The growth conditions for realizing quantum cascade lasers on (111)B tilted GaAs substrates by molecular beam epitaxy are analyzed. AlGaAs/GaAs(111)B unipolar lasers emitting at 11.5 μm are fabricated and show encouraging performances which allow the nonlinear susceptibility of bulk GaAs to be exploited. The emission of coherent light at 5.75 μm is obtained by intracavity frequency doubling. Frequency doubling in quantum cascade lasers on (111) oriented substrates is very attractive and can be an alternative way to access the short mid-infrared wavelength region (3–4 μm).
Fabrication of three-dimensional microstructures using standard ultraviolet and electron-beam lithography
Authors: Galas J. C. , Belier B. , Aassime A. , Palomo J. , Bouville D. , Aubert J.
Published: July 2004

We have designed and fabricated shape-controlled three-dimensional structures combining electron- beam and ultraviolet (UV) lithography. Starting with a tiff file format, a gray scale pattern using a high energy beam sensitive mask is produced with electron-beam direct writing. In only a one step UV exposure, an optical lens and a photonic band gap structure in 16.5 μm thick AZ 4562 positive photoresist, with controlled profile and smooth resist surface, were fabricated. A three-dimensional grid structure was also transferred to a 100 μm thick SU-8 negative photoresist.
Simulation of field-emitted electron trajectories and transport from carbon nanotubes
Authors: Walker D. G. , Zhang W. , Fisher T. S.
Published: July 2004

Carbon nanotubes exhibit excellent field-emission behavior characterized by low turn-on fields and large current densities. The present work investigates the transport of electrons by field emission and the resulting spatial distribution at the anode surface through simulation of the tunneling process and the trajectory of electrons across the vacuum gap. Beam spreading is characterized by a multidimensional potential, Coulomb interaction, and randomized energy distributions for closed and open single-walled nanotubes. Electron trajectories are determined by Monte Carlo simulation. Results indicate that the electron beam spreads primarily due to local field curvature near the emission site and that, for some nanotubes, a ring pattern at the anode is created. The ring diameter at the anode spreads by 1.2 μm per 10 μm of vacuum gap for the low currents (<100 μA) considered in this work. These results are consistent with experimental observations.
Rapid repair of plasma ash damage in low-k dielectrics using supercritical CO2
Authors: Gorman B. P. , Orozco-Teran R. A. , Zhang Z. , Matz P. D. , Mueller D. W. , Reidy R. F.
Published: July 2004

Plasma damage to methylsilsequioxane (MSQ) based low-k dielectrics degrades the material’s resistance to subsequent wet etch processes. In addition, the loss of methyl species during plasma exposure increases their susceptibility to water absorption leading to increased dielectric permittivities. In this article, we introduce a process in which silylating agents dissolved in supercritical CO2 are used to functionalize ash-damaged surfaces. This silylation process greatly decreases the time necessary to induce hydrophobicity (less than 1 min as determined by a change in contact angle from 18° to 90°). The process also reduces the concentration of reactive silylation agents needed for full hydrophobicity to less than 1 vol %. Further, this process is also shown to reduce material loss during subsequent wet etch processes. Film thickness measured by scanning electron microscopy before and after treatment illustrates a difference of approximately 0.1 μm after etching in a dilute HF solution for 30 s.
Electron emission from heavily nitrogen-doped heteroepitaxial chemical vapor deposition diamond
Authors: Okano Ken , Mine Takuya , Saito Ichitaro , Yamaguchi Hisato , Yamada Takatoshi , Sawabe Atsuhito
Published: July 2004

Heavily nitrogen (N)-doped polycrystalline diamond was reported to have excellent electron emission properties. One of the obstacles to practical application of this diamond was its localized and uncontrolled electron emission site. Even though we have reported the broad area electron emission from homoepitaxial diamond in our previous work, the difficulty remained to fabricate the injection contact for homoepitaxial diamond because its substrate is an insulator, which is not suitable for practical applications. In this study, we have obtained heavily N-doped heteroepitaxial diamond films on Iridium (Ir), and its electron emission properties are investigated. It is found that the emission threshold voltage of heteroepitaxial diamond (100) is higher than that of other heavily N-doped diamonds and has linear relationship between the spacing as is not observed in metal–insulator–vacuum type emission, which is a model proposed for electron emission from polycrystalline and homoepitaxial diamonds. From the characterization results, obtained film is confirmed to be identical to heavily N-doped polycrystalline and homoepitaxial diamond. The difference in the emission properties, thus, is caused by high electron affinity of diamond (100) and the absence of negative charges at the Ir/diamond interface.
Diversification of Ig Superfamily Genes in an Invertebrate
Authors: Zhang Si-Ming , Adema Coen M. , Kepler Thomas B. , Loker Eric S.
Published: July 2004

The freshwater snail
Biomphalaria glabrata
possesses a diverse family of fibrinogen-related proteins (FREPs), hemolymph polypeptides that consist of one or two amino-terminal immunoglobulin superfamily (IgSF) domains and a carboxyl-terminal fibrinogen domain. Here, we show that the IgSF1 domain of the
FREP3
subfamily is diversified at the genomic level at higher rates than those recorded for control genes. All sequence variants are derived from a small set of nine source sequences by point mutation and recombinatorial processes. Diverse
FREP3
transcripts are also produced. We hypothesize a mechanism present in snails that is capable of diversifying molecules involved in internal defense.
Tryptophan Hydroxylase-2 Controls Brain Serotonin Synthesis
Authors: Zhang Xiaodong , Beaulieu Jean-Martin , Sotnikova Tatyana D. , Gainetdinov Raul R. , Caron Marc G.
Published: July 2004

Dysregulation of brain serotonin contributes to many psychiatric disorders. Tryptophan hydroxylase-2 (Tph2), rather than Tph1, is preferentially expressed in the brain. We report a functional (C1473G) single-nucleotide polymorphism in mouse Tph2 that results in the substitution of Pro
447
with Arg
447
and leads to decreased serotonin levels in PC12 cells. Moreover, in BALB/cJ and DBA/2 mice that are homozygous for the 1473G allele, brain serotonin tissue content and synthesis are reduced in comparison to C57Bl/6 and 129X1/SvJ mice that are homozygous for the 1473C allele. Our data provide direct evidence for a fundamental role of Tph2 in brain serotonin synthesis.
Exploiting Tolerance Processes in Transplantation
Authors: Waldmann Herman , Cobbold Stephen
Published: July 2004

The full potential of organ transplantation has not yet been realized because of the hazards associated with the long-term use of immunosuppressive drugs. Modern research into mechanisms of immune tolerance offers the promise of reprogramming the immune system, so as to harness the body's natural tolerance mechanisms in the service of graft acceptance. This would allow the minimization of immunosuppressive treatment and offers the prospect of eventually weaning transplant recipients off their drugs.
Enzyme-Linked Immunosorbent Assays Using Recombinant Envelope Protein Expressed in COS-1 and
Drosophila
S2 Cells for Detection of West Nile Virus Immunoglobulin M in Serum or Cerebrospinal Fluid
Authors: Muerhoff A. Scott , Dawson George J. , Dille Bruce , Gutierrez Robin , Leary Thomas P. , Gupta Malini C. , Kyrk Charles R. , Kapoor Hema , Clark Patricia , Schochetman Gerald , Desai Suresh M.
Published: July 2004

Humans infected with West Nile virus (WNV) develop immunoglobulin M (IgM) antibodies soon after infection. The microtiter-based assays for WNV IgM antibody detection used by most state public health and reference laboratories utilize WNV antigen isolated from infected Vero cells or recombinant envelope protein produced in COS-1 cells. Recombinant antigen produced in COS-1 cells was used to develop a WNV IgM capture enzyme immunoassay (EIA). A supplementary EIA using WNV envelope protein expressed in
Drosophila melanogaster
S2 cells was also developed. Both assays detected WNV IgM in the sera of experimentally infected rhesus monkeys within approximately 10 days postinfection. Human sera previously tested for WNV IgM at a state public health laboratory (SPHL) were evaluated using both EIAs. Among the sera from 20 individuals with laboratory-confirmed WNV infection (i.e., IgM-positive cerebrospinal fluid [CSF]) that were categorized as equivocal for WNV IgM at the SPHL, 19 were IgM positive and one was negative by the new EIAs. Of the 19 IgM-positive patients, 15 were diagnosed with meningitis or encephalitis; the IgM-negative patient was not diagnosed with neurological disease. There was 100% agreement between the EIAs for the detection of WNV IgM. CSF samples from 21 individuals tested equivocal for WNV IgM at the SPHL; all 21 were positive in both bead assays, and 16 of these patients were diagnosed with neurological disease. These findings demonstrate that the new EIAs accurately identify WNV infection in individuals with confirmed WNV encephalitis and that they exhibit enhanced sensitivity over that of the microtiter assay format.
Characterization of Immunodominant Linear B-Cell Epitopes on the Carboxy Terminus of the Rinderpest Virus Nucleocapsid Protein
Authors: Choi Kang-Seuk , Nah Jin-Ju , Ko Young-Joon , Kang Shien-Young , Yoon Kyoung-Jin , Joo Yi-Seok
Published: July 2004

The nucleocapsid (N) protein of rinderpest virus (RPV) is one of the most abundant and immunogenic viral proteins expressed during natural or experimental infection. To identify immunogenic epitopes on the N protein, different forms of RPV N protein, including the full-length protein (N
1-525
), an amino-terminal construct (N
1-179
), and a carboxy-terminal construct (N
414-496
), were expressed in
Escherichia coli
as glutathione
S
-transferase (GST) fusion proteins. The antigenicity of each recombinant protein was evaluated by Western immunoblotting. All recombinants were recognized by hyperimmune RPV bovine antisera, indicating that immunoreactive epitopes may be present at both ends of the N protein. However, GST-N
414-496
was much more antigenic than GST-N
1-179
when tested with sera from vaccinated cattle, suggesting that an immunodominant or highly immunogenic epitope(s) may be located at the carboxy terminus of the N protein. Epitope mapping with overlapping peptides representing different regions of the carboxy terminus (amino acids 415 to 524) revealed three nonoverlapping antigenic sites in regions containing the residues
440
VPQVRKETRASSR
452
(site 1),
479
PEADTDPL
486
(site 2), and
520
DKDLL
524
(site 3). Among these, antigenic site 2 showed the strongest reactivity with hyperimmune anti-RPV bovine sera in a peptide enzyme-linked immunosorbent assay but did not react with hyperimmune caprine sera raised against peste-des-petits-ruminants virus, which is antigenically closely related to RPV. Identification of an immunodominant linear antigenic site at the carboxy terminus of the N protein may provide an antigen basis for designing diagnostics specific for RPV.
Bifidobacterial Species Differentially Affect Expression of Cell Surface Markers and Cytokines of Dendritic Cells Harvested from Cord Blood
Authors: Young Sarah L. , Simon Mary A. , Baird Margaret A. , Tannock Gerald W. , Bibiloni Rodrigo , Spencely Kate , Lane Juliette M. , Fitzharris Penny , Crane Julian , Town Ian , Addo-Yobo Emmanuel , Murray Clare S. , Woodcock Ashley
Published: July 2004

The gut microbiota may be important in the postnatal development of the immune system and hence may influence the prevalence of atopic diseases. Bifidobacteria are the most numerous bacteria in the guts of infants, and the presence or absence of certain species could be important in determining the geographic incidence of atopic diseases. We compared the fecal populations of bifidobacteria from children aged 25 to 35 days in Ghana (which has a low prevalence of atopy), New Zealand, and the United Kingdom (high-prevalence countries). Natal origin influenced the detection of bifidobacterial species in that fecal samples from Ghana almost all containedBifidobacterium infantiswhereas those of the other children did not. Choosing species on the basis of our bacteriological results, we tested bifidobacterial preparations for their effects on cell surface markers and cytokine production by dendritic cells harvested from cord blood. Species-specific effects on the expression of the dendritic-cell activation marker CD83 and the production of interleukin-10 (IL-10) were observed. Whereas CD83 expression was increased and IL-10 production was induced byBifidobacterium bifidum,Bifidobacterium longum, andBifidobacterium pseudocatenulatum,B. infantisfailed to produce these effects. We concluded thatB. infantisdoes not trigger the activation of dendritic cells to the degree necessary to initiate an immune response but thatB. bifidum,B. longum, andB. pseudocatenulatuminduce a Th2-driven immune response. A hypothesis is presented to link our observations to the prevalence of atopic diseases in different countries.
Cholera Toxin B-Subunit Gene Enhances Mucosal Immunoglobulin A, Th1-Type, and CD8+Cytotoxic Responses When Coadministered Intradermally with a DNA Vaccine
Authors: Sanchez Alba E. , Aquino Guillermo , Ostoa-Saloma Pedro , Laclette Juan P. , Rocha-Zavaleta Leticia
Published: July 2004

A plasmid vector encoding the cholera toxin B subunit (pCtB) was evaluated as an intradermal genetic adjuvant for a model DNA vaccine expressing the human papillomavirus type 16 L1 capsid gene (p16L1) in mice. p16L1 was coadministered with plasmid pCtB or commercial polypeptide CtB as a positive control. Coadministration of pCtB induced a significant increment of specific anti-L1 immunoglobulin A (IgA) antibodies in cervical secretions (P< 0.05) and fecal extracts (P< 0.005). Additionally, coadministration of pCtB enhanced the production of interleukin-2 and gamma interferon by spleen cells but did not affect the production of interleukin-4, suggesting a Th1-type helper response. Furthermore, improved CD8+T-cell-mediated cytotoxic activity was observed in mice vaccinated with the DNA vaccine with pCtB as an adjuvant. This adjuvant effect was comparable to that induced by the CtB polypeptide. These results indicate that intradermal coadministration of pCtB is an adequate means to enhance the mucosa-, Th1-, and CD8+-mediated cytotoxic responses induced by a DNA vaccine.
Eucaryotic Expression of the Nucleocapsid Protein Gene of Porcine Circovirus Type 2 and Use of the Protein in an Indirect Immunofluorescence Assay for Serological Diagnosis of Postweaning Multisystemic Wasting Syndrome in Pigs
Authors: Racine Sébastien , Kheyar Ali , Gagnon Carl A. , Charbonneau Benoît , Dea Serge
Published: July 2004

The purpose of this study was to develop a sensitive, rapid, and inexpensive immunofluorescence assay (IFA) using a recombinant porcine circovirus type 2 (PCV2) nucleocapsid protein for the serological detection of PCV2-specific antibodies in pig sera. The viral nucleocapsid protein encoded by the PCV2 ORF2 gene has recently been identified as the most immunoreactive viral protein that carries type-specific antigenic determinants. The ORF2 sequence of the IAF-2897 strain of PCV2 has been cloned into a pCEP5 eucaryotic expression vector under the control of the cytomegalovirus promoter, downstream of a polyhistidine sequence tag. The recombinant plasmid was used in transfection experiments with human epithelial kidney 293 cells that were further tested, and positive expression of the viral nucleocapsid protein was confirmed by IFA and Western blotting. Strong, specific fluorescence was observed in the nuclei of transfected cells. Test specificity to PCV2 was verified with several related infectious agents. Sensitivity was compared to that of standard IFA using PCV2-infected cells by evaluating the reactivities of 44 field serum samples from pigs on farms with a porcine population suffering from postweaning multisystemic wasting syndrome. The recombinant nucleocapsid-based test was able to detect 15 more positive-testing pigs than the PCV2-based IFA. Therefore, the relative sensitivity of the latter test was estimated at only 57.1% compared to that of the recombinant nucleocapsid-based test. The recombinant fusion protein has been purified by affinity chromatography and is being used to develop further sensitive serological tests.
Use of Bispecific Antibodies in Molecular Velcro Assays Whose Specificity Approaches the Theoretical Limit of Immunodetection for
Bordetella pertussis
Authors: Tang X. L. , Peppler M. S. , Irvin R. T. , Suresh M. R.
Published: July 2004

A bispecific monoclonal antibody (bsMAb) that detects
Bordetella pertussis
, the causative agent of whooping cough, and horseradish peroxidase (HRPO) has been developed by use of the quadroma technology. A quadroma, P123, was produced by fusing two well-characterized hybridomas against the bacterium and the enzyme and was subcloned to obtain a stable bsMAb-secreting cell line. The quadroma was theoretically expected to produce up to 10 different molecular species of immunoglobulins, so secreted bispecific antibody was complexed with excess HRPO and the HRPO-bsMAb complex was purified in one step by benzhydroxamic acid-agarose affinity cochromatography. An ultrasensitive homosandwich molecular “velcro” enzyme-linked immunosorbent assay for the detection of
B. pertussis
whole bacteria with HRPO-bsMAb was established in both microplate and nasopharyngeal swab formats. This assay demonstrates a high sensitivity that approaches the theoretical limit of detection of one bacterium. This new nanoprobe can be used to develop a new generation of assays that are simple, inexpensive alternatives to quantitative PCR and that can be used by clinical laboratories. This strategy of homosandwich assays with solid-phase monospecific antibodies and solution-phase bsMAb with specificity for the same repeating surface determinants can be applied to generate ultrasensitive immunodiagnostic assays for viruses and bacteria.
Association between Familial Deficiency of Mannose-Binding Lectin and Mutations in the Corresponding Gene and Promoter Region
Authors: Salimans M. M. M. , Bax W. A. , Stegeman F. , van Deuren M. , Bartelink A. K. M. , van Dijk H.
Published: July 2004

In a recent report, our group presented clinical research data supporting the role of mannose-binding lectin (MBL) deficiency in susceptibility to meningococcal disease (W. A. Bax, O. J. J. Cluysenaer, A. K. M. Bartelink, P. C. Aerts, R. A. B. Ezekowitz, and H. van Dijk, Lancet354:1094-1095, 1999). This association was reported earlier by Hibberd et al. (M. L. Hibberd, M. Sumiya, J. A. Summerfield, R. Booy, M. Levin, and the Meningococcal Research Group, Lancet353:1049-1053, 1999) but was not based on family data. Our study included three members of one family who had acquired meningococcal meningitis in early adulthood. The objective of the present study was to investigate whether the genotypes of the MBL gene in this family, analyzed by PCR, correlate with MBL concentrations. We found that genotype variants in the MBL gene and promoter region match the low functional MBL levels (<0.25 μg of equivalents/ml) in the sera of the three patients in this family and that a significant correlation between genotype MBL deficiency and meningococcal disease existed.
Evaluation of the Binax NOW, BD Directigen, and BD Directigen EZ Assays for Detection of Respiratory Syncytial Virus
Authors: Ohm-Smith Marilyn J. , Nassos Patricia S. , Haller Barbara L.
Published: July 2004

The Binax NOW assay (Binax, Inc., Portland, Maine) and the BD Directigen EZ assay (Becton Dickinson and Company, Sparks, Md.), two new rapid immunoassays for detection of respiratory syncytial virus (RSV), as well as the BD Directigen RSV assay (DRSV) (Becton Dickinson and Company) and direct immunofluorescence staining (DFA) were compared with culture for detection of RSV in fresh specimens from both children and adults during the 2002-2003 respiratory virus season. The majority (95%) of specimens were nasal or nasopharyngeal washes or aspirates. A total of 47 (26%) were culture positive for RSV. The overall sensitivities of DFA (
n
= 149), NOW (
n
= 118), EZ (
n
= 88), and DRSV (
n
= 180) compared with culture (
n
= 180) were 93, 89, 59, and 77%, respectively. The specificities of DFA, NOW, EZ, and DRSV were 97, 100, 98, and 96%, respectively. However, when results were separated into those from children and those from adults, DFA was the only rapid test adequate for detection of RSV (sensitivity of 100% compared to 0, 0, and 25% for NOW, EZ, and DRSV, respectively) in adults. For children the sensitivities of DFA, NOW, EZ, and DRSV were 93, 94, 72, and 81%. The NOW assay was the most sensitive and specific and the easiest to perform of the kit tests for detecting RSV in children. None of these three rapid kit tests was sensitive for detecting RSV in specimens from adults. DFA remains the rapid method of choice for detecting RSV in the adult population.
Highly Sensitive Assay for Detection of Enterovirus in Clinical Specimens by Reverse Transcription-PCR with an Armored RNA Internal Control
Authors: Beld Marcel , Minnaar René , Weel Jan , Sol Cees , Damen Marjolein , van der Avoort Harry , Wertheim-van Dillen Pauline , van Breda Alex , Boom René
Published: July 2004

The objective of the present study was the development of a diagnostic reverse transcription (RT)-PCR for the specific detection of enterovirus (EV) RNA in clinical specimens controlled by an internal control (IC) RNA. The IC RNA contains the same primer binding sites as EV RNA but has a different probe region. The IC RNA was packaged into an MS2 phage core particle (armored) and was added to the clinical sample to allow monitoring of both extraction efficiency and RT-PCR efficiency. Serial dilutions of the IC RNA were made, and the detection limit of the RT-PCR was tested in a background of EV RNA-negative cerebrospinal fluid. The sensitivity and specificity of the RT-PCR assay were tested by using all 64 known EV serotypes, several non-EV serotypes, and two Quality Control for Molecular Diagnostics (QCMD) Program EV proficiency panels from 2001 and 2002. In total, 322 clinical specimens were tested by RT-PCR, and to establish the clinical utility of the RT-PCR, a comparison of the results of viral culture and RT-PCR was done with 87 clinical specimens. The lower limit of sensitivity was reached at about 150 copies of IC RNA/ml. All 64 EV serotypes were positive, while all non-EV serotypes were negative. All culture-positive samples of the 2001 QCMD proficiency panel (according to the 50% tissue culture infective doses per milliliter) were positive by RT-PCR. Invalid results, i.e., negativity for both EV RNA and IC RNA, due to inhibition of RT-PCR were observed for 33.3% of the members of the 2002 QCMD proficiency panel and 3.1% of the clinical specimens. Inhibition of RT-PCR could be relieved by the addition of 400 ng of bovine α-casein per μl to both the RT reaction mixture and the PCR mixture. With this optimized protocol, the results for all samples of the 2002 QCMD proficiency panel and all clinical specimens except one fecal sample (0.3%) were valid. Evaluation of the clinical samples demonstrated that EV infection could be detected in 12 of 87 samples (13.8%) by RT-PCR, while viral culture was negative. Our data show that the RT-PCR with armored IC RNA offers a very reliable and rapid diagnostic tool for the detection of EV in clinical specimens and that the addition of bovine α-casein relieved inhibition of the RT-PCR for 99.7% of clinical specimens.
Comparative Evaluation of the New Version of the INNO-LiPA Mycobacteria and GenoType Mycobacterium Assays for Identification of
Mycobacterium
Species from MB/BacT Liquid Cultures Artificially Inoculated with Mycobacterial Strains
Authors: Padilla Eduardo , González Victoria , Manterola Jose María , Pérez Andrés , Quesada María Dolores , Gordillo Sergio , Vilaplana Cristina , Pallarés María Angeles , Molinos Sonia , Sánchez María Dolores , Ausina Vicente
Published: July 2004

The performance of two DNA line probe assays, a new version of INNO-LiPA Mycobacteria (Innogenetics, Ghent, Belgium) and the GenoType Mycobacterium (Hain Diagnostika, Nehren, Germany), were evaluated for identification of mycobacterial species isolated from liquid cultures. Both tests are based on a PCR technique and designed for simultaneous identification of different mycobacterial species by reverse hybridization and line probe technology. The INNO-LiPA Mycobacteria v2 targeting the 16S-23S rRNA gene spacer region was developed for the simultaneous identification of 16 different mycobacterial species. The GenoType Mycobacterium, which targets the 23S rRNA gene, allows simultaneous identification of 13 mycobacterial species. Both tests were evaluated on 110 mycobacterial strains belonging to 22 different mycobacterial species (20 reference strains, 83 clinical strains, and 4
Mycobacterium kansasii
strains isolated from tap water) that were previously inoculated into MB/BacT bottles. The sensitivity of both methods, defined as the number of positive results obtained with the
Mycobacterium
genus probe together with an interpretable result on the number of samples tested was 110 of 110 (100%) for INNO-LiPA and 102 of 110 (92.7%) for GenoType. For samples with interpretable results, INNO-LiPA was able to correctly identify 109 of 110 samples (99.1%), whereas the GenoType correctly identified 100 of 102 samples (98.0%). Both tests were easy to perform, rapid, and reliable when applied to mycobacterial identification directly from MB/BacT bottles.