Plasmon-Induced Trap State Emission from Single Quantum Dots.

Charge carriers trapped at localized surface defects play a crucial role in quantum dot (QD) photophysics. Surface traps offer longer lifetimes than band-edge emission, expanding the potential of QDs as nanoscale light-emitting excitons and qubits. Here, we demonstrate that a nonradiative plasmon mode drives the transfer from two-photon-excited excitons to trap states. In plasmonic cavities, trap emission dominates while the band-edge recombination is completely suppressed. The induced pathways for excitonic recombination not only shed light on the fundamental interactions of excitonic spins, but also open new avenues in manipulating QD emission, for optoelectronics and nanophotonics applications.

Theoretical estimation of size effects on the electronic transport in tailored graphene nanoribbons.

Focusing on the potential applications of tailored graphene nanoribbons (t-GNRs), in this work, we systematically study size effects on the electronic transport in t-GNR-based molecular junctions. As a result of the manufacturing error generated during the processing or synthesis of t-GNRs using techniques such as ion beam lithography, the final dimensions of the as-fabricated devices often deviate from the design values, giving rise to a size distribution around the mean value which could considerably affect the device performance. To simulate the effects of the manufacturing error, a series of t-GNR-based junctions with various dimensions have been modelled and systematically investigated using density functional theory (DFT) coupled with the non-equilibrium Green's function (NEGF). For junctions that consist of an acene chain connected with two graphene nanosheets, it is found that the chain length has little influence on the electronic transport and that, on the other hand, the junction conductivity is significantly altered by its width due to the different number and nature of the electron transfer pathways. Furthermore, increasing the width of the junction leads to a clear odd-even variation of decreasing amplitude in its transport behavior. These findings underpin further fundamental and device-based studies of t-GNRs.

High-Fidelity Determination and Tracing of Small Extracellular Vesicle Cargoes.

Direct tracing of small extracellular vesicle (sEV) cargoes holds unprecedented importance for elucidating the mechanisms involved in intercellular communication. However, high-fidelity determination of sEVs' molecular cargoes in situ has yet to be achieved due to the difficulty in transporting molecular probes into intact sEVs. Herein, a fLuorescent Intracellular-Guided Hairpin-Tetrahedron (fLIGHT) nanoprobe is described for direct visualization of sEV microRNAs in situ. Integrating the advantages of nondestructive sEV penetration via DNA origami and single-nucleotide discrimination as well as wash-free fluorescence readout using a hairpin probe, the proposed approach enables high-fidelity fluorescence visualization of sEVs' microRNA without RNA extraction or leakage, demonstrating the potential of on-site tracing of sEV cargoes. This strategy opens an avenue to establishing universal molecular detection and labeling platforms that can facilitate both sEV-derived fundamental biological studies and molecular diagnostics.

SRGN, a new identified shear-stress-responsive gene in endothelial cells.

Endothelial cells (ECs) play an important role in the pathogenesis of cardiovascular disease, especially atherosclerosis (AS). The abnormal wall shear stress (WSS) which directly contacts with ECs is the key stimulating factor leading to AS. However, the underlying mechanism of ECs responding to WSS is still incompletely understood. This study aims to explore the novel mechano-sensitive genes and its potential mechanism in response to WSS in ECs by employing bioinformatics methods based on previously available high-throughput data from zebrafish embryos, both before and after blood flow formation. Six common differentially expressed genes (DEGs) (SRGN, SLC12A3, SLC25A4, PVALB1, ITGAE.2, zgc:198419) were selected out from two high-throughput datasets (GSE126617 and GSE20707) in the GEO database. Among them, SRGN was chosen for further verification through the in vitro shear stress loading experiments with human umbilical vein endothelial cells (HUVECs) and the in vivo partial ligation of carotid artery in mice. Our data indicated that low shear stress (LSS) could enhance the expression of SRGN via the PKA/CREB-dependent signaling pathway. The proportion of Ki67+ cells and the concentration of nitric oxide (NO) were high in SRGN high expression cells, suggesting that SRGN may be involved in the proliferation of HUVECs. Furthermore, in the partial ligation of the carotid artery mice model, we observed that the expression of SRGN was significantly increased in atherosclerotic plaques induced by abnormal shear stress. Taken together, this study demonstrated that SRGN is a key gene in the response of ECs to WSS and could be involved in AS.

Anomalously Large Spectral Shifts near the Quantum Tunnelling Limit in Plasmonic Rulers with Subatomic Resolution.

The resonance wavelength of a coupled plasmonic system is extremely sensitive to the distance between its metallic surfaces, resulting in "plasmon rulers". We explore this behavior in the subnanometer regime using self-assembled monolayers of bis-phthalocyanine molecules in a nanoparticle-on-mirror (NPoM) construct. These allow unprecedented subangstrom control over spacer thickness via choice of metal center, in a gap-size regime at the quantum-mechanical limit of plasmonic enhancement. A dramatic shift in the coupled plasmon resonance is observed as the gap size is varied from 0.39 to 0.41 nm. Existing theoretical models are unable to account for the observed spectral tuning, which requires inclusion of the quantum-classical interface, emphasizing the need for new treatments of light at the subnanoscale.

Adsorption of 4-n-Nonylphenol, Carvacrol, and Ethanol onto Iron Oxide from Nonaqueous Hydrocarbon Solvents.

The adsorption of 4-n-nonylphenol (4NP), carvacrol, and ethanol onto the surface of iron oxide from nonaqueous solutions is presented. It is found that adsorption of 4NP from alkanes is strong and proceeds to monolayer formation, where the molecules are essentially "upright". However, at high relative concentrations, ethanol successfully out-competes 4NP for the iron oxide surface. Estimates of the enthalpy and entropy of binding of 4NP were found to be exothermic and entropically disfavored. Sum frequency generation vibrational spectroscopy data indicate some evidence of binding through a phenolate anion, despite the nonpolar, nonaqueous solvent. Carvacrol is also found to adsorb as a monolayer where the molecules are lying "flat". The adsorption of ethanol onto iron oxide from dodecane was investigated through the use of quantitative NMR, which is a convenient analytical technique for measuring adsorption isotherms. It was concluded that ethanol does not form adsorbed monolayers on the surface. Instead, it partitions onto the surface as a surface-enhanced local phase separation related to its poor solubility in alkane solvents.

Periodic ripples on thermally-annealed graphene on Cu (110)-reconstruction or moiré pattern?

We have used ultrahigh vacuum scanning tunneling microscopy (STM) to investigate the effect of thermal annealing of graphene grown by chemical vapor deposition on a Cu(110) foil. We show that the annealing appears to induce a reconstruction of the Cu surface along the [210] direction, with a period of 1.43 nm. Such reconstructions have been ascribed to the tensile strain induced in the Cu surface by its differential thermal expansion relative to the graphene over-layer, but we show that it is in fact a moiré pattern due to interference between the graphene and the underlying atomic lattice as evidenced by the appearance of an odd-even transition only observed due to misorientation of the top layer of a layered crystal. This highlights that the analysis of STM measurements of graphene on metal surfaces should take such interference effects into account and that the graphene-Cu interface is more complex than previously thought.

Electron transport behavior of quinoidal heteroacene-based junctions: effective electron-transport pathways and quantum interference.

The electron transport behavior through a series of molecular junctions composed of tetracene (TC) and S/O substituted-TC (S/O-TC) has been studied using density functional theory (DFT) combined with the non-equilibrium Green's function (NEGF) method. The unique transport behavior has been interpreted using correlated quantum interference and electron transport pathway models. In the TC system, two dominant electron transfer channels exist as demonstrated by a detailed transmission pathway analysis. In the substituted S/O-TC systems, the electron transport behavior is regulated through either constructive or destructive quantum interference due to the existence of additional p-electrons, leading to a significant diversity of current-voltage curves. Compared to the TC molecule in the bias region from 0 to 1.0 V, an α-connected molecular junction exhibits a greater current, whereas a ß-connected molecular junction shows a smaller current. The substitution with O and S atoms shows a minor effect on the conductance of the molecular junctions. In order to clarify the role of heteroatoms, a series of artificial models designed by removing specific sulfur and carbon atoms in α-S-TC have been investigated in detail. The results have demonstrated that only the S heteroatom on one side of the molecule contributes to the junction conductivity through constructive quantum interference. It has also been observed that current exchange occurs between the two electron transfer channels.

Recent advancements in the use of exosomes as drug delivery systems.

Extracellular vesicles (EVs) are the substances that are released by most types of cells and have an important role in cell to cell communication. Among the most highly researched EVs are exosome. Recent studies show that exosomes derived from cells have different roles and targets. Many studies show that exosome can efficiently deliver many different kinds of cargo to the target cell. Therefore, they are often used to deliver therapeutic cargo for treatment. The exosomes that have been used include both natural ones and those that have been modified with other substances to increase the delivery ability. This article provides a review of both exosomes derived from various cells and modified exosome and their ability in delivering the many kinds of cargo to the target cell.

The inverse problem in magnetic force microscopy--inferring sample magnetization from MFM images.

Nanomagnetic structures have the potential to surpass silicon's scaling limitations both as elements in hybrid CMOS logic and as novel computational elements. Magnetic force microscopy (MFM) offers a convenient characterization technique for use in the design of such nanomagnetic structures. MFM measures the magnetic field and not the sample's magnetization. As such the question of the uniqueness of the relationship between an external magnetic field and a magnetization distribution is a relevant one. To study this problem we present a simple algorithm which searches for magnetization distributions consistent with an external magnetic field and solutions to the micromagnetic equations' qualitative features. The algorithm is not computationally intensive and is found to be effective for our test cases. On the basis of our results we propose a systematic approach for interpreting MFM measurements.

Calibration of the spring constant of cantilevers of arbitrary shape using the phase signal in an atomic force microscope.

The measurement of cantilever parameters is an essential part of performing a calibrated measurement with an atomic force microscope (AFM). The thermal motion method is a widely used technique for calibrating the spring constant of an AFM cantilever, which can be applied to non-rectangular cantilevers. Given the trend towards high frequency scanning, calibration of non-rectangular cantilevers is of increasing importance. This paper presents two results relevant to cantilever calibration via the thermal motion method. We demonstrate the possibility of using the AFM's phase signal to acquire the thermal motion. This avoids the challenges associated with connecting the raw photodiode signal to a separate spectrum analyser. We also describe how numerical calculations may be used to calculate the parameters needed in a thermal motion calibration of a non-rectangular cantilever. Only accurate knowledge of the relative size of the in-plane dimensions of the cantilever is needed in this computation. We use this pair of results in the calibration of a variety of rectangular and non-rectangular cantilevers. We observe an average difference between the Sader and thermal motion values of cantilever stiffness of 10%.

Performing quantitative MFM measurements on soft magnetic nanostructures.

We have extended our previous work (Rawlings et al 2010 Phys. Rev. B 82 085404) on simulating magnetic force microscopy (MFM) images for magnetically soft samples to include an accurate representation of coated MFM tips. We used an array of square 500 nm nanomagnets to evaluate our improved MFM model. A quantitative comparison between model and experiment was performed for lift heights ranging from 20 to 100 nm. No fitting parameters were used in our comparison. For all lift heights the qualitative agreement between model and experiment was significantly improved. At low lift heights, where the magnetic signal was strong, the difference between theory and experiment was less than 30%.

Electrical actuation and readout in a nanoelectromechanical resonator based on a laterally suspended zinc oxide nanowire.

In this paper, we present experimental results describing enhanced readout of the vibratory response of a doubly clamped zinc oxide (ZnO) nanowire employing a purely electrical actuation and detection scheme. The measured response suggests that the piezoelectric and semiconducting properties of ZnO effectively enhance the motional current for electromechanical transduction. For a doubly clamped ZnO nanowire resonator with radius ~10 nm and length ~1.91 µm, a resonant frequency around 21.4 MHz is observed with a quality factor (Q) of ~358 in vacuum. A comparison with the Q obtained in air (~242) shows that these nano-scale devices may be operated in fluid as viscous damping is less significant at these length scales. Additionally, the suspended nanowire bridges show field effect transistor (FET) characteristics when the underlying silicon substrate is used as a gate electrode or using a lithographically patterned in-plane gate electrode. Moreover, the Young's modulus of ZnO nanowires is extracted from a static bending test performed on a nanowire cantilever using an AFM and the value is compared to that obtained from resonant frequency measurements of electrically addressed clamped­clamped beam nanowire resonators.

Unexpected controllable pair-structure in ferroelectric nanodomains.

The imminent inability of silicon-based memory devices to satisfy Moore's Law is approaching rapidly. Controllable nanodomains of ferroic systems are anticipated to enable future high-density nonvolatile memory and novel electronic devices. We find via piezoresponse force microscopy (PFM) studies on lead zirconate titanate (PZT) films an unexpected nanostructuring of ferroelectric-ferroelastic domains. These consist of c-nanodomains within a-nanodomains in proximity to a-nanodomains within c-domains. These structures are created and annihilated as pairs, controllably. We treat these as a new kind of vertex-antivertex pair and consider them in terms of the Srolovitz-Scott 4-state Potts model, which results in pairwise domain vertex instabilities that resemble the vortex-antivortex mechanism in ferromagnetism, as well as dislocation pairs (or disclination pairs) that are well-known in nematic liquid crystals. Finally, we show that these nanopairs can be scaled up to form arrays that are engineered at will, paving the way toward facilitating them to real technologies.

Site-specific variations in surface structure and Young's modulus of human hair surfaces at the nanometer scale as induced through bleach treatment.

The effect of bleach treatments on the morphology and mechanical properties of hair surfaces was measured at the nanometer scale using atomic force microscopy. We used an ultrahigh-precision relocation technique to observe the variations in these properties at precise locations on hair surfaces in their virgin state and then after each of the two bleach treatments, to rule out position-dependent fluctuations. We demonstrate that statistically significant variations in roughness and Young's modulus are observed as a result of exposure to bleach, which is known to disrupt the disulfide linkage network throughout the fiber. The rate at which surface roughness changes increased with the number of treatments, with very little effect seen after 10 min, and an increase of up to 65% was observed after a further 10 min. The Young's modulus decreased by up to 40% after each treatment. We also investigate micropores and show that they are subsurface, but revealed through bleaching, and oriented along the direction of the hair shaft with a characteristic aspect ratio. This work demonstrates the profound effect bleaching has on the molecular structure of hair, which manifests as changes in morphology and stiffness, and this should be taken into account in the formulation of future hair-care products.

Cadmium-induced dysfunction of the blood-brain barrier depends on ROS-mediated inhibition of PTPase activity in zebrafish.

Increasing evidence has demonstrated that cadmium accumulation in the blood increases the risk of neurological diseases. However, how cadmium breaks through the blood-brain barrier (BBB) and is transferred from the blood circulation into the central nervous system is still unclear. In this study, we examined the toxic effect of cadmium chloride (CdCl2) on the development and function of BBB in zebrafish. CdCl2 exposure induced cerebral hemorrhage, increased BBB permeability and promoted abnormal vascular formation by promoting VEGF production in zebrafish brain. Furthermore, in vivo and in vitro experiments showed that CdCl2 altered cell-cell junctional morphology by disrupting the proper localization of VE-cadherin and ZO-1. The potential mechanism involved in the inhibition of protein tyrosine phosphatase (PTPase) mediated by cadmium-induced ROS was confirmed with diphenylene iodonium (DPI), a ROS production inhibitor. Together, these data indicate that BBB is a critical target of cadmium toxicity and provide in vivo etiological evidence of cadmium-induced neurovascular disease in a zebrafish BBB model.

Recent advances of electrochemical sensors for detecting and monitoring ROS/RNS.

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are prominent metabolic products which show well-established significance. At relatively low concentrations, they play multifaceted roles in regulating a number of physiological processes. Overproduction of ROS/RNS contributes to the pathogenesis of a plethora of physiological disorders, including but not limited to cardiovascular diseases, neurodegenerative diseases, cancer. Electrochemistry have been extensively used for detecting and monitoring ROS/RNS, benefiting from their inherent advantages including fast response, low costs, real-time detection, high sensitivity and selectivity. This review focuses on three types of ROS/RNS (H2O2, O2-, NO) with emphasis on their electrochemical detection/monitoring respectively. We demonstrate the application of electrochemical strategies for ROS/RNS detection in body fluids, in vitro, and in vivo, outlining the hardware architecture and comparing analytical performance of these sensors. This review aims for a holistic view of limitations in existing ROS/RNS detection by comprehensively explaining the shortcomings of the current works in the hope of drawing attentions to the challenges of ROS/RNS electrochemical technologies. We pay particular attention to in vitro and in vivo sensors and extend our evaluation to suggest possible solutions. Specifically, this review focuses on the development of currently nanotechnologies, biomimetic engineering, 3D-culture methods and implanted sensors to provide a guideline for future works.

Photooxidation crosslinking to recover residual stress in decellularized blood vessel.

Decellularization method based on trypsin-digestion is widely used to construct small diameter vascular grafts. However, this method will reduce the opening angle of the blood vessel and result in the reduction of residual stress. Residual stress reduced has an adverse effect on the compliance and permeability of small diameter vascular grafts. To improve the situation, acellular blood vessels were treated with glutaraldehyde and photooxidation crosslinking respectively, and the changes of opening angle, circumferential residual strain of native blood vessels, decellularized arteries and crosslinked blood vessels were measured by means of histological examination, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in this study. The opening angle of decellularized arteries significantly restored after photooxidation crosslinking (P = 0.0216), while that of glutaraldehyde crosslinking blood vessels reduced. The elastic fibers inside the blood vessels became densely rearranged after photooxidation crosslinking. The results of finite element simulation showed that the residual stress increased with the increase of opening angle. In this study, we found at the first time that photooxidation crosslinking method could significantly increase the residual stress of decellularized vessels, which provides biomechanical support for the development of new biomaterials of vascular grafts.

Nanoparticles retard immune cells recruitment in vivo by inhibiting chemokine expression.

The large-scale utilization of nanotechnology depends on public and consumer confidence in the safety of this new technology. Studying the interaction of nanoparticles with immune cells plays a vital role in the safety assessment of nanomedicine. Although some researches have indicated that the immune cells undergo severe interfere after phagocytosis of nanoparticles, the impact on immune system of the whole body are still unclear. Here, we use immune cells labeled transgenic zebrafish to study the mechanisms of nanoparticles on zebrafish immune cells. We demonstrate that gold nanoparticles (Au NPs) phagocytized by immune cells can reduce and retard the sensitivity of immune response, resulting nanoparticle-induced bluntness in immune cell (NIBIC). RNA-seq and functional analysis reveal that NIBIC is mainly induced by the inhibiting expression of chemokine receptor 5 (CCR5). Furthermore, PVP-modified Au NPs can eliminate NIBIC by inhibiting the cell phagocytosis. Our results highlight the potential risk for Au NPs in vivo and further the understanding of the mechanism of the interaction between Au NPs and the immune response. We should consider this factor in future material design and pay more attention to the process of using nanomedicines on immune diseases.

Bundles of polytwins as meta-elastic domains in the thin polycrystalline simple multi-ferroic system PZT.

We used enhanced piezo-response force microscopy (E-PFM) to investigate both ferroelastic and ferroelectric nanodomains in thin films of the simple multi-ferroic system PbZr(0.3)Ti(0.7)O(3) (PZT). We show how the grains are organized into a new type of elastic domain bundles of the well-known periodic elastic twins. Here we present these bundle domains and discuss their stability and origin. Moreover, we show that they can arrange in such a way as to release strain in a more effective way than simple twinning. Finally, we show that these bundle domains can arrange to form the macroscopic ferroelectric domains that constitute the basis of ferroelectric-based memory devices.