We present experimental support for a model of abalone nacre growth that is based on mineral bridges between successive aragonite tablets rather than on heteroepitaxial nucleation. Interlamellar sheets of organic polymers delineate the aragonite tablets but allow the tablets to grow mineral bridges through pores in the sheets. Atomic force microscope images of interlamellar organic sheets from flat pearls made by Haliotis rufescens (red abalone; marine gastropod mollusk) reveal a fibrous core and holes of 5-50 nm in diameter. Scanning ion conductance microscopy shows that these holes are actually pores through the interlamellar sheets. With the help of statistical analysis we can associate the pore-to-pore spacings in the interlamellar sheets with the observed offsets of successive nacre tablets. These results, supplemented by AFM, SEM, and TEM images, support and extend the model of biofabrication of gastropod nacre which is based on mineral bridges between the aragonite tablets.(in the aragonite polymorph) and proteins, exhibiting exceptional regularity and mechanical strength. 1,2,[18][19][20][21][22][23][24][25][26][27][28][29][30] The interdigitating brickwork array of crystals and

Cell surface macromolecules such as receptors and ion channels serve as the interface link between the cytoplasm and the extracellular region. Their density, distribution, and clustering are key spatial features influencing effective and proper physical and biochemical cellular responses to many regulatory signals. In this study, the effect of plasma-membrane receptor clustering on local cell mechanics was obtained from maps of interaction forces between antibody-conjugated atomic force microscope tips and a specific receptor, a vascular endothelial growth factor (VEGF) receptor. The technique allows simultaneous measurement of the real-time motion of specific macromolecules and their effect on local rheological properties like elasticity. The clustering was stimulated by online additions of VEGF, or antibody against VEGF receptors. VEGF receptors are found to concentrate toward the cell boundaries and cluster rapidly after the online additions commence. Elasticity of regions under the clusters is found to change remarkably, with order-of-magnitude stiffness reductions and fluidity increases. The local stiffness reductions are nearly proportional to receptor density and, being concentrated near the cell edges, provide a mechanism for cell growth and angiogenesis.

SummaryThe mechanisms behind natural nanofabrication of highly structured silicas are increasingly being investigated. We have explored the use of a standard Nanoscope III Multimode atomic force microscope (AFM) to study the silica shell of diatoms. The delicate structures of the shell surface of the diatom Navicula pelliculosa (Bre Âb.) Hilse were imaged and the shell's micromechanical properties were measured semi-quantitatively with a resolution down to approximately 10 nm. The technique to measure elasticity and hardness with the AFM was demonstrated to be useable even on these hard glass-like surfaces. Different experimental configurations and evaluation methods were tested. They gave a consistent result of the shell micromechanical properties. The first results showed that the diatom shell's overall hardness and elasticity was similar to that of known silicas. However, regions with different mechanical properties were distinguished. The elastic modulus varied from 7 to 20 GPa, from 20 to 100 GPa and from 30 to hundreds of GPa depending on the location. In general, the hardness measurements showed similar spatial differences. The hardness values ranged from 1 to 12 GPa but one specific part of the shell was even harder. Hence, certain localized regions of the shell were significantly harder or more elastic. These regions coincide with known characteristic features and mechanisms appearing at the different stages of the shell's growth. These results show that this method serves as a complementary tool in the study of silica biomineralization, and can detect eventual crystalline phases.

Morphology of aggregation intermediates, polymorphism of amyloid fibrils and aggregation kinetics of the “Arctic” mutant of the Alzheimer’s amyloid β-peptide, Aβ(1-40)(E22G), in a physiologically relevant TRIS buffer (pH 7.4) were thoroughly explored in comparison with the human wild type Alzheimer’s amyloid peptide, wt-Aβ(1-40), using both in situ atomic force and electron microscopy, circular dichroism and thioflavin T fluorescence assays. For arc-Aβ(1-40) at the end of the ‘lag’-period of fibrillization an abrupt appearance of ~3 nm size ‘spherical aggregates’ with a homogeneous morphology, was identified. Then, the aggregation proceeds with a rapid growth of amyloid fibrils with a variety of morphologies, while the spherical aggregates eventually disappeared during in situ measurements. Arc-Aβ(1-40) was also shown to form fibrils at much lower concentrations than wt-Aβ(1-40): ≤2.5 μM and 12.5 μM, respectively. Moreover, at the same concentration, 50 μM, the aggregation process proceeds more rapidly for arc-Aβ(1-40): The first amyloid fibrils were observed after ca 72 hours from the onset of incubation as compared to approximately 7 days for wt-Aβ(1-40). Amyloid fibrils of arc-Aβ(1-40) exhibit a large variety of polymorphs, at least five, both coiled and non-coiled distinct fibril structures were recognized by AFM, while at least four types of arc-Aβ(1-40) fibrils were identified by TEM and STEM and their mass-per-length statistics were collected suggesting supramolecular structures with two, four and six β-sheet laminae. Our results suggest a pathway of fibrillogenesis for full-length Alzheimer’s peptides with small and structurally ordered transient spherical aggregates as on-pathway immediate precursors of amyloid fibrils.

Self-powered photodetectors operating in the UV–visible–NIR window made of environmentally friendly, earth abundant, and cheap materials are appealing systems to exploit natural solar radiation without external power sources. In this study, we propose a new p–n junction nanostructure, based on a ZnO–Co3O4 core–shell nanowire (NW) system, with a suitable electronic band structure and improved light absorption, charge transport, and charge collection, to build an efficient UV–visible–NIR p–n heterojunction photodetector. Ultrathin Co3O4 films (in the range 1–15 nm) were sputter-deposited on hydrothermally grown ZnO NW arrays. The effect of a thin layer of the Al2O3 buffer layer between ZnO and Co3O4 was investigated, which may inhibit charge recombination, boosting device performance. The photoresponse of the ZnO–Al2O3–Co3O4 system at zero bias is 6 times higher compared to that of ZnO–Co3O4. The responsivity (R) and specific detectivity (D*) of the best device were 21.80 mA W–1 and 4.12 × 1012 Jones, respectively. These results suggest a novel p–n junction structure to develop all-oxide UV–vis photodetectors based on stable, nontoxic, low-cost materials.

In this work, we present all-oxide p-n junction core-shell nanowires (NWs) as fast and stable self-powered photodetectors. Hydrothermally grown n-type ZnO NWs were conformal covered by different thicknesses (up to 420 nm) of p-type copper oxide layers through metalorganic chemical vapor deposition (MOCVD).The ZnO NWs exhibit a single crystalline Wurtzite structure, preferentially grown along the [002] direction, and energy gap Eg=3.24 eV. Depending on the deposition temperature, the copper oxide shell exhibits either a crystalline cubic structure of pure Cu2O phase (MOCVD at 250 C) or a cubic structure of Cu2O with the presence of CuO phase impurities (MOCVD at 300 C), with energy gap of 2.48 eV.The electrical measurements indicate the formation of a p-n junction after the deposition of the copper oxide layer. The core-shell photodetectors present a photoresponsivity at 0V bias voltage up to 7.7 µA/W and time response ≤0.09 s, the fastest ever reported for oxide photodetectors in the visible range, and among the fastest including photodetectors with response limited to the UV region. The bare ZnO NWs have slow photoresponsivity, without recovery after the end of photo-stimulation. The fast time response for the core-shell structures is due to the presence of the p-n junctions, which enables fast exciton separation and charge extraction. Additionally, the suitable electronic structure of the ZnO-Cu2O heterojunction enables self-powering of the device at 0V bias voltage. These results represent a significant advancement in the development of low-cost, high efficiency and self-powered photodetectors, highlighting the need of fine tuning the morphology, composition and electronic properties of p-n junctions to maximize device performances.

No abstract

Combining a system for binding proteins to surfaces (Sigal, G. B., C. Bamdad, A. Barberis, J. Strominger, and G. M. Whitesides. 1996. Anal. Chem. 68:490-497) with a method for making ultraflat gold surfaces (Hegner, M., P. Wagner, and G. Semenza. 1993. Surface Sci. 291:39-46 1993) has enabled single, oriented, active Escherichia coli RNA polymerase (RNAP) molecules to be imaged under aqueous buffer using tapping-mode atomic force microscopy (AFM). Recombinant RNAP molecules containing histidine tags (hisRNAP) on the C-terminus were specifically immobilized on ultraflat gold via a mixed monolayer of two different omega-functionalized alkanethiols. One alkanethiol was terminated in an ethylene-glycol (EG) group, which resists protein adsorption, and the other was terminated in an N-nitrilotriacetic acid (NTA) group, which binds the histidine tag through two coordination sites with a nickel ion. AFM images showed that these two alkanethiols phase-segregate. Specific binding of the hisRNAP molecules was followed in situ by injecting proteins directly into the AFM fluid cell. The activity of the hisRNAP bound to the NTA groups was confirmed with a 42-base circular single-stranded DNA template (rolling circle), which the RNAP uses to produce huge RNA transcripts. These transcripts were imaged in air after the samples were rinsed and dried, since RNA also has low affinity for the EG-thiol and cannot be imaged under the buffers we used.