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Four-wheeled test drive Any future artificial transporters and robots operating at the nanoscale are likely to require molecules capable of directional translational movement over a surface. Even the design of such molecules is a daunting task, however, as they need to be able to use light, chemical or electrical energy to modulate their interaction with the surface in a way that generates directional motion. Kudernac et al . now unveil just such a molecule, made by attaching four rotary motor units to a central axis. Inelastic electron tunnelling induces conformational changes in the rotors and propels the molecule across a copper surface. By changing the direction of the rotary motion of individual motor units, the self-propelling molecular 'four-wheeler' structure can follow random or preferentially linear trajectories. This design provides a starting point for the exploration of more sophisticated molecular mechanical systems, perhaps with complete control over their direction of motion. Propelling single molecules in a controlled manner along an unmodified surface remains extremely challenging because it requires molecules that can use light, chemical or electrical energy to modulate their interaction with the surface in a way that generates motion. Nature’s motor proteins 1 , 2 have mastered the art of converting conformational changes into directed motion, and have inspired the design of artificial systems 3 such as DNA walkers 4 , 5 and light- and redox-driven molecular motors 6 , 7 , 8 , 9 , 10 , 11 . But although controlled movement of single molecules along a surface has been reported 12 , 13 , 14 , 15 , 16 , the molecules in these examples act as passive elements that either diffuse along a preferential direction with equal probability for forward and backward movement or are dragged by an STM tip. Here we present a molecule with four functional units—our previously reported rotary motors 6 , 8 , 17 —that undergo continuous and defined conformational changes upon sequential electronic and vibrational excitation. Scanning tunnelling microscopy confirms that activation of the conformational changes of the rotors through inelastic electron tunnelling propels the molecule unidirectionally across a Cu(111) surface. The system can be adapted to follow either linear or random surface trajectories or to remain stationary, by tuning the chirality of the individual motor units. Our design provides a starting point for the exploration of more sophisticated molecular mechanical systems with directionally controlled motion.

Name that atom Dynamic force microscopy, which works by detecting the interaction force between the oscillating tip of an atomic force microscope (AFM) and a surface, has been refined to the extent that it can achieve true atomic resolution of insulator, semiconductor and metal surfaces. In a landmark publication in this issue this technique has been used to perform the chemical identification of individual atoms in a multi-element system. The method involves precise quantification of short-range chemical forces between the probed atoms and the AFM tip, and provides a robust and general recognition tool suitable for both cryogenic and room temperature environments. The cover shows a topographic image of a surface alloy made up of silicon (red), tin (blue), and lead atoms (green) in equal proportions on a silicon (111) substrate. This atomic identification method is relevant to a wide range of research areas such as catalysis, materials science and semiconductor technology. Scanning probe microscopy is a versatile and powerful method that uses sharp tips to image, measure and manipulate matter at surfaces with atomic resolution 1 , 2 . At cryogenic temperatures, scanning probe microscopy can even provide electron tunnelling spectra that serve as fingerprints of the vibrational properties of adsorbed molecules 3 , 4 , 5 and of the electronic properties of magnetic impurity atoms 6 , 7 , thereby allowing chemical identification. But in many instances, and particularly for insulating systems, determining the exact chemical composition of surfaces or nanostructures remains a considerable challenge. In principle, dynamic force microscopy should make it possible to overcome this problem: it can image insulator, semiconductor and metal surfaces with true atomic resolution 8 , 9 , 10 , by detecting and precisely measuring 11 , 12 , 13 the short-range forces that arise with the onset of chemical bonding between the tip and surface atoms 14 , 15 and that depend sensitively on the chemical identity of the atoms involved. Here we report precise measurements of such short-range chemical forces, and show that their dependence on the force microscope tip used can be overcome through a normalization procedure. This allows us to use the chemical force measurements as the basis for atomic recognition, even at room temperature. We illustrate the performance of this approach by imaging the surface of a particularly challenging alloy system and successfully identifying the three constituent atomic species silicon, tin and lead, even though these exhibit very similar chemical properties and identical surface position preferences that render any discrimination attempt based on topographic measurements impossible.

Extracellular vesicles (EVs) are cell-to-cell shuttles that have recently drawn interest both as drug delivery platforms and disease biomarkers. Despite the increasingly recognized relevance of these vesicles, their detection, and characterization still have several technical drawbacks. In this paper, we accurately assess the size distribution and concentration of EVs by using a high-throughput non-perturbative technique such as Dynamic Light Scattering (DLS). The vesicle radii distribution, as further confirmed by Atomic Force Microscopy experiments, ranges from 10 to 80 nm and appears very asymmetric towards larger radii with a main peak at roughly 30 nm. By combining DLS and Bradford assay, we also demonstrate the feasibility of recovering the concentration and its distribution of proteins contained inside vesicles. The sensitivity of our approach allows to detect protein concentrations as low as 0.01 mg/ml.

The emergence of resistance to multiple unrelated chemotherapeutic drugs impedes the treatment of several cancers. Although the involvement of ATP-binding cassette transporters has long been known, there is no in situ method capable of tracking this transporter-related resistance at the single-cell level without interfering with the cell’s environment or metabolism. Here, we demonstrate that scanning electrochemical microscopy (SECM) can quantitatively and noninvasively track multidrug resistance-related protein 1–dependent multidrug resistance in patterned adenocarcinoma cervical cancer cells. Nonresistant human cancer cells and their multidrug resistant variants are arranged in a side-by-side format using a stencil-based patterning scheme, allowing for precise positioning of target cells underneath the SECM sensor. SECM measurements of the patterned cells, performed with ferrocenemethanol and [Ru(NH ₃) ₆] ³⁺ serving as electrochemical indicators, are used to establish a kinetic “map” of constant-height SECM scans, free of topography contributions. The concept underlying the work described herein may help evaluate the effectiveness of treatment administration strategies targeting reduced drug efflux.

The invention of the scanning tunnelling microscope 25 years ago, followed by the arrival of the atomic force microscope five years later, were crucial events in the history of nanoscience and nanotechnology. As the recent International Conference on Nanoscience and Technology in Basel made clear, scanning probe microscopes based on these discoveries are still having a tremendous impact on many areas of research.

Biosynthesis of copper, zero-valent iron (ZVI), and silver nanoparticles using leaf extract of Dodonaea viscosa has been investigated in this report. There are no additional surfactants/polymers used as capping or reducing agents for these syntheses. The synthesized nanoparticles were characterized by UV–Vis spectroscopy, X-ray diffraction, atomic force microscopy, and high-resolution transmission electron microscopy. The phase analysis was performed using selected area electron diffraction. The pH dependence of surface plasmon resonance and subsequent size variation has been determined. The synthesized nanoparticles showed spherical morphology and the average size of 29, 27, and 16 nm for Cu, ZVI, and Ag nanoparticles, respectively. Finally, biosynthesized Cu, ZVI, and Ag nanoparticles were tested against human pathogens viz. Gram-negative Escherichia coli, Klebsiella pneumonia, Pseudomonas fluorescens and Gram-positive Staphylococcus aureus and Bacillus subtilis , and showed good antimicrobial activity.

Small-diameter (1 to 7 nanometers) silicon nanowires (SiNWs) were prepared, and their surfaces were removed of oxide and terminated with hydrogen by a hydrofluoric acid dip. Scanning tunneling microscopy (STM) of these SiNWs, performed both in air and in ultrahigh vacuum, revealed atomically resolved images that can be interpreted as hydrogen-terminated Si (111)-(1 x 1) and Si (001)-(1 x 1) surfaces corresponding to$SiH_3$on Si (111) and$SiH_2$on Si (001), respectively. These hydrogen-terminated SiNW surfaces seem to be more oxidation-resistant than regular silicon wafer surfaces, because atomically resolved STM images of SiNWs were obtained in air after several days' exposure to the ambient environment. Scanning tunneling spectroscopy measurements were performed on the oxide-removed SiNWs and were used to evaluate the electronic energy gaps. The energy gaps were found to increase with decreasing SiNW diameter from 1.1 electron volts for 7 nanometers to 3.5 electron volts for 1.3 nanometers, in agreement with previous theoretical predictions.

Scanning nonlinear dielectric microscopy (SNDM) is a near-field microwave-based scanning probe microscopy method with a wide variety of applications, especially in the fields of dielectrics and semiconductors. This microscopy method has often been combined with contact-mode atomic force microscopy (AFM) for simultaneous topography imaging and contact force regulation. The combination SNDM with intermittent contact AFM is also beneficial for imaging a sample prone to damage and using a sharp microscopy tip for improving spatial resolution. However, SNDM with intermittent contact AFM can suffer from a lower signal-to-noise (S/N) ratio than that with contact-mode AFM because of the shorter contact time for a given measurement time. In order to improve the S/N ratio, we apply boxcar averaging based signal acquisition suitable for SNDM with intermittent contact AFM. We develop a theory for the S/N ratio of SNDM and experimentally demonstrate the enhancement of the S/N ratio in SNDM combined with peak-force tapping (a trademark of Bruker) AFM. In addition, we apply the proposed method to the carrier concentration distribution imaging of atomically thin van der Waals semiconductors. The proposed method clearly visualizes an anomalous electron doping effect on few-layer Nb-doped MoS2. The proposed method is also applicable to other scanning near-field microwave microscopes combined with peak-force tapping AFM such as scanning microwave impedance microscopy. Our results indicate the possibility of simultaneous nanoscale topographic, electrical, and mechanical imaging even on delicate samples.

Defects such as oxygen vacancies play a crucial role in the surface properties of transition metal oxides. By means of time-resolved, high-resolution scanning tunneling microscopy, we unraveled an adsorbate-mediated diffusion mechanism of oxygen vacancies on rutile TiO2(110). Adsorbed oxygen molecules mediate vacancy diffusion through the loss of an oxygen atom to a vacancy and the sequential capture of an oxygen atom from a neighboring bridging oxygen row, leading to an anisotropic oxygen vacancy diffusion pathway perpendicular to the bridging oxygen rows.

The restoration of defective bone tissue and complications related to surgery and fracture site infection are major concerns in orthopedic surgeries. However, it is crucial to develop osteoconductive and bacteriostatic composites. Chitosan/nano hydroxyapatite (CT/n-HAp) powder containing of Ag and Si were prepared by an in situ hybridization method. The aim of this work was to elucidate the effect of size, surface roughness, and chemical structure of mentioned nanocomposites on cytotoxicity and bacteriostatic activity via human osteoblast cells and Escherichia Coli, respectively. Particle size, surface roughness, reactive oxygen specious production, and bioactivity of nanocomposites were investigated by X ray diffraction, atomic force microscopy, DPPH assay, and SEM/UV–Visible spectrophotometer, respectively. Bacterial colony counting test, MTT assay and lactate dehydrogenase (LDH) release were performed as bacteriostatic and biocompatibility tests. The results showed that CT/n-HAp/Ag with smaller particle size in the range of 1–22.6 nm (10.00 ± 0.09 nm) than CT/n-HAp/Si in the range of 3–72.5 nm (18.00 ± 0.14 nm) exhibits higher cell viability and bacteriostatic activity, and less LDH release from cell plasma membrane. Integration of Ag into the nanocomposite hindered the release of Ag+ ions and restricts cytotoxic potential on cells. Higher cytotoxic effect of CT/n-HAp/Si might be related to proton concentration derived from nanocomposite and its chemical structure. In conclusion, the strong bone regeneration potential of CT/n-HAp and good biocompatibility and bacteriostatic activity of CT/n-HAp/Ag make it as potential bacteriostatic bone filler in site of infected bone fracture.