MicroRNAs (miRNAs) play vital roles in physiologic and pathologic processes and are significant biomarkers for disease diagnostics and therapeutics. However, rapid, low-cost, sensitive, and selective detection of miRNAs remains a challenge because of their short length, sequence homology, and low abundance. Herein, we report for the first time that WS2 nanosheet can exhibit differential affinity toward short oligonucleotide fragment versus ssDNA probe and act as an efficient quencher for adsorbed fluorescent probes. This finding is utilized to develop a new strategy for simple, sensitive, and selective detection of miRNA by combining WS2 nanosheet based fluorescence quenching with duplex-specific nuclease signal amplification (DSNSA). This assay exhibits highly sensitive and selective with a detection limit of 300 fM and even discriminate single-base difference between the miRNA family members. The result indicates that this simple and cost-effective strategy holds great potential application in biomedical research and clinical diagnostics.
Compression of hydrogen-rich hydrides has been proposed as an alternative way to attain the atomic metallic hydrogen state or high-temperature superconductors. However, it remains a challenge to get access to these states by synthesizing novel polyhydrides with unusually high hydrogen-to-metal ratios. Here we synthesize a series of cerium (Ce) polyhydrides by a direct reaction of Ce and H 2 at high pressures. We discover that cerium polyhydride CeH 9 , formed above 100 GPa, presents a three-dimensional hydrogen network composed of clathrate H 29 cages. The electron localization function together with band structure calculations elucidate the weak electron localization between H-H atoms and confirm its metallic character. By means of Ce atom doping, metallic hydrogen structure can be realized via the existence of CeH 9 . Particularly, Ce atoms play a positive role to stabilize the sublattice of hydrogen cages similar to the recently discovered near-room-temperature lanthanum hydride superconductors.
Superhydrides have complex hydrogenic sublattices and are important prototypes for studying metallic hydrogen and high-temperature superconductors. Encouraged by the results on LaH10, in consideration of the differences between La and Pr, Pr-H system is especially worth studying because of the magnetism and valence-band f-electrons in element Pr. Here we successfully synthesized praseodymium superhydrides (PrH9) in laser-heated diamond anvil cells. Synchrotron X-ray diffraction (XRD) analysis demonstrated the presence of previously predicted F4 ̅ 3m-PrH9 and unexpected P63/mmc-PrH9 phases. Moreover, Fm3 ̅ m-PrH3, P4/nmm-PrH3-δ and Fm3 ̅ m-PrH1+x were found below 52 GPa. F4 ̅ 3m-PrH9 and P63/mmc-PrH9 were stable above 100 GPa in experiment. Experimental studies of electrical resistance in the PrH9 sample showed the emergence of superconducting transition (Tc) below 9 K and a dependent Tc on applied magnetic field. Theoretical calculations indicate that magnetic order and electron-phonon interaction coexist in a very close range of pressures in the PrH9 sample which may contribute to its low superconducting temperature Tc. Our results highlight the intimate connections among hydrogenic sublattices, density of states, magnetism and superconductivity in Pr-based superhydrides.
Fluorescent signal-based lateral flow immunochromatographic strips (FLFICS) have received great expectations since they combine the quantitative sensitivity of fluorescence analysis and the simplicity, rapidness, and portability of a common lateral flow immunochromatographic strip (LFICS).
Emergent Dirac fermion states underlie many intriguing properties of graphene, and the search for them constitute one strong motivation to explore two-dimensional (2D) allotropes of other elements. Phosphorene, the ultrathin layers of black phosphorous, has been a subject of intense investigations recently, and it was found that other group-Va elements could also form 2D layers with similar puckered lattice structure. Here, by a close examination of their electronic band structure evolution, we discover two types of Dirac fermion states emerging in the low-energy spectrum. One pair of (type-I) Dirac points is sitting on high-symmetry lines, while two pairs of (type-II) Dirac points are located at generic k-points, with different anisotropic dispersions determined by the reduced symmetries at their locations. Such fullyunpinned (type-II) 2D Dirac points are discovered for the first time. In the absence of spinorbit coupling, we find that each Dirac node is protected by the sublattice symmetry from gap opening, which is in turn ensured by any one of three point group symmetries. The spinorbit coupling generally gaps the Dirac nodes, and for the type-I case, this drives the system into a quantum spin Hall insulator phase. We suggest possible ways to realize the unpinned Dirac points in strained phosphorene.
Search for room-temperature superconductivity is inspired by the unique properties of the electron-phonon interaction in metal superhydrides. Encouraged by the recently found highest-TC superconductor fcc-LaH10, here we discover several polyhydrides of another lanthanideneodymium. We identified three novel metallic Nd-H phases at pressures of 90 to 130 GPa: I4/mmm-NdH4, C2/с-NdH7, and P63/mmc-NdH9+x (x = 0-0.5), synthesized by laser-heating metal samples in NH3BH3 media for in situ generation of hydrogen. A lower trihydride Fm3 ̅ m-NdH3 was found at pressures from 2 to 52 GPa. I4/mmm-NdH4 and C2/с-NdH7 were stable from 130 down to 85 GPa, and P63/mmc-NdH9+x -at 110 to 130 GPa. Theoretical calculations predict that all the neodymium hydrides have a strong magnetism at pressures below 150 GPa (> 2.2 μB per Nd atom): C2/c-NdH7 and hcp-NdH9 possess collinear anti-ferromagnetic [110] and [100]2 orders respectively, while NdH4 is a ferromagnetic with the (110) easy-axis. The critical Curie or Neel temperatures for new neodymium hydrides were estimated using the mean-field approximation as 100 K (NdH7), 95 K (NdH9) and 167 K (NdH4).
A reversible addition–fragmentation chain transfer (RAFT) agent, 2‐cyanoprop‐2‐yl 1‐dithionaphthalate (CPDN), was synthesized and applied to the RAFT polymerization of glycidyl methacrylate (GMA). The polymerization was conducted both in bulk and in a solvent with 2,2′‐azobisisobutyronitrile (AIBN) as the initiator at various temperatures. The results for both types of polymerizations showed that GMA could be polymerized in a controlled way by RAFT polymerization with CPDN as a RAFT agent; the polymerization rate was first‐order with respect to the monomer concentration, and the molecular weight increased linearly with the monomer conversion up to 96.7% at 60 °C, up to 98.9% at 80 °C in bulk, and up to 64.3% at 60 °C in a benzene solution. The polymerization rate of GMA in bulk was obviously faster than that in a benzene solution. The molecular weights obtained from gel permeation chromatography were close to the theoretical values, and the polydispersities of the polymer were relatively low up to high conversions in all cases. It was confirmed by a chain‐extension reaction that the AIBN‐initiated polymerizations of GMA with CPDN as a RAFT agent were well controlled and were consistent with the RAFT mechanism. The epoxy group remained intact in the polymers after the RAFT polymerization of GMA, as indicated by the 1H NMR spectrum. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2558–2565, 2004
We conducted a joint experimental−theoretical investigation of the high-pressure chemistry of europium polyhydrides at pressures of 86−130 GPa. We discovered several novel magnetic Eu superhydrides stabilized by anharmonic effects: cubic EuH 9 , hexagonal EuH 9 , and an unexpected cubic (Pm3n) clathrate phase, Eu 8 H 46 . Monte Carlo simulations indicate that cubic EuH 9 has antiferromagnetic ordering with T N of up to 24 K, whereas hexagonal EuH 9 and Pm3n-Eu 8 H 46 possess ferromagnetic ordering with T C = 137 and 336 K, respectively. The electron−phonon interaction is weak in all studied europium hydrides, and their magnetic ordering excludes s-wave superconductivity, except, perhaps, for distorted pseudohexagonal EuH 9 . The equations of state predicted within the DFT+U approach (U − J were found within linear response theory) are in close agreement with the experimental data. This work shows the great influence of the atomic radius on symmetry-breaking distortions of the crystal structures of superhydrides and on their thermodynamic stability.
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