Erasable electrical conductive domain walls in an insulating ferroelectric matrix provide novel functionalities for applications in logic and memory devices. The crux of such success requires sufficiently high wall currents to drive high-speed and high-power nanodevices. This work provides an appealing strategy to increase the current by two orders of magnitude through the careful selection of current flowing paths along the charged walls. The dense walls come into form through the hierarchical evolution of the 71°, 109°, and 180° domains of epitaxial BiFeO 3 films in a planar-geometry ferroelectric resistance-switching memory cell. The engineered films grown on SrTiO 3 and GdScO 3 substrates allow the observation of detailed local configurations and the evolution of the different domain types using vector piezo-force microscopy. The higher local electrical conductivity near the charged domain walls is identified by conductive atomic-force microscopy. It is shown that 180° domain reversal proceeds by three-step 71° rotations of the pristine domains. Surprisingly, a maximum current of ≈300 nA is observed for current paths along charge-uncompensated head-to-head hierarchical domain walls connecting the two electrodes on the film surface. Furthermore, the achievable current level can be conveniently controlled by varying the relative directions of the initial polarization and the applied field.
Composite nanoparticles have proved to be promising in a wide range of biotechnological applications. In this paper, we report on a facile method to synthesize novel Fe(3)O(4)/Au/Fe(3)O(4) nanoparticles (nanoflowers) that integrate hybrid components and surface types. We demonstrate that relative to conventional nanoparticles with core/shell configuration, such nanoflowers not only retain their surface plasmon property but also allow for 170% increase in the saturation magnetization and 23% increase in the conjugation efficiency due to the synergistic co-operation between the hierarchical structures. Moreover, we demonstrate that the magnetic properties of such composite nanoparticles can be tuned by controlling the size of additional petals (Fe(3)O(4) phase). These novel building blocks could open up novel and exciting vistas in nanomedicine for broad applications such as biosensing, cancer diagnostics and therapeutics, targeted delivery, and imaging.
One-dimensional mesoporous TiO2-Bi2WO6 hollow superstructures are prepared using a hydrothermal method and their photocatalysis and recycle properties are investigated. Experimental results indicate that anatase TiO2 nanoparticles are coupled with hierarchical Bi2WO6 hollow tubes on their surfaces. The TiO2-Bi2WO6 structure has a mesoporous wall and the pores in the wall are on average 21 nm. The hierarchical TiO2-Bi2WO6 heterostructures exhibit the highest photocatalytic activity in comparison with P25, pure Bi2WO6 hollow tube and mechanical mixture of Bi2WO6 tube and TiO2 nanoparticle in the degradation of rhodamine B (RhB) under simulated sunlight irradiation. The as-prepared TiO2-Bi2WO6 heterostructures can be easily recycled through sedimentation and they retains their high photocatalytic activity during the cycling use in the simulated sunlight-driving photodegradation process of RhB. The prepared mesoporous TiO2-Bi2WO6 with hollow superstructure is therefore a promising candidate material for water decontamination use.
Structure-switching aptamers (SSAs) offer a promising recognition element for sensor development. However, the generation of SSAs via in vitro aptamer selection technologies or postselection engineering is challenging. Inspired by the two-domain structure of antibodies, we have devised a simple, universal strategy for engineering aptamers into SSAs with signal reporting functionality. These constructs consist of a “constant” domain, comprising a split DNAzyme G-quadruplex (G4) region for signal transduction, and a “variable” domain, comprising an aptamer sequence capable of specific target binding. In the absence of target, the G4-SSA construct folds into a parallel G4 structure with high peroxidase catalytic activity. Target binding disrupts the G4 structure, resulting in low enzymatic activity. We demonstrate that this change in DNAzyme activity enables sensitive and specific colorimetric detection of diverse targets including Hg2+, thrombin, sulfadimethoxine, cocaine, and 17β-estradiol. G4-SSAs can also achieve label-free fluorescence detection of various targets using a specific G4-binding dye. We demonstrate that diverse aptamers can be readily engineered into G4-SSA constructs independent of target class, binding affinity, aptamer length, or structure. This design strategy could broadly extend the power, accessibility, and utility of numerous SSA-based biosensors.
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