We demonstrate the facile, rational synthesis of monodispersedly sized zinc oxide (ZnO) nanowires from randomly sized seeds by hydrothermal growth. Uniformly shaped nanowire tips constructed in ammonia-dominated alkaline conditions serve as a foundation for the subsequent formation of the monodisperse nanowires. By precisely controlling the sharp tip formation and the nucleation, our method substantially narrows the distribution of ZnO nanowire diameters from σ = 13.5 nm down to σ = 1.3 nm and controls their diameter by a completely bottom-up method, even initiating from randomly sized seeds. The proposed concept of sharp tip based monodisperse nanowires growth can be applied to the growth of diverse metal oxide nanowires and thus paves the way for bottom-up grown metal oxide nanowires-integrated nanodevices with a reliable performance.

Single crystalline nanowires composed of semiconducting metal oxides formed via a vapor-liquid-solid (VLS) process exhibit an electrical conductivity even without an intentional carrier doping, although these stoichiometric metal oxides are ideally insulators. Suppressing this unintentional doping effect has been a challenging issue not only for metal oxide nanowires but also for various nanostructured metal oxides toward their semiconductor applications. Here we demonstrate that a pure VLS crystal growth, which occurs only at liquid-solid (LS) interface, substantially suppresses an unintentional doping of single crystalline SnO nanowires. By strictly tailoring the crystal growth interface of VLS process, we found the gigantic difference of electrical conduction (up to 7 orders of magnitude) between nanowires formed only at LS interface and those formed at both LS and vapor-solid (VS) interfaces. On the basis of investigations with spatially resolved single nanowire electrical measurements, plane-view electron energy-loss spectroscopy, and molecular dynamics simulations, we reveal the gigantic suppression of unintentional carrier doping only for the crystal grown at LS interface due to the higher annealing effect at LS interface compared with that grown at VS interface. These implications will be a foundation to design the semiconducting properties of various nanostructured metal oxides.

Relative humidity (RH) is an important physical quantity in industry, agriculture, and medical treatment. However, it is still challenging to exploit high-performance humidity sensors that can meet the detection requirement for responding to both high humidity variation and low humidity variation. In this work, ternary graphitic carbon nitride (g-C 3 N 4 ) nanosheet/TiO 2 nanoparticle/Ti 3 C 2 T x nanosheet composites were synthesized by in situ oxidation and thermal polymerization. The response of the g-C 3 N 4 /TiO 2 /Ti 3 C 2 T x sensor reaches 531 from 11−95% RH, which enhances 4, 11, and 450 times compared with that of TiO 2 , g-C 3 N 4 , and TiO 2 /Ti 3 C 2 T x sensors. Moreover, the ternary g-C 3 N 4 /TiO 2 /Ti 3 C 2 T x sensor demonstrates excellent reproducibility, fast response speed, low hysteresis loop, and good anti-interference ability. The as-fabricated g-C 3 N 4 /TiO 2 /Ti 3 C 2 T x sensor is further utilized in practical applications for human respiration detection and evaluation of waxing of fruits. The test results show that our fabricated sensor is capable of precisely sensing breathing status and distinguishing the waxing of fruits. In addition, our sensor can be used in most application scenarios and accelerate the integration of the Internet of Things (IoT).

Researchers have demonstrated great promise for inorganic nanowire use in analyzing cells or intracellular components. Although a stealth effect of nanowires toward cell surfaces allows preservation of the living intact cells when analyzing cells, as a completely opposite approach, the applicability to analyze intracellular components through disrupting cells is also central to understanding cellular information. However, the reported lysis strategy is insufficient for microbial cell lysis due to the cell robustness and wrong approach taken so far (i.e., nanowire penetration into a cell membrane). Here we propose a nanowire-mediated lysis method for microbial cells by introducing the rupture approach initiated by cell membrane stretching; in other words, the nanowires do not penetrate the membrane, but rather they break the membrane between the nanowires. Entangling cells with the bacteria-compatible and flexible nanowires and membrane stretching of the entangled cells, induced by the shear force, play important roles for the nanowire-mediated lysis to Gram-positive and Gram-negative bacteria and yeast cells. Additionally, the nanowire-mediated lysis is readily compatible with the loop-mediated isothermal amplification (LAMP) method because the lysis is triggered by simply introducing the microbial cells. We show that an integration of the nanowire-mediated lysis with LAMP provides a means for a simple, rapid, one-step identification assay (just introducing a premixed solution into a device), resulting in visual chromatic identification of microbial cells. This approach allows researchers to develop a microfluidic analytical platform not only for microbial cell identification including drug-and heat-resistance cells but also for on-site detection without any contamination.

We identify the effects of crystallinity and morphology of zinc oxide nanowires grown hydrothermally with ammonia addition on their physicochemical properties for capturing extracellular vesicles.

Ammonia is a well-known additive to promote crystal growth in hydrothermal synthesis of ZnO nanowires. Although the effect of ammonia on the nanowire growth has been intensively investigated, its influence on the seed layer, which governs the initial nanowire growth, is rarely discussed. Here, we demonstrate that ammonia strongly affects the seed layer as well as the following nanowire growth. On increasing the ammonia concentration, the nanowire density first increases and then decreases, while the nanowire growth rate keeps increasing. Experimental results and thermodynamic calculations of the initial growth process reveal that the transformation of the seed layer induced by ammonia prior to nucleation critically determines the nanowire density and thus also influences the following nanowire growth. Present results highlight the critical importance of discussing the variation of seed layers in ammonia-involved hydrothermal synthesis and suggest a novel seed engineering approach for tailoring the ZnO nanowire growth.

Since DNA analysis is the fundamental process for most applications in biomedical fields, capturing DNAs with high efficiency is important. Here, we used several oxide nanowire microfluidic devices to capture CpG-rich single-stranded DNAs (ssDNAs) in different pH solutions. All the oxide nanowires exhibited the highest capture efficiency around pH 7 with good capture efficiency shown by each metal oxide; ZnO/ZnO core/shell NWs (71.6%), ZnO/Al2O3 core/shell NWs (86.3%) and ZnO/SiO2 core/shell NWs (86.7%). ZnO/Al2O3 core/shell NWs showed the best performance for capturing ssDNAs under varying pH, which suggests its suitability for application in diverse biological fluids. The capturing efficiencies were attributed to the interactions from phosphate backbones and nucleobases of ssDNAs to each nanowire surface. This finding provides a useful platform for highly efficient capture of the target ssDNAs, and these results can be extended for future studies of cancer-related genes in complex biological fluids.

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