Tunable near-infrared and visible-light transmittance in nanocrystal-in-glass composites

Amorphous metal oxides are useful in optical^1, 2, electronic^3, 4, 5 and electrochemical devices^6, 7. The bonding arrangement within these glasses largely determines their properties, yet it remains a challenge to manipulate their structures in a controlled manner. Recently, we developed synthetic protocols for incorporating nanocrystals that are covalently bonded into amorphous materials^8, 9. This ‘nanocrystal-in-glass’ approach not only combines two functional components in one material, but also the covalent link enables us to manipulate the glass structure to change its properties. Here we illustrate the power of this approach by introducing tin-doped indium oxide nanocrystals into niobium oxide glass (NbOx), and realize a new amorphous structure as a consequence of linking it to the nanocrystals. The resulting material demonstrates a previously unrealized optical switching behaviour that will enable the dynamic control of solar radiation transmittance through windows. These transparent films can block near-infrared and visible light selectively and independently by varying the applied electrochemical voltage over a range of 2.5 volts. We also show that the reconstructed NbOx glass has superior properties—its optical contrast is enhanced fivefold and it has excellent electrochemical stability, with 96 per cent of charge capacity retained after 2,000 cycles.

Synthetic Self-Localizing Ligands That Control the Spatial Location of Proteins in Living Cells

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja4046907

Publication Date (Web): August 14, 2013

Small-molecule ligands that control the spatial location of proteins in living cells would be valuable tools for regulating biological systems. However, the creation of such molecules remains almost unexplored because of the lack of a design methodology. Here we introduce a conceptually new type of synthetic ligands, self-localizing ligands (SLLs), which spontaneously localize to specific subcellular regions in mammalian cells. We show that SLLs bind their target proteins and relocate (tether) them rapidly from the cytoplasm to their targeting sites, thus serving as synthetic protein translocators. SLL-induced protein translocation enables us to manipulate diverse synthetic/endogenous signaling pathways. The method is also applicable to reversible protein translocation and allows control of multiple proteins at different times and locations in the same cell. These results demonstrate the usefulness of SLLs in the spatial (and temporal) control of intracellular protein distribution and biological processes, opening a new direction in the design of small-molecule tools or drugs for cell regulation.

Cell bilayer - protein interaction visualized under confocal fluorescence microscope

Membrane bending by protein–protein crowding

Nature Cell Biology

14,

944–949

(2012)

doi:10.1038/ncb2561

Received: 07 October 2011
Accepted: 12 July 2012
Published online: 19 August 2012

Curved membranes are an essential feature of dynamic cellular structures, including endocytic pits, filopodia protrusions and most organelles^1, 2. It has been proposed that specialized proteins induce curvature by binding to membranes through two primary mechanisms: membrane scaffolding by curved proteins or complexes^3, 4; and insertion of wedge-like amphipathic helices into the membrane^5, 6. Recent computational studies have raised questions about the efficiency of the helix-insertion mechanism, predicting that proteins must cover nearly 100% of the membrane surface to generate high curvature^7, 8, 9, an improbable physiological situation. Thus, at present, we lack a sufficient physical explanation of how protein attachment bends membranes efficiently. On the basis of studies of and , proteins involved in clathrin-mediated endocytosis, we propose a third general mechanism for bending fluid cellular membranes: protein–protein crowding. By correlating membrane tubulation with measurements of protein densities on membrane surfaces, we demonstrate that lateral pressure generated by collisions between bound proteins drives bending. Whether proteins attach by inserting a helix or by binding lipid heads with an engineered tag, protein coverage above ~20% is sufficient to bend membranes. Consistent with this crowding mechanism, we find that even proteins unrelated to membrane curvature, such as green fluorescent protein (GFP), can bend membranes when sufficiently concentrated. These findings demonstrate a highly efficient mechanism by which the crowded protein environment on the surface of cellular membranes can contribute to membrane shape change.

Mechanical Properties of Giant Liposomes Compressed between Two Parallel Plates: Impact of Artificial Actin Shells

Edith Schäfer , Torben-Tobias Kliesch , and Andreas Janshoff *
Institute of Physical Chemistry, Georg-August-University of Goettingen, Tammannstr. 6, 37077 Goettingen

Langmuir, Article ASAP
DOI: 10.1021/la401969t
Publication Date (Web): July 19, 2013
Copyright © 2013 American Chemical Society

The mechanical response of giant liposomes to compression between two parallel plates is investigated in the context of an artificial actin cortex adjacent to the inner leaflet of the bilayer. We found that nonlinear membrane theory neglecting the impact of bending sufficiently describes the mechanical response of liposomes consisting of fluid lipids to compression whereas the formation of an actin cortex or the use of gel-phase lipids generally leads to substantial stiffening of the shell. Giant vesicles are gently adsorbed on glassy surfaces and are compressed with tipless cantilevers using an atomic force microscope. Force–compression curves display a nonlinear response that allows us to determine the membrane tension σ0 and the area compressibility modulus KA by computing the contour of the vesicle as a function of the compression depth. The values for KA of fluid membranes correspond well to what is known from micropipet-suction experiments and computed from monitoring membrane undulations. The presence of a thick actin shell adjacent to the inner leaflet of the liposome membrane stiffens the system considerably, as mirrored in a significantly higher apparent area compressibility modulus.

Fabricating Nanoscale Chemical Gradients with ThermoChemical NanoLithography

Keith M. Carroll †‡, Anthony J. Giordano §, Debin Wang , Vamsi K. Kodali , Jan Scrimgeour †‡, William P. King #, Seth R. Marder §, Elisa Riedo †§, and Jennifer E. Curtis *†‡

Langmuir, 2013, 29 (27), pp 8675–8682

DOI: 10.1021/la400996w

Publication Date (Web): June 10, 2013

Production of chemical concentration gradients on the submicrometer scale remains a formidable challenge, despite the broad range of potential applications and their ubiquity throughout nature. We present a strategy to quantitatively prescribe spatial variations in functional group concentration using ThermoChemical NanoLithography (TCNL). The approach uses a heated cantilever to drive a localized nanoscale chemical reaction at an interface, where a reactant is transformed into a product. We show using friction force microscopy that localized gradients in the product concentration have a spatial resolution of 20 nm where the entire concentration profile is confined to sub-180 nm. To gain quantitative control over the concentration, we introduce a chemical kinetics model of the thermally driven nanoreaction that shows excellent agreement with experiments. The comparison provides a calibration of the nonlinear dependence of product concentration versus temperature, which we use to design two-dimensional temperature maps encoding the prescription for linear and nonlinear gradients. The resultant chemical nanopatterns show high fidelity to the user-defined patterns, including the ability to realize complex chemical patterns with arbitrary variations in peak concentration with a spatial resolution of 180 nm or better. While this work focuses on producing chemical gradients of amine groups, other functionalities are a straightforward modification. We envision that using the basic scheme introduced here, quantitative TCNL will be capable of patterning gradients of other exploitable physical or chemical properties such as fluorescence in conjugated polymers and conductivity in graphene. The access to submicrometer chemical concentration and gradient patterning provides a new dimension of control for nanolithography.

Bubbles are the new lenses for nanoscale light beams

These are laboratory images of a light beam without a bubble lens, followed by three examples of different bubble lenses altering the light. Credit: Tony Jun Huang, Penn State

Read more at: http://phys.org/news/2013-08-lenses-nanoscale.html#jCp

Anisotropic Nanoparticles as Shape-Directing Catalysts for the Chemical Etching of Silicon

Guoliang Liu †, Kaylie L. Young †, Xing Liao ‡, Michelle L. Personick †, and Chad A. Mirkin *†‡
†Department of Chemistry and International Institute for Nanotechnology and ‡Department of Materials Science and Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States

J. Am. Chem. Soc., Article ASAP
DOI: 10.1021/ja4061867
Publication Date (Web): August 1, 2013
Copyright © 2013 American Chemical Society

Anisotropic Au nanoparticles have been used to create a library of complex features on silicon surfaces. The technique provides control over feature size, shape, and depth. Moreover, a detailed study of the etching rate as a function of the nanoparticle surface facet interfaced with the silicon substrate suggested that the etching is highly dependent upon the facet surface energy. Specifically, the etching rate for Au nanocubes with {100}-terminated facets was 1.5 times higher than that for triangular nanoprisms with {111} facets. Furthermore, this work gives fundamental insight into the mechanism of metal-catalyzed chemical etching.

Plasma membrane (cell) fusion

Optical Fusion Assay Based on Membrane-Coated Spheres in a 2D Assembly

J. Am. Chem. Soc., Article ASAP

DOI: 10.1021/ja404071z

Publication Date (Web): August 5, 2013

A major goal in neurophysiology and research on enveloped viruses is to understand and control the biology and physics of membrane fusion and its inhibition as a function of lipid and protein composition. This poses an experimental challenge in the realization of fast and reliable assays that allow us, with a minimal use of fluorescent or radioactive labels, to identify the different stages of membrane–membrane interaction ranging from docking to complete membrane merging. Here, an optical two-dimensional fusion assay based on monodisperse membrane-coated microspheres is introduced, allowing unequivocal assignment of docking and membrane fusion. The hard-sphere fluid captures and quantifies relevant stages of membrane fusion and its inhibition without interference from aggregation, liposome rupture, extensive fluorescence labeling, and light scattering. The feasibility of the approach is demonstrated by using an established model system based on coiled-coil heterodimers formed between two opposing membrane-coated microspheres.

Mass spectrometry of Volatile Organic Compounds (VOCs)

Active Atmosphere-Ecosystem Exchange of the Vast Majority of Detected Volatile Organic Compounds

Science 9 August 2013:
Vol. 341 no. 6146 pp. 643-647

DOI: 10.1126/science.1235053

Numerous volatile organic compounds (VOCs) exist in Earth’s atmosphere, most of which originate from biogenic emissions. Despite VOCs’ critical role in tropospheric chemistry, studies for evaluating their atmosphere-ecosystem exchange (emission and deposition) have been limited to a few dominant compounds owing to a lack of appropriate measurement techniques. Using a high–mass resolution proton transfer reaction–time of flight–mass spectrometer and an absolute value eddy-covariance method, we directly measured 186 organic ions with net deposition, and 494 that have bidirectional flux. This observation of active atmosphere-ecosystem exchange of the vast majority of detected VOCs poses a challenge to current emission, air quality, and global climate models, which do not account for this extremely large range of compounds. This observation also provides new insight for understanding the atmospheric VOC budget.

Nanometre-scale thermometry in a living cell

Nature

500,

54–58

(01 August 2013)

doi:10.1038/nature12373

Received: 19 March 2013
Accepted: 10 June 2013
Published online: 31 July 2013

Sensitive probing of temperature variations on nanometre scales is an outstanding challenge in many areas of modern science and technology¹. In particular, a thermometer capable of subdegree temperature resolution over a large range of temperatures as well as integration within a living system could provide a powerful new tool in many areas of biological, physical and chemical research. Possibilities range from the temperature-induced control of gene expression^{2, 3, 4, 5} and tumour metabolism⁶ to the cell-selective treatment of disease^7, 8 and the study of heat dissipation in integrated circuits¹. By combining local light-induced heat sources with sensitive nanoscale thermometry, it may also be possible to engineer biological processes at the subcellular level^{2, 3, 4, 5}. Here we demonstrate a new approach to nanoscale thermometry that uses coherent manipulation of the electronic spin associated with nitrogen–vacancy colour centres in diamond. Our technique makes it possible to detect temperature variations as small as 1.8 mK (a sensitivity of 9 mK Hz^−1/2) in an ultrapure bulk diamond sample. Using nitrogen–vacancy centres in diamond nanocrystals (nanodiamonds), we directly measure the local thermal environment on length scales as short as 200 nanometres. Finally, by introducing both nanodiamonds and gold nanoparticles into a single human embryonic fibroblast, we demonstrate temperature-gradient control and mapping at the subcellular level, enabling unique potential applications in life sciences.

Why Male Mammals Are Monogamous

Science 2 August 2013:
Vol. 341 no. 6145 pp. 469-470
DOI: 10.1126/science.1242001

Monogamy has long fascinated scientists and the general public alike (1). Its occurrence in fellow mammalian species has puzzled evolutionary biologists (2–4). Male mammals have a much higher potential for producing offspring per unit time than females, making it necessary to identify selective advantages that would more than compensate for the loss of potential reproduction suffered by males that confine their reproductive activities to a single female. On page 526 of this issue, Lukas and Clutton-Brock (5) show that the costs of monogamy for males are not compensated by fitness benefits through paternal care. Instead, by forming pairs, males overcome disadvantages that arise because ecological factors promote wide spacing of individual females.