The recombinant nucleocapsid (rN) protein of the coronavirus (CoV) responsible for severe acute respiratory syndrome (SARS) was cloned and expressed in Escherichia coli, extracted from cell lysates containing 6M urea, then purified by Ni(2+)-affinity chromatography. In animal immunogenicity studies, we found that most anti-rN protein antibodies were IgG2a in BALB/c mice vaccinated with rN emulsified in Montanide ISA-51 containing the synthetic oligodeoxynucleotide, CpG. In contrast, anti-rN protein antibodies of mice immunized with rN protein in PBS were found to mainly be IgG1. These results indicated that ISA-51/CpG-formulated rN protein was dramatically biased toward a Th1 immune response. To identify the B-cell immunodominant epitopes of the rN protein in the mouse and monkey, the reactivities of antisera raised against purified rN proteins formulated in ISA-51/CpG were tested with a panel of overlapping synthetic peptides covering the entire N protein sequence. Three immunodominant linear B-cell epitope regions were mapped to residues 166-180, 356-375, and 396-410 of the rN protein. When the reactivities of these peptides were screened with human sera from five SARS patients, peptides corresponding to residues 156-175 reacted strongly with sera from two of the SARS patients. These results indicated that the region around residues 156-175 of the N protein is immunogenic in the mouse, monkey, and human. We found that peptides corresponding to residues 1-30, 86-100, 306-320, and 351-365 contained murine immunodominant T-cell epitopes. To identify functional CTL epitopes of the N protein, BALB/c mice were immunized with peptides containing the H-2K(d) CTL motif emulsified in adjuvant ISA-51/CpG. Using an IFN-gamma secretion cell assay and analysis by flow cytometry, peptides containing residues 81-95 were found to be capable of stimulating both CD4(+) and CD8(+) cell proliferation in vitro. We also only observed that peptides corresponding to residues 336-350 were capable of stimulating IFN-gamma production in T-cell cultures derived from peripheral blood mononuclear cells (PBMCs) of macaques immunized with the rN protein emulsified in ISA/CpG adjuvant. Our current results together with those of others suggest that some immunodominant B-cell and T-cell epitopes are conserved in the mouse, monkey, and human. This information is very important for the development SARS diagnostic kits and a vaccine.
In this work, a single-crystalline β-Ga2O3 epilayer was grown on (0001) sapphire at low temperature by low-pressure metal organic chemical vapor deposition. The optimized parameters for the chamber pressure, oxygen flow, and growth temperature were 15 Torr, 200 sccm, and 500 °C, respectively. The β-Ga2O3 epilayer was fabricated as a metal-semiconductor-metal solar-blind deep ultraviolet photodetector. Due to the gallium oxide grown at low temperature, the as-grown β-Ga2O3 epilayer was annealed at 800 °C in atmosphere or in a nitrogen environment. The effects of defects of the β-Ga2O3 epilayer before and after N2 annealing were studied using x-ray diffraction system, cathodoluminescence at differential temperature, and Hall measurement. The β-Ga2O3 epilayer that was N2 annealed for 15 min presented better photodetector performance than the as-grown β-Ga2O3 epilayer. The annealed epilayer exhibited a dark current of 1.6 × 10−13 A under 5 V bias.
A gas sensor based on a ZnGa 2 O 4 (ZGO) thin film grown by metalorganic chemical vapor deposition operated under the different temperature from 25 °C to 300 °C is investigated in this study. This sensor shows great sensing properties at 300 °C. The sensitivity of this sensor is 22.21 as exposed to 6.25 ppm of NO and its response time is 57 s. Besides that, the sensitivities are 1.18, 1.27, 1.06, and 1.00 when exposed to NO 2 (500 ppb), SO 2 (125 ppm), CO (125 ppm), and CO 2 (1500 ppm), respectively. These results imply that the ZGO gas sensor not only has high sensitivity, but also has great selectivity for NO gas. Moreover, the obtained results suggest that ZGO sensors are suitable for the internet of things(IOT) applications.
ZnGaO films were grown on c-plane sapphire substrates by metal organic chemical vapor deposition using diethylzinc (DEZn), triethylgallium (TEGa), and oxygen. The flow rate of DEZn was 10–60 sccm, and those of TEGa and oxygen were held constant. The ZnGaO film prepared at a DEZn flow rate of 10 sccm adopted a (2̅01)-oriented single-crystalline β-Ga2O3 phase, whereas those prepared at 30–60 sccm exhibited a (111)-oriented single-crystalline ZnGa2O4 phase. On the basis of Hall measurements, ZnGaO films (10 sccm DEZn) possessed very poor electrical properties, which were similar to those of β-Ga2O3. On the other hand, the carrier concentration in ZnGaO films increased from 1.94 × 1014 to 6.72 × 1016 cm–3, and the resistivity decreased from 5730 to 67.9 Ω-cm when increasing the DEZn flow rate from 30 to 60 sccm. According to compositional analyses, the improved electrical properties of ZnGaO films upon increasing DEZn flow rate from 30 to 40 sccm are due to the increasing Zn content, and the enhancement from 50 to 60 sccm could be due to increased C content. Cathodoluminescence results also confirm the ZnGa2O4 structure for ZnGaO films prepared at DEZn flow rates of 30–60 sccm and reveal their use for ultraviolet applications.
A single-crystalline ZnGa2O4 epilayer was successfully grown on c-plane (0001) sapphire substrate by metal-organic chemical vapor deposition. This epilayer was used as a ternary oxide semiconductor for application in high-performance metal–semiconductor–metal photoconductive deep-ultraviolet (DUV) photodetectors (PDs). At a bias of 5 V, the annealed ZnGa2O4 PDs showed better performance with a considerably low dark current of 1 pA, a responsivity of 86.3 A/W, cut-off wavelength of 280 nm, and a high DUV-to-visible discrimination ratio of approximately 107 upon exposure to 230 nm DUV illumination than that of as-grown ZnGa2O4 PDs. The as-grown PDs presented a dark current of 0.5 mA, a responsivity of 2782 A/W at 230 nm, and a photo-to-dark current contrast ratio of approximately one order. The rise time of annealed PDs was 0.5 s, and the relatively quick decay time was 0.7 s. The present results demonstrate that annealing process can reduce the oxygen vacancy defects and be potentially applied in ZnGa2O4 film-based DUV PD devices, which have been rarely reported in previous studies.
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