[en] Highlights: • A DNA sensor based on hybridization chain reaction and G-quadruplex-hemin complex. • High sensitive detection of HIV DNA was achieved with the detection limit down to fM level. • The DNA sensor can discriminate mismatched sequences of HIV DNA sequence. • The DNA sensor was applied in detection of the target DNA in serum. - Abstract: A high-sensitive detection of sequence-specific DNA was established based on the formation of G-quadruplex-hemin complex through continuous hybridization chain reaction (HCR). Taking HIV DNA sequence as an example, a capture probe complementary to part of HIV DNA was firstly self-assembled onto the surface of Au electrode. Then a specially designed assistant probe with both terminals complementary to the target DNA and a G-quadruplex-forming sequence in the center was introduced into the detection solution. In the presence of both the target DNA and the assistant probe, the target DNA can be captured on the electrode surface and then a continuous HCR can be conducted due to the mutual recognition of the target DNA and the assistant probe, leading to the formation of a large number of G-quadruplex on the electrode surface. With the help of hemin, a pronounced electrochemical signal can be observed in differential pulse voltammetry (DPV), due to the formation of G-quadruplex-hemin complex. The peak current is linearly related with the logarithm of the concentration of the target DNA in the range from 10 fM to 10 pM. The electrochemical sensor has high selectivity to clearly discriminate single-base mismatched and three-base mismatched sequences from the original HIV DNA sequence. Moreover, the established DNA sensor was challenged by detection of HIV DNA in human serum samples, which showed the low detection limit of 6.3 fM. Thus it has great application prospect in the field of clinical diagnosis and environmental monitoring.

[en] Motivated by the experimental realization of D0₂₂-type Mn₃Ge (001) films [Kurt et al. Appl. Phys. Lett. 101, 132410 (2012)] and the structural stability of D0₃-type Heusler alloy Mn₃Ge [Zhang et al. J. Phys.: Condens. Matter 25, 206006 (2013)], we use the first-principles calculations based on the full potential linearized augmented plane-wave method to investigate the electronic and magnetic properties of D0₃-type Heusler alloy Mn₃Ge and its (001) surface. We show that bulk D0₃-Mn₃Ge is a half-metallic ferromagnet with the minority-spin energy gap of 0.52 eV and the magnetic moment of 1.00 μ_B per formula unit. The bulk half-metallicity is preserved at the pure Mn-terminated (001) surface due to the large exchange split, but the MnGe-terminated (001) surface destroys the bulk half-metallicity. We also reveal that the surface stabilities are comparable between the D0₃-Mn₃Ge (001) and the experimental D0₂₂-Mn₃Ge (001), which indicates the feasibility to grow the Mn₃Ge (001) films with D0₃ phase other than D0₂₂ one. The surface half-metallicity and stability make D0₃-Mn₃Ge a promising candidate for spintronic applications

[en] Core/shell Fe_3O_4/BiOI nanoparticles with BiOI sheath have been synthesized by a solvothermal reaction method and were characterized by transmission electron microscopy (TEM) with an energy dispersive spectrum (EDS), high-resolution TEM and X-ray diffraction (XRD). Their photocatalytic activities were evaluated by methylene blue (MB) under the simulated solar light. The results indicate that the spherical Fe_3O_4 particles were coated with BiOI sheath when the sample were synthesized at 160 °C with ethylene glycol and deionized water, forming a core/shell structure. The degradation rate of MB assisted with the core/shell Fe_3O_4/BiOI catalysts reached 98 % after 40-min irradiation. The catalytic performance enhancement of the core/shell Fe_3O_4/BiOI catalysts mainly attributes to the band structure that can improve the generation efficiency, separation and transfer process of the photo-induced electron–hole pairs and decrease their recombination. The magnetic Fe_3O_4 core not only contributes to the efficient separation of electron and holes, but also helps catalysts be collected conveniently using a magnet for reuse. After five repeated trials, the degradation rate of MB still maintains over 90 % and the saturated magnetization of the catalysts remains 51.5 emu/g, which indicate that the core/shell Fe_3O_4/BiOI nanoparticles have excellent photocatalytic stability and are recyclable for decomposing organic pollutants under visible light irradiation.

[en] Thin polymer films with patterned surfaces have drawn tremendous attention in manufacturing advanced electronic, mechanical devices and in biomaterials due to the advantageous properties such as mechanical strength, chemical resistance and optic transparency. The applications can be extended to the fields such as catalysts, antireflection coatings, template for inorganic growth masks, and substrates for cell culturing providing the patterned surface containing micron-sized features. Various methods have been used to fabricate polymers with micro-patterned surfaces such as photolithographic, ink-jet printing, nonsolvent, spin coating in a dry environment, self-organization, and the condensation of monodisperse water droplet on the polymer solution. The physiological functions of mature cells depend on the microenvironment/niche surrounding which can provide proper factors to regulate cell proliferation and differentiation. While designing appropriate scaffolds for tissue engineering, the microstructure is one of the most important factors to be considered. In this work, a facile single-step phase separation method was used to create micro-patterned polymer thin films with concaves or convexes with sizes ranged from 7 to 70 μm. The effects of water content, casting volume and the addition of surfactant on the distribution of pores and substrate morphology were examined. Moreover, detailed observations of fibroblast cells on the micro-patterned thin films were presented to compare and elucidate the roles of surface micro-features and chemical functionalities.

[en] We report ab initio calculations of electronic transport properties of heterostructure based on MoS₂ nanoribbons. The heterostructure consists of edge hydrogen-passivated and non-passivated zigzag MoS₂ nanoribbons (ZMoS₂NR-H/ZMoS₂NR). Our calculations show that the heterostructure has half-metallic behavior which is independent of the nanoribbon width. The opening of spin channels of the heterostructure depends on the matching of particular electronic orbitals in the Mo-dominated edges of ZMoS₂NR-H and ZMoS₂NR. Perfect spin filter effect appears at small bias voltages, and large negative differential resistance and rectifying effects are also observed in the heterostructure.

[en] Highlights: • A quantum mechanical model determined cations substituted problem. • Only nine kinds of cations can be all substituted into Pb sites. • The first principle identified the nine kinds of structural stability. • Nine kinds of cations substituted can control the band gap. -- Abstract: Organic-inorganic hybrid CH₃NH₃PbI₃ perovskite has a great potential for applications in low-cost photovoltaic devices. However, the doped and substitution of Pb sites in CH₃NH₃PbI₃ has not been widely reported. In this article, a quantum mechanical model was applied to determine why all divalent cations cannot substitute the Pb cations of CH₃NH₃PbI₃ perovskite. The evaluation was performed by comparison the model with experimental results. On this basis, we carefully examined 42 types of cations and identified only nine kinds of cations including Ca²⁺, Sr²⁺, Sc²⁺, Ti²⁺, V²⁺, Y²⁺, Zr²⁺, Nb²⁺ and Sn²⁺ for doped into Pb sites. In these cases, it is expected that the corresponding compound would be single phase. Finally, an analysis was performed based on first principle, and the results indicate that divalent cations substituting the Pb sites modify the band structure and influence the performance of perovskite-based photostatics.

[en] Magnetic properties of spin-1/2 antiferromagnetic three-leg Heisenberg ladders, where antiferromagnetic interactions in legs are J_1, J_2 and J_1 respectively and in the rungs are J_⊥, have been investigated by bond-mean field method. As J_⊥ changes, magnetization curves show different behavior. For J_⊥=0.5, there are cusps in magnetization curves, while for J_⊥=3.0, the 1/3 magnetization plateau appears, which can be explained by energy spectra. Furthermore, for J_⊥=3.0 the 1/3 magnetization plateaus will become wider or narrow down with J_2 changing. In addition, the mean-field bond parameters and the concurrences, which confirm the phase transitions, are also studied. - Highlights: • The spectral functions for different magnetic interactions are investigated. • The 1/3 magnetization plateaus will become wider or narrow down with J_2 changing. • The mean-field bond parameters and concurrences characterize phase transitions.

[en] Based on the experimental synthesis of organic compound verdazyl radical β-3-(2,6-dichlorophenyl)-1,5-diphenylverdazyl, consisting of four antiferromagnetic couplings, we study the magnetic properties and thermodynamic behaviors for different antiferromagnetic interactions using Green’s function theory. Under different fields, there are five regimes containing two gapless phases and three magnetization plateaus (M=0, 1/2 and saturated magnetization) distinguished by four critical lines, which are evidenced by the two-site entanglement entropy and closely related to the energy spectra. In addition, we calculate the susceptibility and specific heat, to demonstrate the low-lying excitations at low temperatures. It will provide guidance for us to synthesize varieties of unconventional magnetic materials, and stimulate future studies on quantum spin systems. - Highlights: • The antiferromagnetic interaction-magnetic field phase diagrams are constructed. • The magnetization per site makes different contribution to the 1/2 plateau. • The spectral functions for different magnetic interactions are studied. • We investigate the gapless or gapped low-lying excitations at low temperatures