Xenon gas field ion source from a single-atom tip.

Focused ion beam (FIB) systems have become powerful diagnostic and modification tools for nanoscience and nanotechnology. Gas field ion sources (GFISs) built from atomic-size emitters offer the highest brightness among all ion sources and thus can improve the spatial resolution of FIB systems. Here we show that the Ir/W(111) single-atom tip (SAT) can emit high-brightness Xe ion beams with a high current stability.

Adipocyte Ceramides Regulate Subcutaneous Adipose Browning, Inflammation, and Metabolism.

Adipocytes package incoming fatty acids into triglycerides and other glycerolipids, with only a fraction spilling into a parallel biosynthetic pathway that produces sphingolipids. Herein, we demonstrate that subcutaneous adipose tissue of type 2 diabetics contains considerably more sphingolipids than non-diabetic, BMI-matched counterparts. Whole-body and adipose tissue-specific inhibition/deletion of serine palmitoyltransferase (Sptlc), the first enzyme in the sphingolipid biosynthesis cascade, in mice markedly altered adipose morphology and metabolism, particularly in subcutaneous adipose tissue.

Fabrication of CoPt ultra-sharp single atom tips.

Two kinds of new nano tips with potential to magnetic application are fabricated. One is a PtCo alloy pyramidal tip formed by surface faceting, the other is a Pt based Co tip formed by the epitaxy with a proper growth mode. Ultra high vacuum-field ion microscopy with atomic resolution is used to investigate the atomic structures of the tip apex after various sharpen treatments.

Inhibitor binding increases the mechanical stability of staphylococcal nuclease.

Staphylococcal nuclease (SNase) catalyzes the hydrolysis of DNA and RNA in a calcium-dependent fashion. We used AFM-based single-molecule force spectroscopy to investigate the mechanical stability of SNase alone and in its complex with an SNase inhibitor, deoxythymidine 3',5'-bisphosphate. We found that the enzyme unfolds in an all-or-none fashion at ∼26 pN.

The role of tryptophan in staphylococcal nuclease stability.

Staphylococcal nuclease (SNase) has a single Trp residue at position 140. Circular dichroism, intrinsic and ANS-binding fluorescence, chemical titrations and enzymatic assays were used to measure the changes of its structure, stability and activities as the Trp was mutated or replaced to other positions. The results show that W140 is critical to SNase structure, stability, and function.

A single-atom sharp iridium tip as an emitter of gas field ion sources.

We report a reliable method for preparing a pure Ir single-atom tip by thermal treatment in oxygen. The atomic structure of the tip apex and its ion emission characteristics are investigated with field ion microscopy. We have shown that the Ir single-atom tip can be a good field ion emitter, capable of emitting a variety of gas ion beams, such as He+, H2+, N2+, and O2+, with high brightness and stability.

Phase contribution of image potential on empty quantum well States in pb islands on the cu(111) surface.

We use scanning tunneling spectroscopy to explore the quantum well states in the Pb islands grown on a Cu(111) surface. Our observation demonstrates that the empty quantum well states, whose energy levels lie beyond 1.2 eV above the Fermi level, are significantly affected by the image potential.

A fully coherent electron beam from a noble-metal covered W(111) single-atom emitter.

In quantum mechanics, a wavefunction contains two factors: the amplitude and the phase. Only when the probing beam is fully phase coherent, can complete information be retrieved from a particle beam based experiment. Here we use the electron beam field emitted from a noble-metal covered W(111) single-atom tip to image single-walled carbon nanotubes (SWNTs) in an electron point projection microscope (PPM).

Thermostability of the N-terminal RNA-binding domain of the SARS-CoV nucleocapsid protein: experiments and numerical simulations.

Differential scanning calorimetry, circular dichroism spectroscopy, nuclear magnetic resonance spectroscopy, and numerical simulations were used to study the thermostability of the N-terminal RNA-binding domain (RBD) of the SARS-CoV nucleocapsid protein. The transition temperature of the RBD in a mixing buffer, composed of glycine, sodium acetate, and sodium phosphate with 100 mM sodium chloride, at pH 6.8, determined by differential scanning calorimetry and circular dichroism, is 48.

Two-dimensional dopant profiling by electrostatic force microscopy using carbon nanotube modified cantilevers.

A two-dimensional (2D) dopant profiling technique is demonstrated in this work. We apply a unique cantilever probe in electrostatic force microscopy (EFM) modified by the attachment of a multiwalled carbon nanotube (MWNT). Furthermore, the tip apex of the MWNT was trimmed to the sharpness of a single-walled carbon nanotube (SWNT).

Hydrophobic condensation and modular assembly model of protein folding.

Despite several decades of intense study, protein folding problem remains elusive. In this paper, we review current knowledge and the prevailing thinking in the field, and summarize our work on the in vitro folding of a typical small globular protein, staphylococcal nuclease (SNase). Various thermodynamic and kinetic methods have been employed to determine the energetic and construct the energy landscape of folding.

Compact dimension of denatured states of staphylococcal nuclease.

Fluorescence and circular dichroism stopped-flow have been widely used to determine the kinetics of protein folding including folding rates and possible folding pathways. Yet, these measurements are not able to provide spatial information of protein folding/unfolding. Especially, conformations of denatured states cannot be elaborated in detail.

Manifestation of work function difference in high order Gundlach oscillation.

Gundlach oscillation (or the standing-wave state) is a general phenomenon manifesting in the tunneling spectrum acquired from a metal surface using scanning tunneling spectroscopy. Previous studies relate the energy shift between peaks of the lowest-order Gundlach oscillation observed on the thin film and the metal substrate to the difference in their work functions. By observing Gundlach oscillations on Ag/Au(111), Ag/Cu(111), and Co/Cu(111) systems, we demonstrate that the work function difference is not the energy shift of the lowest order but the ones of higher order where a constant energy shift exhibits.

A Markovian engine for a biological energy transducer: the catalytic wheel.

The molecular machines in biological cells are made of proteins, DNAs and other classes of molecules. The structures of these molecules are characteristically "soft", highly flexible, and yet their interactions with other molecules or ions are specific and selective. This chapter discusses a prevalent form, the catalytic wheel, or the energy transducer of cells, examines its mechanism of action, and extracts from it a set of simple but general rules for understanding the energetics of the biomolecular devices.

Magic numbers of atoms in surface-supported planar clusters.

Surface-supported planar clusters can sprout active research and create numerous applications in the realm of nanotechnology. Exploitation of these clusters will be more extended if their properties on a supported substrate are thoroughly apprehended, and if they can be fabricated in a controllable way. Here we report finding the magic numbers in two-dimensional Ag clusters grown on Pb quantum islands.

Antigen-based immunofluorescence analysis of B-cell targeting: advanced technology for the generation of novel monoclonal antibodies with high efficiency and selectivity.

On the basis of immunofluorescence analysis, an entire pathway of B-cell targeting was successfully identified, which can drive selective production of monoclonal antibodies with high efficiency and selectivity. The technique comprises three critical steps, antigen-based preselection of B lymphocytes, formation of antigenselected B lymphocyte and myeloma cell complexes, and selective fusion of B-cell-myeloma cell complexes with electrical pulses. Intriguingly, expression of surface immunoglobulin receptors on B lymphocytes was recognized even after immunization in vitro.

Rotary motor powered by stochastic uncorrelated dipoles.

It is demonstrated that the stochastic back-and-forth vibrations of uncorrelated dipoles may lead to rotation of their ambient dipoles. This peculiar phenomenon is clarified by considering spatial and temporal symmetry breakings. The former asymmetry is the result of the multiple biased Hamiltonian vector fields, which is a ratchet effect, and the latter, of the time sequence specified by a metastable state.

Local stability identification and the role of key acidic amino acid residues in staphylococcal nuclease unfolding.

Staphylococcal nuclease is a single domain protein with 149 amino acids. It has no disulfide bonds, which makes it a simple model for the study of protein folding. In this study, 20 mutants of this protein were generated each with a single base substitution of glycine for negatively charged glutamic acid or aspartic acid.

Local stability identification and the role of a key aromatic amino acid residue in staphylococcal nuclease refolding.

Staphylococcal nuclease (SNase) is a model protein that contains one domain and no disulfide bonds. Its stability in the native state may be maintained mainly by key amino acids. In this study, two point-mutated proteins each with a single base substitution [alanine for tryptophan (W140A) and alanine for lysine (K133A)] and two truncated fragment proteins (positions 1-139 [SNase(1-139) or W140O] and positions 1-141 [SNase(1-141) or E142O]) were generated.

Self-organized growth of nanopucks on Pb quantum islands.

Electronic Moirè patterns found on lead (Pb) quantum islands can serve as a template to grow self-organized cluster (nanopucks) arrays of various materials. These patterns can be divided into fcc- and hcp-stacked areas, which exhibit different binding strengths to the deposited adatoms. For Ag adatoms, the binding energy can differ substantially and the confined nucleation thus occurs in the fcc sites.

Two approaches toward a high-efficiency flashing ratchet.

For a flashing ratchet with periodic potentials fluctuating via random shifts of one-half period, a high efficiency is shown to result from two mechanisms. The previously reported one [Yu. A.

Hydrogen-adsorption induced atomic rearrangement of a Pb monolayer on Si(111).

We have observed interesting H-atom adsorption induced atomic rearrangements of a Pb monolayer on the Si(111) with a scanning tunneling microscope. A hexagonal ringlike pattern is formed around the point defect. The interactions among nearby H-adsorbed defects can even produce interferencelike superstructures.

Observation of finite-size effects on a structural phase transition of 2D nanoislands.

We study a reversible, temperature-driven structural surface phase transition of Pb/Si(111) nanoislands with a variable-temperature scanning tunneling microscope. Our quantitative measurements indicate that the transition temperature decreases with decreasing island and domain size. The boundaries of the nanoislands also influence the transition.