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Breast cancer cells secrete abundant nanometer-sized vesicles. Small extracellular vesicle (or sEV) cargos are known to have similar biomolecular signatures to their secreting parental breast cance...

Self-organization of cytoskeletal proteins such as actin and tubulin into filaments and microtubules is frequently assisted by the proteins binding to them. Formins are regulatory proteins that nucleate the formation of new filaments and are essential for a wide range of cellular functions. The vertebrate inverted formin 2 (INF2) has both actin filament nucleating and severing/depolymerizing activities connected to its ability to encircle actin filaments. Using atomic force microscopy, we report that a formin homology 2 (FH2) domain-containing construct of INF2 (INF2-FH1-FH2-C or INF2-FFC) self-assembles into nanoscale ringlike oligomeric structures in the absence of actin filaments, demonstrating an inherent ability to reorganize from a dimeric to an oligomeric state. A construct lacking the C-terminal region (INF2-FH1-FH2 or INF2-FF) also oligomerizes, confirming the dominant role of FH2-mediated interactions. Moreover, INF2-FFC domains were observed to organize into ringlike structures around single actin filaments. This is the first demonstration that formin FH2 domains can self-assemble into oligomers in the absence of filaments and has important implications for observing unaveraged decoration and/or remodeling of filaments by actin binding proteins. © 2014 American Chemical Society.

A morphological transition from dendrites to nanowires in the electroless deposition of silver by galvanic displacement of copper seeds is investigated as a function of seed size. The transition to...

A potential route to extend Moore's law beyond the physical limits of existing materials and device architectures is to achieve nanotechnology breakthroughs in materials and device concepts. Here, we discuss an on-demand WO(3-x)-based nanoionic device where electrical and neuromorphic multifunctions are realized through externally induced local migration of oxygen ions. The device is found to possess a wide range of time scales of memorization, resistance switching, and rectification varying from volatile to permanent in a single device, and these can furthermore be realizable in both two- or three-terminal systems. The gradually changing volatile and nonvolatile resistance states are experimentally demonstrated to mimic the human brain's forgetting process for short-term memory and long-term memory.We propose this nanoionic device with its on-demand electrical and neuromorphic multifunction has a unique paradigm shifting potential for the fabrication of configurable circuits, analog memories, digital-neural fused networks, and more in one device architecture.

Key to single-molecule electronics is connecting functional molecules to each other using conductive nanowires. This involves two issues: how to create conductive nanowires at designated positions, and how to ensure chemical bonding between the nanowires and functional molecules. Here, we present a novel method that solves both issues. Relevant functional molecules are placed on a self-assembled monolayer of diacetylene compound. A probe tip of a scanning tunneling microscope is then positioned on the molecular row of the diacetylene compound to which the functional molecule is adsorbed, and a conductive polydiacetylene nanowire is fabricated by initiating chain polymerization by stimulation with the tip. Since the front edge of chain polymerization necessarily has a reactive chemical species, the created polymer nanowire forms chemical bonding with an encountered molecular element. We name this spontaneous reaction "chemical soldering". First-principles theoretical calculations are used to investigate the structures and electronic properties of the connection. We demonstrate that two conductive polymer nanowires are connected to a single phthalocyanine molecule. A resonant tunneling diode formed by this method is discussed.

The pursuit of methods for design and preparation of robust nanoarchitectonic systems with integrated functionality through bottom-up methodologies remains a driving force in molecular nanotechnology. Through the use of π-conjugated covalent bonds, we demonstrate a general substrate-mediated, soft solution methodology for the preparation of extended π-conjugated polymeric nanoarchitectures in low-dimensions. Based on thermodynamic control over equilibrium polymerization at the solid-liquid interface whereby aromatic building blocks spontaneously and selectively link, close-packed arrays composed of one-dimensional (1-D) aromatic polymers and two-dimensional (2-D) macromolecular frameworks have been prepared and characterized by in situ scanning tunneling microscopy. This methodology eliminates the necessity for severe conditions and sophisticated equipment common to most current fabrication techniques and imparts almost infinite possibilities for the preparation of robust materials with designer molecular architectures.

The atomic structure of graphene on polycrystalline copper substrates has been studied using scanning tunneling microscopy. The graphene overlayer maintains a continuous pristine atomic structure over atomically flat planes, monatomic steps, edges, and vertices of the copper surface. We find that facets of different identities are overgrown with graphene's perfect carbon honeycomb lattice. Our observations suggest that growth models including a stagnant catalytic surface do not apply to graphene growth on copper. Contrary to current expectations, these results reveal that the growth of macroscopic pristine graphene is not limited by the underlying copper structure.

Engineered planar substrates, such as chemically-derivatized glass, silicon/silicon oxide, and gold-thiol-based self assembled monolayers (SAMs) are critical enabling components in widely used and commercially important technologies such as ‘next gen’ DNA sequencing9, 10, nucleic acid microarrays11, and surface plasmon resonance biosensors (Biacore, etc)12. Because most of these technologies employ far-field optical microscopy or photonic detection, surface topography and nanometer-scale variations in surface chemistry of the substrate is not of concern. However, in scanning probe microscopy of nucleic acids and nucleic acid-protein complexes, substrate surface topography and local physico-chemical properties are critical issues. When used with the proper attention to substrate:sample preparation, scanning probe microscopy offers substantial advantages over photonic detection in terms of sensitivity (no labels), resolution (sub-molecular-to-atomic) and breadth of measurement modalities (topography, stiffness, adhesiveness, as well as thermal and electrostatic properties). Paradoxically, substrates used in scanning probe microscopy tend to be less engineered and less well characterized than are scaffolds and surfaces used in systems with photonic detection. This is particularly true in the of study of biopolymers, such as DNA and protein fibers of various kinds, which can be microns-to-millimeters in length and thus require vast areas of atomically-flat surface that can be very difficult to achieve on chemically modified glass or gold:thiol:SAM substrates. Freshly cleaved mica complexed with multi-valent cations is a very popular but simple system used to bind DNA for AFM imaging in liquid and in air. In particular, Nickel (II) ion, applied in the form of an aqueous chloride or nitrate salt solution, has been shown to produce unusually strong DNA adsorption on mica compared to similar divalent metal ions and this has been used to advantage in a number of studies, including our own13, where strong adsorption is required1, 4. Despite Ni:mica’s widespread use by the AFM community and its potential as a substrate for DNA nanotechnologies of various kinds, knowledge of its nanoscale physico-chemistry is limited. A series of classic studies used surface force apparatus (SFA) to study the interaction between two cleaved mica surfaces in various mono- and divalent aqueous metal-ion electrolytes14, 15 (though not including Ni2+). These authors analyzed the mica-mica interaction in terms of an extended DLVO theory of colloid stability. Notably, their experiments were mostly conducted at pH 5.8. Workers studying the biochemistry of single DNA molecules bound to mica with AFM have extended this classic SFA-based work, using a generalization of the DLVO theory to model the force interaction of a charged DNA molecule and mica surface, rather than two mica surfaces, in aqueous metal ion electrolytes at physiological pH (7.0–8.5)4, 5, 7, 8. However, metal ions in solution are known to exhibit complex speciation behavior16, and this important aspect of metal ion chemistry has not been taken into account in the past modeling and discussion of DNA binding to mica. Further, the nickel-ion treated mica surface itself has not been directly characterized due to the minute quantities of material involved. In this report, we use a combination of nanoscale analytical techniques to probe the properties of Ni:mica on the molecular scale. We employ an exquisitely sensitive surface analysis technique, secondary ion mass spectrometry to confirm in situ partial ion exchange between Ni2+ in the solution and native K+ present on the untreated mica surface. Using AFM we show that a smooth, stable but difficult-to-detect molecular monolayer can form on mica treated with aqueous NiCl2 at pH ~7, likely a result of metal or metal-hydroxide precipitates. Importantly, this result indicates that the actual substrate:molecule interaction can be mediated in some cases by a molecular adlayer of different physico-chemical properties than the mica itself. We present thermodynamic simulations which show that nickel-ion speciation in aqueous solutions is highly sensitive to pH in the range 6–8. As a consequence the solution concentration of the divalent species can vary widely from what is assumed, and the speciation of other metal ions-complexes can be unpredictable unless great care is taken to stabilize the pH condition and redox condition of the solution. Taken together, our simulation and experimental results strongly suggest more detailed modeling and experiments are needed to properly understand and control the mica:metal-ion:DNA system at physiological pH. In order to determine the biofunctional characteristics of the Ni:mica surfaces we digested mica-adsorbed plasmid DNA with a restriction enzyme, RsaI. We show that Ni:mica is compatible with enzymology conducted directly on the surface-fixed DNA molecules, and can be used to precisely locate DNA sequence motifs within single molecules17. Similarly, it has potential uses as a scaffold or substrate for engineering DNA nanostructures and in other areas of DNA nanotechnology, like single molecule DNA sequencing.

We present an interferometric imaging technique that permits local measurement of mechanical properties and nanomechancial motion in small living animals. Measurements of nanomechanical properties and spatially resolved pulsations of

Nanoparticle chain aggregates are used as reinforcing fillers in elastomers (rubber) and significantly enhance the mechanical properties (tensile strength, Young's modulus) of elastomers. Insight into mechanisms of the performance of nanoparticle chain aggregates can be obtained from force vs displacement (force spectroscopy) measurements made with an AFM tip and an aggregate-coated substrate. Distinctive sawtooth patterns were observed which were interpreted as aggregate stretching and breaking events. Based on the measurements, estimates of the aggregate nanomechanical properties were made.

The interfacial stress of self-assembled monolayers on Au exposed to buffers of various pH values and ionic strengths is measured as a function of the liquid environment. The method uses two thiol-modified Au-covered silicon cantilevers and a differential method to compensate for thermal and refractive index changes of the liquid environment. Increasing pH and ionic strength leads to a bending, i.e., a compressive stress, of a mercaptohexadecanoic acid-covered cantilever compared to a hexadecanethiol-covered reference cantilever. In addition, the interfacial stress is found to be highly dependent on the surface density of the ionizeable mercaptohexadecanoic acid molecules when they are coadsorbed with hexadecanethiols on Au.

To help understand the anomalously low basicity of arsabenzene and phosphabenzene we have investigated the cor- relation between the core-ionization energies and proton affinities for arsabenzene, phosphabenzene, arsine, trimethylarsine, phosphine, and the methylphosphines. The results support the view that the low basicity is due to the inability of the aromatic compounds to undergo geometric rearrangement on protonation. Comparison of the Auger kinetic energies with core-ioniza- tion energies gives an estimate of 0.45 eV for the stabilization energy due to the resonance delocalization of the charge on phos- phine following core ionization. Further comparison of these quantities indicates that a methyl group and an aromatic ring are both electron donating compared to hydrogen.