171 research outputs found
Supporting Information for: A highly efficient form of the selenocysteine insertion sequence element in protozoan parasites and its use in mammalian cells
Selenoproteins are an elite group of proteins containing a rare amino acid, selenocysteine (Sec), encoded by the codon, UGA. In eukaryotes, incorporation of Sec requires a Sec insertion sequence (SECIS) element, a stem–loop structure located in the 3\u27-untranslated regions of selenoprotein mRNAs. Here we report identification of a noncanonical form of SECIS element in Toxoplasma gondii and Neospora canine, single-celled apicomplexan parasites of humans and domestic animals. This SECIS has a GGGA sequence in the SBP2-binding site in place of AUGA previously considered invariant. Using a combination of computational and molecular techniques, we show that Toxoplasma and Neospora possess both canonical and noncanonical SECIS elements. The GGGA-type SECIS element supported Sec insertion in mammalian HEK 293 and NIH 3T3 cells and did so more efficiently than the natural mammalian SECIS elements tested. In addition, mammalian type I and type II SECIS elements mutated into the GGGA forms were functional but manifested decreased Sec insertion efficiency. We carried out computational searches for both AUGA and GGGA forms of SECIS elements in Toxoplasma and detected five selenoprotein genes, including one coding for a previously undescribed selenoprotein, designated SelQ, and two containing the GGGA form of the SECIS element. In contrast, the GGGA-type SECIS elements were not detected in mammals and nematodes. As a practical outcome of the study, we developed pSelExpress1, a vector for convenient expression of selenoproteins in mammalian cells. It contains an SBP2 gene and the most efficient tested SECIS element: an AUGA mutant of the GGGA-type Toxoplasma SelT structure
High-Yield Production and Transfer of Graphene Flakes Obtained by Anodic Bonding
We report large-yield production of graphene flakes on glass by anodic
bonding. Under optimum conditions, we counted several tens of flakes with
lateral size around 20-30 {\mu}m and few tens of flakes with larger size.
60-70% of the flakes have negligible D peak. We show that it is possible to
easily transfer the flakes by wedging technique. The transfer on silicon does
not damage graphene and lowers the doping. The charge mobility of the
transferred flakes on silicon is of the order of 6000 cm^2/V s (at carrier
concentration of 10^12 cm^-2), which is typical for devices prepared on this
substrate with exfoliated graphene.Comment: 17 pages, 6 figures; ACS Nano 201
Specific Excision of the Selenocysteine tRNA\u3csup\u3e [Ser]Sec\u3c/sup\u3e (\u3ci\u3eTrsp\u3c/i\u3e) Gene in Mouse Liver Demonstrates an Essential Role of Selenoproteins in Liver Function
Selenium is essential in mammalian embryonic development. However, in adults, selenoprotein levels in several organs including liver can be substantially reduced by selenium deficiency without any apparent change in phenotype. To address the role of selenoproteins in liver function, mice homozygous for a floxed allele encoding the selenocysteine (Sec) tRNA [Ser]Sec gene were crossed with transgenic mice carrying the Cre recombinase under the control of the albumin promoter that expresses the recombinase specifically in liver. Recombination was nearly complete in mice 3 weeks of age, whereas liver selenoprotein synthesis was virtually absent, which correlated with the loss of Sec tRNA [Ser]Sec and activities of major selenoproteins. Total liver selenium was dramatically decreased, whereas levels of low molecular weight selenocompounds were little affected. Plasma selenoprotein P levels were reduced by about 75%, suggesting that selenoprotein P is primarily exported from the liver. Glutathione S-transferase levels were elevated in the selenoprotein-deficient liver, suggesting a compensatory activation of this detoxification program. Mice appeared normal until about 24 h before death. Most animals died between 1 and 3 months of age. Death appeared to be due to severe hepatocellular degeneration and necrosis with concomitant necrosis of peritoneal and retroperitoneal fat. These studies revealed an essential role of selenoproteins in liver function
Atomically thin boron nitride: a tunnelling barrier for graphene devices
We investigate the electronic properties of heterostructures based on
ultrathin hexagonal boron nitride (h-BN) crystalline layers sandwiched between
two layers of graphene as well as other conducting materials (graphite, gold).
The tunnel conductance depends exponentially on the number of h-BN atomic
layers, down to a monolayer thickness. Exponential behaviour of I-V
characteristics for graphene/BN/graphene and graphite/BN/graphite devices is
determined mainly by the changes in the density of states with bias voltage in
the electrodes. Conductive atomic force microscopy scans across h-BN terraces
of different thickness reveal a high level of uniformity in the tunnel current.
Our results demonstrate that atomically thin h-BN acts as a defect-free
dielectric with a high breakdown field; it offers great potential for
applications in tunnel devices and in field-effect transistors with a high
carrier density in the conducting channel.Comment: 7 pages, 5 figure
Application of Thin Piezoelectric Films in Diamond-Based Acoustoelectronic Devices
The theory of external loading influence on acoustic parameters of piezoelectric five-layered structure as “Al/(001) AlN/Mo/(001) diamond/Me” has been developed. Oscillations in diamond-based high-overtone bulk acoustic resonators (HBARs) have been investigated in terms of 3D FEM simulation. Peculiarities of technology of aluminum-scandium nitride (ASN) films have been discussed. Composition Al0.8Sc0.2N was obtained to create the diamond-based HBAR and SAW resonator. Application of ASN films has resulted in a drastic increasing an electromechanical coupling up to 2.5 times in comparison with aluminum nitride. Development of ASN technology in a way of producing a number of compositions with the better piezoelectric properties has a clear prospective. SAW resonator based on “Al IDT/(001) AlN/(001) diamond” structure has been investigated in the band 400–1500 MHz. The highest-quality factor Q ≈ 1050 was observed for the Sezawa mode at 1412 MHz. Method of measuring HBAR’s parameters within 4–400 K at 0.5–5 GHz has been developed. Results on temperature dependence of diamond’s Q-factor at relatively low frequencies were quite different in comparison with the ones at the frequencies up to 5 GHz. Difference could be explained in terms of changing mechanism of acoustic attenuation from Akhiezer’s type to the Landau-Rumer’s one at higher frequencies in diamond
Vertical Field Effect Transistor based on Graphene-WS2 Heterostructures for flexible and transparent electronics
The celebrated electronic properties of graphene have opened way for
materials just one-atom-thick to be used in the post-silicon electronic era. An
important milestone was the creation of heterostructures based on graphene and
other two-dimensional (2D) crystals, which can be assembled in 3D stacks with
atomic layer precision. These layered structures have already led to a range of
fascinating physical phenomena, and also have been used in demonstrating a
prototype field effect tunnelling transistor - a candidate for post-CMOS
technology. The range of possible materials which could be incorporated into
such stacks is very large. Indeed, there are many other materials where layers
are linked by weak van der Waals forces, which can be exfoliated and combined
together to create novel highly-tailored heterostructures. Here we describe a
new generation of field effect vertical tunnelling transistors where 2D
tungsten disulphide serves as an atomically thin barrier between two layers of
either mechanically exfoliated or CVD-grown graphene. Our devices have
unprecedented current modulation exceeding one million at room temperature and
can also operate on transparent and flexible substrates
Transition metal dichalcogenide nanospheres for high-refractive-index nanophotonics and biomedical theranostics
Recent developments in the area of resonant dielectric nanostructures have created attractive opportunities for concentrating and manipulating light at the nanoscale and the establishment of the new exciting field of all-dielectric nanophotonics. Transition metal dichalcogenides (TMDCs) with nanopatterned surfaces are especially promising for these tasks. Still, the fabrication of these structures requires sophisticated lithographic processes, drastically complicating application prospects. To bridge this gap and broaden the application scope of TMDC nanomaterials, we report here femtosecond laser-ablative fabrication of water-dispersed spherical TMDC (MoS2 and WS2) nanoparticles (NPs) of variable size (5 to 250 nm). Such NPs demonstrate exciting optical and electronic properties inherited from TMDC crystals, due to preserved crystalline structure, which offers a unique combination of pronounced excitonic response and high refractive index value, making possible a strong concentration of electromagnetic field in the NPs. Furthermore, such NPs offer additional tunability due to hybridization between the Mie and excitonic resonances. Such properties bring to life a number of nontrivial effects, including enhanced photoabsorption and photothermal conversion. As an illustration, we demonstrate that the NPs exhibit a very strong photothermal response, much exceeding that of conventional dielectric nanoresonators based on Si. Being in a mobile colloidal state and exhibiting superior optical properties compared to other dielectric resonant structures, the synthesized TMDC NPs offer opportunities for the development of next-generation nanophotonic and nanotheranostic platforms, including photothermal therapy and multimodal bioimaging
Chiral photonic super-crystals based on helical van der Waals homostructures
Chirality is probably the most mysterious among all symmetry transformations.
Very readily broken in biological systems, it is practically absent in
naturally occurring inorganic materials and is very challenging to create
artificially. Chiral optical wavefronts are often used for the identification,
control and discrimination of left- and right-handed biological and other
molecules. Thus, it is crucially important to create materials capable of
chiral interaction with light, which would allow one to assign arbitrary chiral
properties to a light field. In this paper, we utilized van der Waals
technology to assemble helical homostructures with chiral properties (e. g.
circular dichroism). Because of the large range of van der Waals materials
available such helical homostructures can be assigned with very flexible
optical properties. We demonstrate our approach by creating helical
homostructures based on multilayer AsS, which offers the most
pronounced chiral properties even in thin structures due to its strong biaxial
optically anisotropy. Our work showcases that the chirality of an
electromagnetic system may emerge at an intermediate level between the
molecular and the mesoscopic one due to the tailored arrangement of non-chiral
layers of van der Waals crystals and without additional patterning
How close can one approach the Dirac point in graphene experimentally?
The above question is frequently asked by theorists who are interested in
graphene as a model system, especially in context of relativistic quantum
physics. We offer an experimental answer by describing electron transport in
suspended devices with carrier mobilities of several 10^6 cm^2V^-1s^-1 and with
the onset of Landau quantization occurring in fields below 5 mT. The observed
charge inhomogeneity is as low as \approx10^8 cm^-2, allowing a neutral state
with a few charge carriers per entire micron-scale device. Above liquid helium
temperatures, the electronic properties of such devices are intrinsic, being
governed by thermal excitations only. This yields that the Dirac point can be
approached within 1 meV, a limit currently set by the remaining charge
inhomogeneity. No sign of an insulating state is observed down to 1 K, which
establishes the upper limit on a possible bandgap
Exploring van der Waals materials with high anisotropy: geometrical and optical approaches
The emergence of van der Waals (vdW) materials resulted in the discovery of
their giant optical, mechanical, and electronic anisotropic properties,
immediately enabling countless novel phenomena and applications. Such success
inspired an intensive search for the highest possible anisotropic properties
among vdW materials. Furthermore, the identification of the most promising
among the huge family of vdW materials is a challenging quest requiring
innovative approaches. Here, we suggest an easy-to-use method for such a survey
based on the crystallographic geometrical perspective of vdW materials followed
by their optical characterization. Using our approach, we found As2S3 as a
highly anisotropic vdW material. It demonstrates rare giant in-plane optical
anisotropy, high refractive index and transparency in the visible range,
overcoming the century-long record set by rutile. Given these benefits, As2S3
opens a pathway towards next-generation nanophotonics as demonstrated by an
ultrathin true zero-order quarter-waveplate that combines classical and the
Fabry-Perot optical phase accumulations. Hence, our approach provides an
effective and easy-to-use method to find vdW materials with the utmost
anisotropic properties.Comment: 11 pages, 5 figure
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